Under the guidance of : Co-ordinators : Group Leader : MRS. NEELAM (PRINCIPAL) GSKV A-Block, Vikas Puri, Delhi 1. Mrs. Archna TGT (Natural Science) GSKV, A-Block, Vikas Puri, Delhi 2. Mrs. Ritu Nangia TGT (Natural Science) GSKV, Hastsal, Delhi 4. Mrs. Roopa Arora TGT (Natural Science) GSKV, Hastsal, Delhi [Class-X – Science] 2 3 [Class-X – Science] Typology of Questions * One question of 3 marks will be included to assess the values inherent in the texts. 12×1=12 9×1=9 Practical Based Questions (PBQs) TOTAL 3×1=3 – Total (Theory Based Questions) 5. Evaluation and Multi-Disciplinary-(Appraise, judge, and/or justify the value or worth of a decision or outcome, or to predict outcomes based on values) – 4. High Order Thinking Skills (Analysis & Synthesis- Classify, compare, contrast, or differentiate between different pieces of information; Organize and/or integrate unique pieces of information from a variety of sources) – 3 – * Reasoning * Analytical Skills * Critical Thinking Skills etc. V. Short Ans. (VSA) (1 Mark) 3. Application (Use abstract information in concrete situation, to apply knowledge to new situations; Use given content to interpret a situation, provide an example, or solve a problem) 2. Understanding - (Comprehension to be familiar with meaning and to understand conceptually, interpret, compare, contrast, explain, paraphrase, or interpret information) 1. Remembering - (Knowledge based Simple recall questions, to know specific facts, terms, concepts, principles, or theories, identify, define, or recite, information) S.No. Time - 3 hrs. 6×2=12 3×2=6* 3×2=6 – 2 – 1 – Short Ans-I (SA) (2 Marks) 12×3=36 – 12×3=36 3 – 4 4 1 Short Ans-II (SA) (3 Marks) 6×5=30 – 6×5=30 2 1 1 1 1 Long Ans. (LA) (4 Marks) 90(36) 15(12) 75(24) 19 9 17 19 11 Total Marks 100% 25% 12% 23% 26% 15% % Weightage Marks : 90 CONTENTS Unit Chapter Page 1. Chemical Reactions and Equations 5 2. Acids, Bases and Salts 14 3. Metals and Non-Metals 27 4. Carbon and its Compounds 39 5. Periodic Classification of Elements 54 6. Life Processes 61 7. Control and Co-ordination 76 8. How do Organisms Reproduce 86 9. Heredity and Evolution 97 10. Light Reflection and Refraction 114 11. The Human Eye and the Colourful World 136 12. Electricity 149 13. Magnetic Effects of Electric Current 163 14. Sources of Energy 176 15. Our Environment 188 16. Management of Natural Resources 195 17. Solutions 201 18. Sample Papers 215 [Class-X – Science] 4 CHEMICAL REACTIONS AND EQUATIONS Chemical Reaction : Whenever a chemical change occurs we can say that a chemical reaction has taken place which can be expressed symbolically by a chemical equation. e.g. – – Food gets digested in our body Rusting of iron. e.g. magnesium is burnt in air to form magnesium oxide. This chemical reaction can be represented as 2Mg + O2 2MgO – We can observe or recognise a chemical reaction by observing change in state, colour, by evolution of gas or by change in temperature. – Physical state of the reactants and the products are mentioned to make chemical reaction more informative. e.g. we use (g) for gas, (l) for liquid, (s) for solid and (aq) for aqueous. Balancing Equation : We balance a chemical equation so that no. of atoms of each element involved in the reaction remains the same at the reactant and product side. e.g. Fe + H2O Fe2O3 + H2 can be written as 3 Fe(s) + 4H2O(g) Fe2O3(s) +4H2(g) Types of Reaction I. Combination Reaction :– The reaction in which two or more substances combine to form a new single substance. 5 [Class-X – Science] e.g. (i) CaO(s) + Calcium oxide Quick lime H2O(l) Ca(OH)2 Water Calcium hydroxide (slaked lime) (aq) – Ca(OH)2 slaked lime is used for white washing walls. It reacts with CO2 to form Calcium Carbonate and gives a shiny finish to the walls. Ca(OH)2 + CO2 (aq) (g) CaCO3 (s) Calcium Hydroxide + H2O (l) Calcium Carbonate (ii) Burning of Coal C(s) + O2(g) CO2(g) + heat + light (iii) Formation of water 2H2(g) + O2(g) 2H2O(l) Exothermic Reactions : Reaction in which heat is released along with the formation of products. e.g.. CH4(g) + 2O2(g) CO2(g) + 2H2O(g) – Respiration is also exothermic reaction. – De-composition of vegetable matter into compost. Endothermic Reaction : The reactions which require energy in form of heat, light or electricity are called endothermic reactions. e.g. – 2Ba(OH)2 + NH4Cl 2BaCl2 + NH4OH II. Decomposition Reactions : The reaction in which a single substance decomposes to give two or more substances. De composition reactions can be of three types: [Class-X – Science] 6 (i) (ii) (iii) – Silver bromide behaves similarly Sunlight 2Ag Br 2Ag(s) + Br2(g) – The above two reactions are used in black and white photography. 7 [Class-X – Science] III. Displacement Reaction : The chemical reaction in which an element displaces another element from its solution Fe(s) + CuSO4(aq) FeSO4 + Cu(s) Copper Sulphate (aq) Iron Sulphate Fe being more reactive than Cu displaces it from CuSO4 – The nail becomes brownish in colour and the blue colour of copper sulphate solution fades. – Other examples Zn(s) + CuSO4 ZnSO4 + Cu(s) (aq) (aq) Copper Sulphate Zinc Sulphate Pb(s) + CuCl2 PbCl2 (aq) (aq) Copper Chloride Lead Chloride + Cu(s) – Zinc and lead are more reactive elements than copper. They displace copper from its compounds. [Class-X – Science] 8 IV. Double Displacement Reaction : The reaction in which two different atoms or group of atoms are mutually exchanged e.g.. Na2 SO4 + BaCl2 BaSO4(s) + 2NaCl (aq) (aq) (aq) Sodium Barium Barium Sodium Sulphate Chloride Sulphate Chloride A white substance is formed due to above reaction. The insoluble substance i.e., BaSO4 is called precipitate. Precipitation Reaction – Any reaction that produces a precipitate is called a precipitation reaction. e.g.. Pb(NO3)2 (aq) + 2KI PbI2 +2KNO3 (aq) (aq) Lead Nitrate Potassium Lead Potassium Iodide Iodide Nitrate V Oxidation : Oxidation is the gain of oxygen or loss of hydrogen Heat 2CuO 2Cu + O2 e.g. When copper is heated a black colour appears. If this CuO is reacted with hydrogen gas then again Cu becomes brown as reverse reaction takes place Heat Cu + H2O CuO + H2 VI Reduction : Reduction is the loss of oxygen or gain of hydrogen. – Redox Reaction : The reaction in which one reactant gets oxidised while other gets reduced 9 [Class-X – Science] ZnO + C Zn + CO e.g. MnO2 + 4HCl MnCl2 + 2H2O + Cl2 – Corrosion : When a metal is attacked by substances around it such as moisture, acids etc. (i) Rusting of iron. i.e Reddish brown coating on iron of Fe2O3 is formed. (ii) Black coating on Silver. Rusting of iron can be prevented by painting, oiling the surface or by galvanisation. – Rancidity : When fats and oils are oxidised they become rancid and their smell and taste change. – Antioxidants are added to foods containing fats and oil. e.g. N2 is added to packet of chips to prevent oxidation of fats and oils. Answer the following questions very briefly (1 Mark) 1. What happens when the milk is left at room temperature during summer? 2. Write a balanced chemical equation for the reaction that takes place when magnesium is burnt in air to give magnesium oxide. 3. A substance under goes chemical reactions to produce two or more simpler products, what type of reaction is this? 4. Why do copper vessels lose their shine when exposed to air? 5. Fe2O3 + 2Al Al2O3 + 2Fe The above reaction is an example of which type of reaction. [Class-X – Science] 10 6. Name the type of reaction in which energy is absorbed. 7. Why does the colour of copper sulphate solution change when an iron nail is dipped into it? 8. Give an example of decomposition reaction which proceeds by absorbing electric energy. 9. Why do we balance a chemical equation? 10. Why is respiration called as an exothermic reaction? 11. Why is digestion called as decomposition reaction? 12. Why are the bags of potato chips usually flushed with nitrogen gas? Answer the following questions briefly (2 marks) 1. Write down the observations which indicate the occurrence of a chemical reaction. 2. Write the balanced chemical equation for the given word equations– (a) Hydrogen gas combines with nitrogen to form ammonia. (b) Potassium metal reacts with water to give potassium hydroxide and hydrogen gas. 3. Identify the substances that are oxidised and the substances that are reduced in the following reactions. (i) Na + (s) (ii) CuO (s) O2 Na2O (g) + H2 (s) Cu + H2 O(l) (g) (s) 4. What happens when silver chloride is exposed to sunlight? Give one practical application of this reaction. Write the balanced chemical equation also. 5. Write any two changes observed by you when ferrous sulphate is heated. Write the balanced chemical equation of the reaction. 6. BaCl2 + Na2SO4 2NaCl + BaSO4 11 [Class-X – Science] (i) Identify the type of chemical reaction represented by the above chemical equation. (ii) Give another example of this type of chemical reaction with equation. 7. Compound ‘X’ decomposes to form compound ‘Y’ and CO 2 gas. Compound ‘Y’ is used in the manufacturing of cement. (i) Name the compounds X and Y. (ii) Write the chemical equation for this decomposition reaction. 8. What is rancidity? Write two ways by which it can be prevented? Answer the following questions in detail (3 marks) 1. Write down the balanced chemical equations for the following reactions. (a) Zinc carbonate(s) Zinc oxide + Carbon dioxide(g) (b) Aluminium(s) + Chlorine(g) Aluminium chloride(s) (c) Magnesium(s)+ Water(l) hydrogen(g) Heat Magnesium hydroxide(l)+ 2. Classify the given chemical reactions into combination, displacement and double displacement reactions. (i) MnO2(s) + 4HCl(l) MnCl2(s) + Cl2(g) + 2H2O(l) (ii) CaO(s) + CO2(g) CaCO3(s) (iii) 2AgCl(s) 2Ag(s) + Cl2(g) 3. What happens when CO2(g) is passed through slaked lime? Write the balanced chemical equation. Write the type of reaction that has occurred. 4. Define corrosion. Give two examples. Why is corrosion of iron a serious problem. How can it be prevented? [Class-X – Science] 12 Explain the following questions detail (5 marks) 1. Balance the following chemical equations and identify the type of reaction they represent KClO3 KCl + O2 NH3 + O2 NO2 + H2O Na2O + H2O NaOH Na + H2O NaOH + H2 FeCl3 + NaOH Fe (OH)3 + NaCl. 2. Define various types of chemical reactions. Write one example of each type with chemical equations. 13 [Class-X – Science] CHAPTER – 2 ACIDS, BASES AND SALTS Acids – Sour in taste Bases – Bitter in taste – Changes blue litmus into red – Changes red litmus into blue – e.g. Hydrochloric acid HCl – e.g. Sodium hydroxide NaOH – Sulphuric acid H2SO4 – Potassium hydroxide KOH – Nitric acid HNO3 – Calcium hydroxide Ca(OH)2 – Acetic acid CH3 COOH – Ammonium hydroxide NH4OH Some naturally occurring acids Vinegar – Acetic Acid Orange – Citric Acid Lemon – Citric Acid Tamarind – Tartaric Acid Tomato – Oxalic Acid Sour milk (Curd) – Lactic Acid Ant and Nettle sting – Methanoic Acid Acid – Base Indicators – Indicate the presence of an acid or base in a solution. Litmus solution – It is a natural indicator. It is a purple dye extracted from Lichens. Other examples are Red Cabbage and coloured petals of Petunia and turmeric. [Class-X – Science] 14 Olfactory indicators : Show odour changes in acidic or basic media. e.g. onion and clove. Acid – Base Indicators S.No. Name of the Indicator Colour Change Colour Change with Acid with Base A. Blue litmus solution To red No change B. Red litmus solution No change To blue C. Turmeric No change To red D. Methyl orange To red To yellow E. Phenolphthalein (colourless) No change To pink Dilute Acid : Contains only a small amounts of acid and a large amount of water. Concentrated Acid : A concentrated acid contains a large amount of acid and a small amount of water. Chemical Properties of Acids and Bases (i) Reaction with metal Acid + Metal Salt + Hydrogen (Refer activity 2.3 on page No. 19 of NCERT Book) 2HCl + Zn ZnCl2 + H2 2HNO3 + Zn Zn (NO3)2 + H2 H2SO4 + Zn ZnSO4 + H2 2CH3COOH + Zn (CH3COO)2 Zn + H2 Pop test : When a burning candle is brought near a test tube containing hydrogen gas it burns with a ‘Pop’ sound. This test is conducted for examining the presence of hydrogen gas. 15 [Class-X – Science] Base + Metal Salt + Hydrogen NaOH + Zn Na2ZnO2 + H2 Sodium Zincate Note – Such reactions are not possible with all the metals. Action of Acids with metal Carbonates and metal bicarbonates Metal Carbonate + Acid Salt + Carbondioxide + Water Na2CO3(s) + 2HCl(aq) 2NaCl(aq) + CO2(g) + H2O(l) Metal bicarbonate + Acid Salt + Carbondioxide + Water NaHCO3 + HCl NaCl + CO2 + H2O Lime water Test : On passing the evolved CO2 gas through lime water, we find that lime water turns milky. Ca(OH)2 (aq) + CO2(g) CaCO3(s) + H2O(l) Lime water White precipitate On passing excess CO2 the following reaction takes place CaCO3(s) + H2O(l) + CO2(g) Ca(HCO3)2 aq Soluble in water Reaction of acids and bases with each other to give salt and water are called Neutralisation Reactions Base + Acid Salt + Water NaOH(aq) + HCl(aq) NaCl(aq) + H2O(l) e.g. Reactions of metal oxides with acids Metal Oxide + Acid Salt + Water CuO + Copperoxide [Class-X – Science] HCl CuCl2 + Hydrochloric Copper + Water acid chloride 16 H2O Note : Appearance of blue green colour of the solution because of formation of CuCl2. Metallic oxides are said to be basic in nature because they give salt and water on reacting with acids. Reaction of Non Metallic Oxide with Base Non-metallic oxide + Base Salt + Water CO2 + Ca(OH)2 CaCO3 + H2O Note : Non Metallic oxides are said to be acidic in nature because on reacting with a base they produce salt and water. All acidic solutions conduct electricity because of formation of (H+) ions in aq. solution. Refer activity 2.3 on page 22 of NCERT Book – Glowing of bulb indicates that there is a flow of electric current through the solution. Acids or bases in a Water Solution Acids produce H+ions in the presence of water HCl + H2O H3O+ + Cl– H3O+ – Hydronium ion. – H+ ion cannot exist alone. It exists as H+(aq) or (H3O+) hydronium ion. i.e., H+ + H2O H3O+ – Bases provide (OH–) ions in the presence of water HO 2 NaOH(s) Na+(aq) + OH–(aq) HO 2 KOH(s) K+(aq) + OH–(aq) 17 [Class-X – Science] HO 2 Mg(OH)2(s) Mg2+(aq) + 2OH–(aq) Alkalis All bases donot dissolve in water. An alkali is a base that dissolves in water. Common alkalis are NaOH Sodium hydroxide KOH Potassium hydroxide Ca(OH)2 Calcium hydroxide NH4OH Ammonium hydroxide Note : All alkalis are bases but all bases are not alkalis. Precaution must be taken while mixing acid or base with water. The acid must always be added to water with constant stirring as it is a highly exothermic reaction. When an acid or a base is mixed with water they become dilute. This results in the decrease in the concentration of H3O+ or OH– per unit volume in acids and bases respectively. Strength of an Acid or Base Strength of acids and bases depends on the no. of H+ions and OH–ions produced respectively. With the help of a universal indicator we can find the strength of an acid or base as it shows different colours at different concentrations of hydrogen ions in a solution. A scale for measuring hydrogen ion conc. in a solution called pH scale has been developed. pH = Potenz in German means power. This scale measures from 0 (very acidic) to 14 (very alkaline) 7 indicates Neutral pH (water is neutral). [Class-X – Science] 18 pH paper : Is a paper which is used for measuring pH. Variation of PH S. PH No. Value Colour of the pH Paper Nature of Solution H+ion Conc. Highly acidic very high OH– ion Conc. 1. 0 Dark red 2. 4 Orange or yellow Acidic high low 3. 7: Green Neutral Equal Equal 4. 10 Bluish green or blue Alkaline low high 5. 14 Dark blue or violet Weak Acids e.g. CH3 COOH H2CO3 highly basic very low + H ion conc. Weak Base e.g. NH4OH – OH ion conc. very low very high Strong Acids e.g. HCl H2SO4 HNO3 Strong Acids e.g. KOH NaOH Ca(OH)2 Importance of pH in our daily life Importance of pH in our digestive system – Our stomach produces hydrochloric acid. This dilute hydrochloric acid help in digestion of food. In case of indigestion our stomach produces acid in a very large quantity because of which we feel pain and irritation in our stomach. To get relief from this pain antacids are used. These antacids neutralise the excess acid and we get relief. pH of Acid Rain : When pH of rain water is less than 5.6 it is called acid rain. Flow of acidic rain in water bodies makes them acidic causing a threat to the survival of aquatic life. pH of Soil : Plants require a specific range of pH for their healthy growth. If pH of soil of any particular place is less or more than normal 19 [Class-X – Science] then the farmers add suitable chemicals to it. Our body functions between the pH range of 7.0 to 7.8. Living organisms can survive only in the narrow range of pH change. Tooth decay and pH : Bacteria present in the mouth produces acids by degradation of sugar and food particles remaining in the mouth. Tooth decay begins below the pH 5.6. Using toothpaste which is generally basic, can neutralise the excess acid and prevent tooth decay. Bee sting or Nettle sting contains methanoic acid which causes pain and irritation. Using a weak base like baking soda neutralises the acid giving relief. Salts and their Derivation S. No. Name of Salt Formula Derived from Derived from 1. Potassium Sulphate K2SO4 KOH H2SO4 2. Sodium Sulphate Na2SO4 NaOH H2SO4 3. Sodium Chloride NaCl NaOH HCl 4. Ammonium Chloride NH4Cl NH4OH HCl Note : NaCl and Na2 SO4 belong to the family of sodium salts as they have the same radicals. Similarly NaCl and KCl belong to the family of chloride salts. Neutral Salts : Strong Acid + Strong base pH value is 7 e.g. NaCl, CaSO4 Acidic Salts : Strong Acid + weak base pH value is less than 7 eq. NH4Cl, NH4 NO3 Basic Salts : Strong base + weak acid pH value is more than 7 e.g. CaCO3, CH3 COONa [Class-X – Science] 20 NaCl – Sodium chloride is called as common salt. It is derived from seawater. – Rock Salt is mined like coal, is brown coloured and crystalline is shape. Uses 1. Common salt is an important raw material for many materials of daily use such as. Sodium hydroxide Washing Soda Bleaching Power. 2. Used in our food. Sodium Hydroxide : NaOH, Common Name – caustic soda. Preparation : Prepared by the method called chlor-alkali process. It is called so because we get chlorine and an alkali (NaOH) in this process. 2NaCl(aq) + 2H2O(l) 2NaOH(aq) + Cl2(g) + H2(g) 21 [Class-X – Science] Calcium oxy chloride – CaOCl2 Common Name : Bleaching Powder Preparation Ca(OH)2 + calcium hydroxide Cl2 CaOCl2 chlorine bleaching power + H2O water Uses (1) Used in textile industry and laundry. (2) Used as disinfectant of water III. Sodium Hydrogen Carbonate – NaHCO3 – Common name – Baking Soda Preparation NaCl + H2O + CO2 + NH3 NH4Cl + NaHCO3 Sodium Water chloride 1. Carbon Ammonia Sodium hydrogen carbonate dioxide Used in backing/cooking Heating NaHCO3 produces CO2 NaHCO3 Heat Na2CO3 + H2O + CO2 CO2 produced causes dough to rise and helps to make cakes and pastries spongy. Used as ingredients of antacid Sodium Carbonate – Na2CO3 Common name : Washing Soda Preparation : Recrystallisation of sodium carbonate Na2CO3 + 10H2O [Class-X – Science] Heat Na2CO3. 10H2O 22 Uses – Used in glass, soap and paper industry – Cleaning agent for domestic purposes. – Removal of hardness of water. – Manufacturer of borax. V. Calcium Sulphate hemihydrate CaSO4. 1 HO 2 2 Common Name : Plaster of Paris Water of crystallisation : Fixed no. of water molecules present in one formula unit of a salt. – On heating copper sulphate crystals water droplets appear, formula of hydrated copper sulphate – CuSO4. 5H2O. – gypsum also contains water of crystallisation. CaSO4.2H2O – Preparation : On heating gypsum at 373K it becomes 1 CaSO4. H2O i.e. plaster of paris. 2 373 K CaSO 4 .2H 2O CaSO 4 – 1 H 2O 2 When Plaster of Paris is mixed with water it changes to gypsum. CaSO4.½ H2O + 1½ H2O CaSO4.2H2O POP GYPSUM Uses of plaster of Paris : Making toys, decorative material and smoothening surfaces, plaster for fractured bones. 23 [Class-X – Science] Very Short Answer Type Questions (1 mark) 1. Two solutions A and B have pH 4 and 9 respectively. Which solution has more H+ ion concentration? 2. Why should curd and sour substances not be kept in brass and copper vessel? 3. What is the chemical name of bleaching powder? 4. Write down the molecular formula of one strong and one weak acid. 5. Explain why Plaster of Paris should be stored in a moisture proof container? 6. Name the gas evolved when dil. sulphuric acid acts on sodium carbonate. How will you test for the presence of the gas? 7. What is the use of common salt in soap industry? 8. What do you observe when a burning candle is brought near the testtube containing zinc and hydrochloric gas? 9. Name the indicator used to measure pH values over the whole range. 10. Write the formula of washing soda and baking soda. Short Answer Type Questions (2 marks) 1. Write two physical properties of an acid CO 2 ? Name the products 2. Complete the reaction CaCO3 + H2O formed. 3. A test tube contains solution of NaOH and Phenolphthalein. What is the colour of the solution? On adding HCl, what colour change is observed and why? 4. Why are metallic oxides called as basic oxides and non-metallic oxides called acidic oxides? 5. In a beaker a solution of HCl is poured and an electric circuit with a bulb is placed systematically. What happens to the bulb and why? [Class-X – Science] 24 What will happen if HCl is replaced by NaOH? 6, Identify the type of reaction H X + M OH MX + HOH Explain this reaction with an example. 7. Why are all bases not alkalies but all alkalis are bases? 8. What is pH value. What is the pH value of a salt formed by a (i) weak acid and strong base (ii) strong acid and strong base. 9. Name the process used for the production of sodium hydroxide. Write the chemical equation for this process. 10. Why is sodium hydrogen carbonate used as an ingredient in antacid. Give one more use of this compound. Answer the following Questions in detail (3 marks) 1. What is acid rain? What colour does it give with the pH paper? How does it affect the aquatic life? 2. (i) What happens when a metal reacts with dilute hydrochloric acid? Write the balanced chemical equation also. (ii) Complete the following equation. © NaOH + Zn _________ + _________. 3. What happens when an acid or a base is added to water? Why does the beaker appear warm? Why should we always add acid or base to water and not water to the acid or base. 4. Give reasons (i) Use of a mild base like baking soda provides relief on the area stung by honey bee. 25 [Class-X – Science] (ii) Baking powder is added to make the cakes spongy and soft. (iii) The colour of blue copper sulphate crystals changes to white on heating. Answer the following Questions in detail 1. (5 marks) (a) Write down five products formed with the help of common salt on industrial level. (b) Write down the chemical name of these compounds and one use of each of them. 2. Fill in the blanks a) Acid + ______ Salt + Water.. b) _____ + Metal Salt + _____ c) Metal carbonate / metal hydrogen carbonate + acid _______ + _______ + _______. H2 O d) NaOH _______ + _______ e) Na2CO3 + 10H2O _______. 3. (i) A compound ‘X’ is added to make pakoras crispy and also for faster cooking. Write the chemical name and formula of the compound ‘X’. Also write the balanced chemical equation of the reaction of production of compound ‘X’. List two other uses of compound ‘X’. (ii) Write the chemical equation of the reaction used in the preparation of bleaching powder and washing soda. [Class-X – Science] 26 CHAPTER – 3 METALS AND NON-METALS About 118 elements are known today. There are more than 90 metals, 22 non metals and a few metalloids. Sodium (Na), potassium (K), magnesium(Mg), aluminium(Al), calcium(Ca), Iron(Fe), Barium(Ba) are some metals. Oxygen(O), hydrogen(H), nitrogen(N), sulphur(S), phosphorus(P), fluorine(F), chlorine(Cl), bromine(Br), iodine(l) are some non-metals. Physical Properties of Metals and Non-Metals Metals Non-metals 1. Generally solid except Hg. 1. Can be solid, liquid orgas e.g., C is solid, Br (liq), H2 (gas) 2. Ductile, Malleable (drawn into wires) (beaten into sheets) 2. Non-ductile, non-Malleable 3. Sonorous (produces sound) 3. Non-sonorous 4. Lustrous (have natural shine) 4. Non-lustrous except Iodine. 5. High Melting Point except Ce and Ga 5. Lower M.P. than metals. 6. Generally good conductors of heat and electricity except Pb and Hg. 6. Bad conductors of heat and electricity except Graphite (form of C) 7. High density except Na and K 7. Low densities except Diamond (form of C) Metals form basic oxides e.g., Magnesium oxide(MgO), while nonmetals form acidic oxides e.g., SO2, CO2. Ag and Cu are best conductors 27 [Class-X – Science] Chemical Properties of Metals 1. Reaction with air : Different metals show different reactivities towards oxygen present in air. Metals can burn in air, react or don’t react with air. Metal + oxygen Metal Oxide Some metals like Na and K are kept immersed in kerosene oil as they react vigorously with air and catch fire. Some metals like Mg, Al, Zn, Pb react slowly with air and form a protective layer. Mg can also burn in air with a white dazzling light to form its oxide Fe and Cu don’t burn in air but combine with oxygen to form oxide. Iron filings burn when sprinkled over flame. Metals like silver, platinum and gold don't burn or react with air. e.g. 2Na + O2 Na2O 2Mg + O2 2MgO 2Cu + O2 2CuO 4Al + 302 2Al2O3 Amphoteric Oxides : metal oxides which react with both acids as well as bases to form salt and water e.g. Al2O3, ZnO. e.g. Al2O3 + HCl AlCl3 + H2O Al2O3 + NaOH NaAlO2 + H2O 2. REACTION WITH WATER : React with hot water e.g. Mg React with cold water e.g. Na, K, Ca Metals [Class-X – Science] 28 React with steam only e.g. Fe and Al, Zn to form their oxides and H2 Na + H2O NaOH + H2 K + H2O KOH + H2 Ca + H2O Ca(OH)2 + H2 Mg + H2O Mg(OH)2 + H2 In case of Ca and Mg, the metal starts floating due to bubbles of hydrogen gas sticking to its surface. Al + H2O Al2O3 + H2 Fe + H2O Fe3O4 + H2 Note : Try Balancing the above Chemical equations yourself 3. Reaction with dilute acids: Metal + dilute acid Salt + Hydrogen gas Metals react with dilute hydrochloric acid and dilute sulphuric acid to form salt and hydrogen gas. + 2HCl FeCl2 + H2 Mg + 2HCl MgCl2 + H2 Zn + 2HCl ZnCl2 + H2 2Al + 6HCl 2AlCl3 + 3H2 Fe Note : Copper, mercury and silver don’t react with dilute acids. Hydrogen gas produced is oxidised to water. This happens because HNO3 is a strong oxidising agent when metals react with nitric acid (HNO3). But Mg and Mn, react with very dilute nitric acid to evolve hydrogen gas. Mg + 2HNO3 Mg(NO3)2 + H2 4. Reaction of metals with other metal salts : Metal A + Salt solution Salt solution of B + Metal B of A 29 [Class-X – Science] All metals are not equally reactive. Reactive metals can displace less reactive metals from their compounds in solution. This forms the basis of reactivity series of metals. Reactivity series is a list of metals arranged in order of their decreasing activities. e.g. Fe + CuSO4 FeSO4 + Cu Zn + CuSO4 ZnSO4 + Cu Reaction between Metals and Non-Metals – Reactivity of elements can be understood as a tendency to attain a completely filled valence shell. – Atom of metals can lose electrons from valence shells to form cations (+ve ions). – Atom of non-metals gain electrons in valence shell to form anions (– ve ions). – Oppositely charged ions attract each other and are held by strong electrostatic forces of attraction forming ionic compounds. Formation of MgCl2 Mg 2,8,2 [Class-X – Science] Mg2+ + 2,8 (Magnesium ion) 30 2e– Cl2 2,8,7 + 2e– 2Cl– 2,8,8 (Chloride ion) Properties of Ionic Compounds – Are solid and mostly brittle. – Have high melting and boiling points. More energy is required to break the strong inter-ionic attraction. – Generally soluble in water and insoluble in kerosene, petrol. – Conduct electricity in solution and in molten state. In both cases, free ions are formed and conduct electricity. Occurrence of Metals Minerals : Elements or compounds occurring naturally are minerals. ORES : Mineral from which metal can be profitably extracted is an ore. For example, sulphide ore, oxide ore, carbonate ore. – Metals at the bottom of activity series like gold, platinum, silver, copper generally occur in free state. But copper and silver also occur as sulphide and oxide ores. – Metals of medium reactivity (Zn, Fe, Pb etc.) occur mainly as oxides, sulphides or carbonates. – Metals of high reactivity (K, Na, Ca, Mg and Al) are very reactive and are thus found in combined state. 31 [Class-X – Science] GANGUE : Ores are naturally found mixed with impurities like soil, sand, etc. called gangue. The gangue is removed from the ore. METALLURGY : Step-wise process of obtaining metal from its ore. I. *Enrichment of ore II. *Obtaining metal from enriched ore. III. *Refining of impure metal to obtain pure metal. I. II. Enrichment of Ores : It is the process of the removal of impurities such as soil, sand etc. from the ore prior to extraction of the metal. Different separation techniques are used based on physical or chemical properties of ore. Extracting Metals from the Enriched Ore Extracting Metals Low in the Activity Series : By heating the ores in air at high temperature. e.g. *Mercury from cinnabar 2H gS + 3O 2 Heat 2HgO + 2SO2 Heat 2Hg + O2 2HgO e.g *Copper from copper sulphide Heat 2Cu2O _ 2SO2 Cu2S + 3O2 Heat 6Cu + SO2 2Cu2O + Cu2S Extracting Metals in the Middle of Activity Series : *Metals are easier to obtain from oxide ores, thus, sulphide and carbonate ores are converted into oxides. *Metal ore heated strongly in excess of air (Roasting) [Class-X – Science] 32 Heat 2ZnO + 2SO2 e.g 2ZnS + 3O2 Metal ore heated strongly in limited or no supply of air (Calcination) Heat ZnO + CO2 e.g ZnCO3 Reduction of Metal Oxide : 1. USING COKE : Coke as a reducing agent. Heat Zn + CO ZnO + C 2. USING DISPLACEMENT REACTION : highly reactive metal like Na, Ca and Al are used to displace metals of lower reactivity from their compounds. These displacement reactions are highly exothermic. Heat 3Mn + 2Al2O3 + heat MnO2 + 4Al Heat 2Fe + Al2O3 + heat Fe2O3 + 2Al Thermite Reaction : Reduction of a metal oxide to form metal by using Al powder as a reducing agent. This process is used to join broken pieces of heavy iron objects or welding. Extracting Metals at the Top of Activity Series – These metals have more affinity for oxygen than carbon so they cannot be obtained from their compounds by reducing with carbon. – So are obtained by electrolytic reduction. e.g. Sodium is obtained by electrolysis of its molten chloride NaCl Na+ + Cl– As electricity is passed through the solution metal gets deposited at cathode and non-metal at anode. – At cathode : e.g. Na+ + e– Na – At anode : 2Cl– Cl2 + 2e– 33 [Class-X – Science] III. Refining of Metals – Impurities present in the obtained metal can be removed by electrolytic refining. Copper is obtained using this method. Following are present inside the electrolytic tank. – Anode – slab of impure copper – Cathode – slab of pure copper – Solution – aqueous solution of copper sulphate with some dilute sulphuric acid – From anode copper ions are released in the solution and equivalent amount of copper from solution is deposited at cathode. – Insoluble impurities containing silver and gold gets deposited at the bottom of anode as anode mud. Corrosion – Metals are attacked by substances in surroundings like moisture and acids. – Silver - it reacts with sulphur in air to our form silver sulphide and articles become black. – Copper - reacts with moist carbon dioxide in air and gains a green coat of copper carbonate. [Class-X – Science] 34 – Iron-acquires a coating of a brown flaky substance called rust. Both air and moisture are necessary for rusting of iron. Rust is hydrated Iron (III) oxide i.e. Fe2O3.xH2O Prevention of Corrosion – Rusting of iron is prevented by painting, oiling, greasing, galvanizing, chrome plating, anodising and making alloys. – In galvanization, iron or steel is coated with a layer of zinc because oxide thus formed is impervious to air and moisture thus protects further layers from corrosion. Alloys : These are homogeneous mixture of metals with metals or nonmetals. – Adding small amount of carbon makes iron hard and strong. Name of Alloy Properties Constituent metal / Non-metal 1. Steel Hard Iron and carbon 2. Stainless steel Hard Rust Free Iron, nickel and chromium 3. Brass Low electrical conductivity Copper and zinc 4. Bronze than pure metal Copper and tin 5. Solder Low MP, used to weld wires Lead and tin 6. Amalgam Used by dentists Mercury and any other metal (1 Mark) 1 Name a metal which is the best conductor of electricity and one which is poor conductor of electricity. 2 Why food cans are coated with tin and not with zinc? 3. Name any two alloys whose electrical conductivity is less than that of pure metals. 35 [Class-X – Science] 4. Name the non-metal with lustre. 5. What are amphoteric oxide. Give one example. 6. An aqueous solution of Al 2O3 is electrolysed. Name the element collected at anode. 7. An oxide of an element was dissolved in water. The final solution turned red litmus blue. What is the nature of oxide. Is the element metal, non-metal or a metalloid? 8. What happens when cinnabar is heated? Write the balanced chemical equation. 9. Ionic compounds have high melting point. Why? 10. Name two metals which are found in nature in free state. 1. Why do magnesium and calcium float when they react with water? 2. Write the chemical equations of heating of Cu and Fe. 3. Write two chemical equations to show that Al2O3 is an amphoteric oxide. 4. What is galvanization? Why it is done? 5. Why is hydrogen gas generally not evolved when metals react with nitric acid. Name two metals which react with HNO3 to evolve H2 gas. 6. Explain the thermite process. Write the chemical equation involved. 7. Distinguish between roasting and calcination. 8. Every ore is a mineral but not every mineral is an ore. Explain. 9. Why can highly reactive metals not be obtained from their oxides using coke as a reducing agent? [Class-X – Science] 36 10. What is an amalgam? Write the constituent metals of brass? 1. Ionic compounds are good conductors of electricity under specific conditions. Name the two conditions and give reasons. 2. Why are metal sulphides and carbonates converted to oxides prior to reduction. Write the equation for the chemical reactions that take place during (i) roasting; (ii) calcination of zinc ores. 3. What is an alloy? How is it prepared? Name the alloy which is used for welding electrical wires together. 1. (i) What is reactivity series of metals? Arrange the metals zinc, magnesium, aluminium, copper and iron in a decreasing order of reactivity. (ii) What will you observe when you put (a) Some zinc pieces into blue copper sulphate solution. (b) Some copper pieces into green ferrous sulphate solution. (iii) write the balanced chemical equations too. 2. Give reasons: (i) Platinum, gold and silver are used to make jewellery. (ii) Sodium and potassium are stored under oil. (iii) Aluminium is a highly reactive metal, still it is used to make utensils for cooking. (iv) Carbonate and sulphide ores are usually converted into oxides during the process of extraction. 37 [Class-X – Science] (v) Highly reactive metals are obtained from their ores by the process of electrolysis and not reduction with carbon. METALS AND NON-METALS : IN BRIEF – Metals are generally solid, sonorous, lustrous, good conductor of heat and electricity, malleable, ductile, high melting point, high densities, form basic oxides, form +vely charged ion. – Non-metals are generally solid or gas, non-lustrous, non-sonorous, bad conductor of heat and electricity, have low melting point, form acidic oxides and form -vely charged ions. – Metals like Na, K and Ca are highly reactive, while others like Magnesium, Aluminium, Zinc and Lead are less reactive and some others are least reactive like silver, gold and platinum. – Metals generally displace hydrogen from acids. – Reactivity series is based on displacement capability of metals and is a series of metals in the order of their decreasing reactivity. – Metals and non-metals react to form ionic compounds which are soluble in water, have high melting point and are good conductor of electricity in their aqueous solution or molten state. – Ores are minerals from which a metal can be profitably extracted. – Metals are extracted from their ores according to their reactivity. – Sulphide and chloride ores are roasted while carbonate ores are calcinated. – Pure metals can be obtained using electrolytic refining process. – Metals are generally attacked by air and corrode. To alter the properties of metals alloys are made. – Steel, stainless steel, amalgams, brass, bronze and solder are some alloys. [Class-X – Science] 38 CHAPTER – 4 CARBON AND ITS COMPOUNDS Carbon is a versatile element. Found in .02% in form of minerals and 03% in form of CO2. All living structures are carbon based. Covalent Bond in Carbon – The atomic number of carbon is 6 and its electronic configuration is 2, 4. To attain a noble gas configuration. – It is difficult for an atom of carbon to either gain or lose electrons as it would be difficult to hold extra electrons and would require a large amount of energy to remove four electrons. – Carbon attains the noble gas configuration by sharing its valence electrons with other atoms. Atoms of other elements like hydrogen, oxygen, nitrogen, chlorine also show sharing of valence electrons. e.g. (a) (b) 39 [Class-X – Science] (c) – It is evident that the number of shared pair of electrons can be one, two or three. Try making the structures of H2O and CH4. – Bond formed by the sharing of an electron pair between two atoms is called covalent bond. – Covalently bonded molecules have low melting and boiling points because of comparatively weaker intermolecular forces, unlike ionic compounds. – These molecules are generally poor conductor of electricity since no charged particles are formed. Versatile Nature of Carbon Atoms Two important properties which enable carbon to form enormously large number of compounds. I. CATENATION is property of carbon atom to form bond with other atoms of carbon. Like carbon, silicon forms compounds with hydrogen upto seven or eight atoms of silicon. [Class-X – Science] 40 II. TETRAVALENCY : Having a valency of 4, carbon atom is capable of bonding with atoms of oxygen, hydrogen, nitrogen, sulphur, chlorine and other elements. The smaller size of carbon atom enables nucles nucleus to hold the shared pair of electrons strongly, thus carbon compounds are very stable in general. Saturated and Unsaturated Carbon Compounds – ALKANE : CnH2n+2 – ALKENE : CnH2n – ALKYNE : CnH2n–2 – Electron dot structure of a saturated carbon compound, ethane is as follows: – Electron dot structure of an unsaturated carbon compound, ethene is as follows: 41 [Class-X – Science] TRY DRAWING THE ELECTRON DOT STRUCTURE OF ETHYNE Formulae and Structures of Saturated Compounds of Carbon and Hydrogen [Class-X – Science] 42 On the basis of structures the hydrocarbons can be: Structural isomers : these are the compounds having identical molecular formula but different structures. For example, isomers of butane. Heteroatom and Functional Group * In hydrocarbon chain, one or more hydrogen atoms can be replaced by other atoms in accordance with their valencies. The element that replaces hydrogen is called a heteroatom. * These heteroatoms and the group containing them impart chemical properties to the compound and hence are called functional groups. 43 [Class-X – Science] Homologous Series – It is a series of compounds in which the same functional group substitutes for hydrogen in a carbon chain. – For instance, the ALCOHOLS: CH3 OH, C2H5 OH, C3H7 OH, C4H9 OH. – The successive member differs by –CH2-; unit and 14 units of mass. – The chemical properties are imparted by the functional group thus all members have similar chemical properties. But the members have different physical properties. – The physical properties vary among the members of homologous series due to difference in their molecular mass. – Melting point and boiling point increases with increasing molecular mass. Nomenclature of Carbon Compounds 1. Identify the number of carbon atoms in the compound. 2. Functional group is indicated either by prefix or suffix. [Class-X – Science] 44 Functional Group Suffix Alkene ene Alkyne yne Alcohol ol Aldehyde al Ketone Prefix one Carboxylic acid oic acid chlorine chloro 3. If a suffix is added, then final ‘e’ is removed from the name e.g. methanol (methane-e = methan + ol). Chemical Properties of Carbon Compounds 1. COMBUSTION *Carbon compounds generally burn (oxidize) in air to produce carbon dioxide and water, and release heat and light energy. CH4 + O2 CO2 + H2O + heat and light *Saturated hydrocarbon burns generally with a blue flame in good supply or air and with a yellow sooty flame in limited supply of air. *Sooty flame is seen when unsaturated hydrocarbons are burnt. *Burning of coal and petroleum emits oxides of sulphur and nitrogen which are responsible for acid rain. 2. OXIDATION : *Alcohols can be converted to carboxylic acids by oxidizing them using alkaline potassium permanganate or acidified potassium dichromate (they add oxygen to the reactant, thus are called oxidizing agents). 45 [Class-X – Science] Alkaline KMnO4 + heat CH 3 – CH 2 OH CH 3COOH Acidified K 2 Cr2 O7 +heat 3. ADDITION REACTION Hydrogen is added to unsaturated hydrocarbon in presence of palladium or nickel as catalyst. Vegetable oils are converted into vegetable ghee using this process. Saturated fatty acids are harmful for health and oils with unsaturated fatty acids should be used for cooking. 4. SUBSTITUTION REACTION In saturated hydrocarbons, the hydrogen attached to carbon can be replaced by another atom or group of atoms in presence of sunlight. CH4 + Cl2 CH3Cl + HCl (sunlight required) IMPORTANT CARBON COMPOUNDS : Ethanol and Ethanoic Acid Ethanol *Consumption of dilute ethanol causes serious health issues and intake of pure alcohol is lethal. [Class-X – Science] 46 C2H5OH reacts with Sodium to form Sodium Ethoxide and Hydrogen When C 2 H 5 OH is heated with concentrated Sulphuric Acid at 443 K, it is dehydrated to Ethene Ethanoic Acid (CH3COOH) / Acetic Acid : *5-8% solution of acetic acid in water is called vinegar. *Pure acetic acid is called glacial acetic acid. 47 [Class-X – Science] 5 NaOH Sodium ethanoate and water. 5 2 1 3 4 H2O Esterification Carboxylic acids react with alcohols in presence of few drops of concentrated sulphuric acid as catalyst and form sweet smelling compounds called ester. conc. C 2 H 5OH CH 3COOH CH 3COOC 2 H 5 H SO ethanol of ester 2 ethanoic acid 4 ethyl ethanoate Hydrolysis On heating with an acid or a base the ester forms back the original alcohol and carboxylic acid. [Class-X – Science] 48 CH3COO CH2CH3 + NaOH CH3COONa + CH3-CH2OH CH3COO CH2CH3 Dil.H 2 SO 4 HEAT CH3COOH + CH3-CH2OH *Alkaline hydrolysis of ester is also called saponification. Soaps and Detergents – Soap is sodium and potassium salt of carboxylic acids with long chain. – Soaps are effective with soft water only and ineffective with hard water. – Detergents are ammonium or sulphonate salts of carboxylic acids with long chain. They are effective with both soft as well as hard water. An ionic part (hydrophilic) and a long hydrocarbon chain (hydrophobic) part constitutes the soap molecule. Structure of a Soap molecule. Cleansing Action of Soaps – Most dirt is oily in nature and the hydrophobic end attaches itself with dirt, while the ionic end is surrounded with molecules of water. This result in formation of a radial structure called micelles. 49 [Class-X – Science] – An emulsion is thus formed by soap molecule. The cloth needs to be mechanically agitated to remove the dirt particles from the cloth. – Scum : The magnesium and calcium salts present in hard water reacts with soap molecule to form insoluble products called scum, thus obstructing the cleansing action. Use of detergents overcome this problem as the detergent molecule prevents the formation of insoluble product and thus clothes get cleaned. 1. How does an atom of carbon attain noble gas configuration? 2. Draw the electron dot structure of a molecule of water. 3. Define catenation. 4. The kerosene/gas stove used at home has inlets for air. Give reason. 5. Write only the balanced chemical equation for dehydration of ethanol by hot conc. sulphuric acid. 6. Write the number of covalent bonds present in propane. 7. Define the term: oxidising agent with an example 8. Write the formula and name of first member of ketone. 9. Would you be able to check if water is soft by using a soap? 10. Write the molecular formula of an alkyne containing 10 atoms of hydrogen. 1. Define saponification. Write a chemical equation for it. 2. Covalent compounds generally don't conduct electricity. Why? [Class-X – Science] 50 3. Specify the condition in which ethanol undergo oxidation to form ethanoic acid. Write the chemical equation. 4. Define isomerism. Draw the structures of the two isomers of butane. 5. Identify the functional group present in the following compounds: HCOOH, HCHO, CH3Br and C10H21OH. 6. Why is ethanoic acid called as glacial acetic acid. Write the equation of the reaction that takes place when ethanoic acid reacts with ethanol in the presence of conc. H2SO4. 7. Draw that structures of the following compounds – (a) methanoic acid (b) pentanal. 8. Why are carboxylic acids called as weak acids? Name the alcohol which produces methanoic acid on oxidation. 9. (i) Which property of ethanol makes it suitable for preparing medicines such as tincture iodine, cough syrup and other tonics. (ii) What is the function of concentrated sulphuric acid in the formation of ethane from ethanol? 10. Define esterification. Explain with an example. 1. What is a homologous series? Write any two characteristic features of any homologous series using one example. 2. Write any three differences between soaps and detergents. 3. Write the main difference between addition and substitution reactions. Which reaction is commonly used in the hydrogenation of vegetablealso. 1. Differentiate between ethanol and ethanoic acid on the basis of any three physical properties and two chemical properties. 51 [Class-X – Science] 2. An organic compound 'A' is used as a preservative in pickles and has molecular formula C2H4O2. This compound reacts with ethanol to form a sweet smelling compound 'B'. (i) Identify the compound 'A' and write the chemical formula and chemical name. (ii) Write the chemical equation for its reaction with ethanol to form compound 'B'. (iii) Write any two uses of compound 'B'. (iv) Which gas is produced when compound 'A' reacts with washing soda? Write the balanced chemical equation (v) How can vinegar be obtained from compound 'A'? CARBON AND ITS COMPOUNDS IN BRIEF – Carbon is a versatile non-metal. – Carbon atom like atoms of other non-metals like oxygen, nitrogen, hydrogen and chlorine shares electrons. – Carbon forms large number of compounds due to catenation and tetravalency. – Carbon can form single, double and triple covalent bonds. – The compounds of hydrogen and carbon are called hydrocarbons, which can be saturated or unsaturated. – Structurally hydrocarbons can have straight chain, branches or cyclic structure. – Difference in structural arrangement of same molecule gives rise to isomerism. – In a hydrocarbon, a heteroatom can replace the hydrogen atom and imparts it chemical properties. [Class-X – Science] 52 – Homologous series is a series of compounds with same general formula and same chemical properties but different physical properties. – Carbon based compounds are excellent fuels. – Ethanol is an important industrial compound. It reacts with reactive metals and is also dehydrated to ethene. – Ethanoic acid is another important compound. It combines with ethanol to form sweet smelling esters. – Soaps and detergents are used as cleansing agents. Detergents efficiently cleanses with soft and hard water. 53 [Class-X – Science] CHAPTER – 5 PERIODIC CLASSIFICATION OF ELEMENTS Elements : Substances containing atoms of only one type. e.g. Na, Au, Mg etc. – There are around 118 elements known to us. Elements are classified to make the study easy. I. Dobereiner’s Traids : When the elements were written in order of increasing atomic masses the atomic mass of the middle was the average of the atomic mass of the other two elements. e.g. Elements Atomic Mass Ca 40.1 Sr 87.6 Ba 136.3 Limitations : Only three triads were recognised from the elements known at that time. Atomic mass of an element is the relative mass of its atom as compared with the mass of a Carbon-12 atom taken as 12 units II. Newland’s Law of Octaves – Based on increasing atomic mass of elements. – When elements are arranged it was found that every eighth element had properties similar to that of the first. e.g properties of sodium and Lithium are the same. [Class-X – Science] 54 Limitations – Applicable only upto Calcium – Properties of new elements couldn’t fit in it. – In some cases properties of the elements were not same as defined by octave. – Worked well only with lighter elements. III. Mendeleev's Periodic Law : The properties of elements are the periodic function of their atomic mass. Mendeleev's periodic table based on the chemical properties of elements. It contains vertical columns called groups and horizontal rows called periods. Achievements of Mendeleev’s Periodic table – Elements with similar properties could be grouped together – Some gaps were left for the undiscovered elements. – Noble gases could be placed without disturbing the existing order. Limitations – No fixed position for hydrogen – No place for isotopes – No regular trend in atomic mass. IV. Modern Periodic Table Modern Periodic Law : Properties of elements are a periodic function of their atomic number. – Atomic Number – denoted by Z and equals to the no. of protons in the nucleus of an atom. 55 [Class-X – Science] – Modern periodic table contains 18 vertical columns known as groups and 7 horizontal rows known as periods. – Elements in a group have the same number of valence electrons – No. of the shells increases as we go down the group. – Elements in a period have same number of shells. – Each period marks a new electronic shell getting filled. – No. of elements placed in a particular period depends upon the fact that how electrons are filled into various shells. – Maximum no. of electrons that can be accommodated in a shell depend on the formula 2n2 where n is the no. of the given shell. e.g. K shell – 2 × (1)2 = 2 elements in the first period L shell – 2 × (2)2 = 8 elements in the second period. – Position of the element in the periodic table tells about its reactivity. Trends in the Modern Periodic Table – VALENCY : No. of valence electrons present in the outermost shells. Valency remains the same down a group but changes across a period. – ATOMIC SIZE : Atomic size refers to radius of an atom. – Atomic size or radius decreases in moving from left to right along a period due to increase in nuclear charge – Atomic size increases down the group because new shells are being added as we go down the group. METALLIC CHARACTER : Metallic character means the tendency of an atom to lose electrons. – Metallic character decreases across a period because the effective nuclear charge increases that means the tendency to lose electrons decreases. – Metals are electropositive as they tend to lose electrons while forming bonds. [Class-X – Science] 56 – Metallic character increases as we go down a group as the effective nuclear charge is decreasing. Non metals are electronegative. They tend to form bonds by gaining electrons. – Metals are found on the left side of the period table while non-metals are towards the right hand side of the periodic table. – In the middle we have semi-metals or metalloid because they exhibit some properties of both metals and non metals. – Oxides of metals are basic in nature while oxides of non-metals are acidic in nature. (Refer the table given on side page) Gradation in Periodic Properties S. Property Variation No. across period Reason Variation along group Reason 1. Atomic size Decreases Due to increase in nuclear charge Increases due to addition of new shells. distance between outer most electron and nucleus increases due to addition of new shells. 2. Metallic Character Decreases due to increase in effective nuclear charge, tendency to lose valence electrons decreases. Increases decrease in effective nuclear charge experienced by valence electrons Tendency to lose electrons (metallic character) increases. 3. Non-Metallic Increases Character (electronegativity) due to increase Decreases in effective nuclear charge tendency to gain electrons increases 57 due to decrease in effective nuclear charge experienced by valence electron (due to addition of new shell), tendency to gain electrons decreases. [Class-X – Science] Very Short Answer type Questions (1 Mark) 1. Write down three elements which represent Dobereiner’s triad. 2. Write down two drawbacks of Newland’s law of octaves. 3. Which important property did Mendeleev used to classify the elements in his periodic table. 4. Explain why the number of elements in the third period is 8? 5. Name two elements you would expect to show chemical reactions similar to lithium. 6. Define Isotopes. 7. What was the need for classification of elements? 8. Name two elements that have only two electrons in their outermost shell. 9. How many vertical columns and horizontal rows are there in modern periodic table, What is the special name assigned to them? 10. Name the element having electronic configuration 2, 8, 3. What is its Valency? Short Answer type Questions (2 Marks) 1. Why He, Ne and Ar are called inert gases? 2. Which one has greater atomic size – Cl or Br? Why? 3. What were the drawbacks of Mendeleev’s periodic table? Write any two. 4. How does the tendency to lose electrons change in a group and why? 5. Justify the statement – Atomic size of an element decreases along a period whereas increases down the group. [Class-X – Science] 58 6. What is the metallic character of an element? How does it vary as we go down a group? Give reason for this variation. 7. How does electronegativity of an element change as you go down a group and across a period? Give reason for the variation. Long Answer Type Questions (3 Marks) 1. How do we calculate the valency of an element from its electronic configuration? – How does the valency vary in a period? – How does the valency vary in going down a group? 2. Study the variation in the atomic radii of elements given below and arrange them in an increasing order Na 186 Li 152 Rb Cs K 246 262 231 (ii) Name the element which has the smallest and the largest atoms. (iii) How does the atomic size vary as we go down a group. Give reason for your answer. 3. Four elements ABCD along with their electronic configurations are given below Elements – Electronic Configuration – A B C D 2, 1 2, 8 2, 8, 1 2, 8, 8 Now answer the following questions : 4. Why did Mendeleev choose formulae of compounds as the basis for deciding the position of an element in his table? Why did he leave some gaps in his periodic table? Name two elements which were discovered later but filled in the gaps left by Mendeleev. a) Which two elements belong to the same period. 59 [Class-X – Science] b) Which two elements belong to the same group c) Which element out of A and C is more reactive and why? Long Answer Type Questions (5 Marks) 1. Write down five major differences between Mendeleev periodic table and modern periodic table. 2. Examine elements of the third period and classify them as metals and non metals. (ii) On which side of the table do you find metals and why. (iii) On which side of the table do you find the non-metals and why? [Class-X – Science] 60 CHAPTER – 6 LIFE PROCESSES All living things perform certain life processes like growth, excretion, respiration, circulation etc. The basic functions performed by living organisms for their survival and body maintenance are called life process. Basic life processes are : Nutrition, Respiration, Transportation, Excretion etc. Kinds of nutrition in which organisms can synthesize their own food. Kinds of nutrition in which organisms do not possess the ability to synthesize their own food. They depend on autotrophs for their food supply directly or indirectly. E.g. Green Plants E.g. Animals, Fungi Autotrophic Nutrition Autotrophs : The organisms which can make their own food are called autotrophs (green plants). Photosynthesis : The process by which green plants make their own food with the help of CO2 and H2O in the presence of chlorophyll and sunlight is also called photosynthesis. Sunlight 6CO 2 6H 2O C6 H12O6 6O 2 Chlorophyl Glucose Raw Materials for Photosynthesis : CO2 and H2O 61 [Class-X – Science] Site of Photosynthesis : Chloroplast in the leaf. Chloroplast contain chlorophyll. (green pigment). Main Events of Photosynthesis 1. Absorption of Sun light energy by chlorophyll 2. Conversion of light energy into chemical energy and splitting (breaking) of water into hydrogen and oxygen by light energy. 3. Reduction of CO2 to carbohydrates. Stomata : Tiny pores present on the surface of the leaves. Functions of Stomata (i) Exchange of gases O2/CO2 (ii) Loses large amount of water [water vapour] during transpiration and helps in upflow of water Chloroplast Stomatal pore Guard cells it ), [Class-X – Science] 62 Nutrition in Animals Nutrition in Animals Ingestion Digestion Absorption Assimilation Egestion Nutrition in Amoeba (i) Amoeba move with the help of pseudopodia (extension of cell membrane) (ii) Food vacule is formed (iii) Food is digested in the food vacuole (iv) Undigested food is thrown out. Nutrition in Human Beings : The human digestive system comprises of alimentary canal and associated digestive glands. 63 [Class-X – Science] 1. Mouth Salivary glands Secrete Secrete saliva (change starch int sugar). Salivary amylase Teeth (Chewing/grinding of food) Tongue (Rolling, tasting of food) 2. Oesophagus Takes food from mouth to oesophagus by peristatic movements. (contraction and expansion of ailimentary canal) Gastric Juices 3. Stomach Pepsin (breaks down) Protein HCl Makes medium acidic Mucus (Protects inner lining of stomach 4. Small Intestine Liver Secretes bile Pancreas secrete pancreatic juice Intestinal enzyme Carbohydrate Glucose Fats Fatty acid + Glycerl Protein Amino acid Pancreatic Juice Lipase Trypsin Fatty acid Proteins Peptones Emulsified Fats Glycerol Large fat globules Bile Juice (emulsification) Small fat globules 5. Large Intestine (absorbs excess water) 6. Rectum (Temporary collection of waste) 7. Anus (helps in egestion) [Class-X – Science] 64 HUMAN DIGESTIVE SYSTEM 65 [Class-X – Science] RESPIRATION Respiration Involves (i) Gaseous exchange : Intake of oxygen from the atmosphere and release of CO2 Breathing (ii) Breakdown of simple food in order to release energy inside the cell Cellular Respiration Breakdown of Glucose by various pathways Glucose C6H12O6 ( in * * * * mu sc les ) Respiration Takes place in the presence of oxygen Occurs in mitochondria End products are CO2 and H2O More amount of energy is released (38 ATP) [Class-X – Science] 66 * * * * Takes place in the absence of oxygen Occurs in cytoplasm End products are alcohol or lactic acid. Less amount of energy is released. (2 ATP) Human Respiratory System : Passage of air through the respiratory system. Nostril Nasal Passage Nasal Cavity Pharynx Larynx Trachea Bronchi Lungs Bronchioles Alveolar sac Blood capillaries Mechanism of Breating 1. During inhalation the thoracic cavity (chest cavity) expands 1. Thoracic cavity contracts 2. Ribs lift up 3. Diaphragm becomes dome shaped 3. Diaphragm become flat in shape 4. Volume of lungs decreases and air exits from the lungs. 2. Ribs move downwards 4. Volume of lungs increases and air enters the lungs 67 [Class-X – Science] Exchange of Gases between alveolus, blood and tissues. (capillaries) (capillaries) (in alveoli) Terrestial Organism – use atmospheric oxygen for respiration Aquatic Organisms – use oxygen dissolved in water. Respiration in Plants : Respiration in plants is simpler than the respiration in animals. Gaseous exchange occur through 1. Stomata in leaves 2. Lenticels in stems 3. General surface of the roots. [Class-X – Science] 68 Transportation (i) Human beings like other multicellular organism need regular supply of food, oxygen etc., This function is performed by circulatory system or Transport system. (ii) The circulatory system in human beings consists of : A Pumping Organ Heart Deoxygenated Blood (from body) Blood vessels - Arteries & Veins Vena Cava A circulatory medium Blood & Lymph Right Atrium Right Ventricle Lungs Body Parts Blood Circulation in Human Heart via AORTA Left Ventricle Left Atrium Oxygenated blood AORTA Section view of the Human Heart 69 [Class-X – Science] Double Circulation : Blood travels twice through the heart in one complete cycle of the body. • Pulmonary circulation : blood moves from the heart to the hugs and back the heart. • Systemic circulation : blood moves from the heart to rest of the body and back to the heart. Blood (A fluid Connective Tissue) Solid Component Blood Corpuscles R.B.C.s Blood Platelets Liquid Component PLASMA W.B.C. Lymph - a yellowish fluid that escapes from the blood capillaries into the intercellular spaces. Lymph flows from the tissues to the heart assisting in transportation and destroying germs. Blood Vessels Arteries 1. 2. 3. 4. 5. Veins Carry Oxygenated blood from heart to body part except pulmonary Artery Also called distributing Vessel Thick and elastic Valves absent Deep seated 1. 2. 3. 4. 5. [Class-X – Science] 70 Carry deoxygenated blood from body parts to heart except pulmonary vein. Also called collecting Vessel. Thin and Less elastic. Valves present to prevent back flow of blood. Superficial Transportation in Plants : There are two main conducting tissues in a plant. (a) Xylem (b) Phloem. Conducting Tissue Xylem Phloem 1. Carries water & minerals from the roots to other part of the plant 2. No energy is used. 1. Carries product of photosynthesis from leaves to the other part of the plant. 2. Energy is used from ATP Transpiration is the process by which plants lose water in the form of vapours. Role of Transpiration 1. Absorption and upward movement of water and minerals by creating PULL. 2. Helps in temperature regulation in Plant. Translocation : Transport of food from leaves (food factory) to different part of the plant is called Translocation. Excretion in human beings : The process of the removal of the harmful metabolic wastes from the body is called excretion. Excretory system of human beings includes : (i) A pair of kidney (ii) A Urinary Bladder (iii) A pair of Ureter (iv) A Urethera 71 [Class-X – Science] Process of Excretion – Renal artery bring in blood containing waste substances to the kidneys. – Kidney filters blood. – Urine produced in the kidneys passes through the ureters into the urinary bladder where it is stored until it is released through the urethera. Function of Kidney : It is remove waste product from the blood ie, urea which is produced in the liver. Nephron : Each kidney has a large number of filtration units called nephrons. – Nephron is the structural and functional unit of Kidney. Structure of Nephron Mechanism of Urine Formation : The Urine formation involves three steps: 1. Glomerular Filtration : Blood is filtered from the glomerulus into Bowman Capsule of the nephron. This filtrate passes through the tubules of the nephron. [Class-X – Science] 72 2. Tubular reabsorption : Now, useful substances from the filtrate like Na+, k+, glucose, amino acids etc. are reabsorbed by the capillaries surrounding the nephron into the blood. 3. Secretion : Urea, extra water and salts are secreted into the tubule which open up into the collecting duct & then into the ureter. – Haemodialysis : The process of purifying blood by an artificial kidney. It is meant for Kidney failure patient. Excretion in Plants 1. Oxygen released during photosynthesis. 2. H2O by transpiration 3. Wastes may be stored in leaves, bark etc. which fall off from the plant. 4. Waste products stored as gums, resin in old Xylem 5. Plants excrete some waste into the soil around them. Very Short Answers (1 Mark) 1. State one difference between autotrophic and heterotrophic mode of nutrition. 2. Define peristaltic movement. 3. What is the role of saliva in the digestion of food? 4. Name the tissue that transports water and minerals in plants. 5. What is the role of acid in our stomach? 6. What is emulsification? 7. Name the cell organelle in which photosynthesis occur. 8. Name the largest artery in the human body. 73 [Class-X – Science] 9. Define transpiration 10. What is the structural and functional unit of kidney called? Short Answers (2 or 3 Marks) 1. How is small intestine designed to absorb digested food? 2. What are stomata? Draw a labelled diagram of stomata. 3. Write the equation for the process of breakdown of glucose in a cell (i) in the presence of oxygen (ii) in the absence of oxygen. 4. Write the difference between inhalation and exhalation. 5. List the three events which occur during photo synthesis. 6. How does transpiration help in upward transport of substances. 7. Write the functions of the components of blood. 8. Why is small intestine longer in herbivores than in carnivores? 9. Explain the cause of cramps after excessive physical exercise. 10. Why is the rate of breating in aquatic organisms much faster than that seen in terrestrial organisms. Short Answers (3 Marks) 1. Describe the process of double circulation in human beings. 2. What are the methods used by plants to get rid of their waste products? 3. Give reason for the following : (i) Arteries are thick walled blood cessels. (ii) Veins are thin walled blood vessels (iii) Veins have valves in them. Long Answers (5 Marks) 1. Explain the process of digestion of food in mouth stomach and small intestine in human body. Draw a well labelled diagram of human digestive system. [Class-X – Science] 74 2. Draw a diagram showing Human Respiratory system. Label the following parts (i) Alveolus (ii) Trachea (iii) Bronchus (iv) Lungs 3. Draw a well-labelled diagram of nephron. Explain the mechanism of urine formation in human beings. 75 [Class-X – Science] CHAPTER – 7 CONTROL AND CO-ORDINATION Living organisms respond to various stimuli like heat, light, cold, touch, pressure etc. Example : Withdrawal of hand on touching a hot object. Control and Coordination in Animals It is brought about in all animals with the help of two main systems (a) Nervous System (b) Endocrine System Nervous System Functions (i) To receive the information from environment (ii) To receive the information from various body parts. (Stimuli Response) (iii) To act accordingly through muscles and glands. Stimulus : Any change in environment to which the organisms respond is called stimulus. E.g., touching a hot plate. Response : The reaction of our body to a stimulus. E.g. withdrawal of our hand on touching hot plate. Receptors : Are specialised tips of some nerve cells that detect the information from the environment. [Class-X – Science] 76 Receptors are Sense Organs Photo receptors Thermoreceptors Olfactory Eyes (Skin) Receptor (Nose) Hearing/ Balance of the body Visual Stimulus Pain Touch Heat Smell Detection Gustatory Receptor (Tongue) Taste Detection Neuron : It is the structural and functional unit of nervous system. Neuron (3 main parts) I II III Dendrite Cell body and Axon Synapse Information is acquired Information travels as an electrical impulse Nucleus Nerve ending Dendrite Axon Cellbody Structure of neuron 77 [Class-X – Science] Synapse : The point of contact between the terminal branches of axon of one neuron with the dendrite of another neuron is called synapse. Reflex action is an automatic response of the body to a stimulus. e.g. withdrawal of hand, knee jerk etc. on touching a hot plate. Reflex arc : The pathway taken by nerve impulses in a reflex action is called reflex arc. Voluntary means it is under the control of a person (e.g. writing) Involuntary means it is not under the control of a person. (e.g. heartbeat) [Class-X – Science] 78 Human Brain : It is enclosed in cranium (brain box) and is protected by cerebrospinal fluid which acts as a shock absorber. Human brain has three major parts or regions : (a) Forebrain, (b) Mid Brain, (c) Hind Brain. (a) Forebrain Most complex/specialized part of the brain is CEREBRUM Functions 1. Thinking part of the brain 2. Control the voluntary actions. 3. Store information (Memory) 4. Centre associated with HUNGER 5. Receives sensory impulses from various body parts and integrates it (b) Mid Brain : It connects the forebrain with the hindbrain. (c) Hind Brain CEREBELLUM i) Maintains posture and balance of the body. ii) Control body movement. MEDULLA Controls involuntary actions eg. blood pressure, salivation, vomiting PONS Involuntary action, regulation of respiration 79 [Class-X – Science] PROTECTION OF BRAIN AND SPINAL CORD Brain : Brain is protected by a fluid called cerebrospinal fluid which acts as shock absorber. Spinal Cord : Spinal Cord is enclosed in Vertebral column. Coordination in Plants Movement in Plants Movement dependent on growth Movement independent of growth [immediate response to stimulus] eg. dropping of leaves of Touch-me-not plant on touching it (Thigmotropism) Tropic movements [directional movements in response to stimulus] Phototropism Movement towards light Geotropism Chemotropism Movement Movement towards gravity towards Chemicals/ (growth of pollen tube towards ovule) Plant Hormones [Class-X – Science] 80 Hydrotropism Movement towards / water Are chemical compounds which help to coordinate growth, development and responses to the environment. Plant Hormones : Main plant hormones are : (a) Auxin : [Synthesized at shoot tip] Function : Helps in growth Phototropism : more growth of cells towards light. (b) Gibberellin : Helps in the growth of the stem (c) Cytokinins : Promotes cell division (d) Abscisic acid : Inhibits growth, cause wilting of leaves. (Stress hormone). It promotes the closing of stomata (during adverse drought condition) their by reducing the water loss. HORMONES IN ANIMALS Hormones : Hormones are the chemical substances secreted by the endocrine glands and transmitted by the blood to the tissues on which it has a specific effect. 81 [Class-X – Science] S. No. Hormone Endocrine Gland Location Functions 1. Thyroxin Thyroid Neck/ Throat region Regulation of metabolism of carbohydrates, fats and proteins. 2. Growth hormone Pituitary (master gland) Mid brain Regulates growth and development. 3. Adrenaline Adrenal Above both kidneys 4. Insulin Pancreas Below stomach Regulation (increasing) of blood pressure, heart beat, carbohydrate metabolism (during emergency). Reduces and regulates blood sugar level. 5. SEX Testosterone in Males Oestrogen in females Testes Genital/ lower abdomen area Ovaries Changes associated with puberty (Sexual maturity) Iodised Salt is Necessary because thyroid gland needs iodine to make thyroxine which helps in regulating the metabolism of carbohydrates, fats and proteins. Deficiency of iodine cause a disease called goitre. Diabetes Cause : It is due to deficiency of Insulin hormone secreted by Pancreas that is responsible to lower/control the blood sugar levels. Treatment : Common diabetes can be controlled by medicine but in severe cases. Injections of insulin hormone are given to the patients. Feedback Mechanism The excess or deficiency of hormones has a harmful effect on our body. [Class-X – Science] 82 Feedback mechanism makes sure that hormones are secreted in precise quantities and at right time. SWITCH OFF Feedback sent Sugar level in the blood rises Detected by cells of Pancreas Synthesis insulin Blood sugar level falls (like a float in watertank) Stop secreting more insulin Very Short Answers (1 Mark) 1. Where is auxin synthesized in plants? 2. Which gland is known as Master gland? 3. Name the hormone that regulates blood sugar level. 4. What is synapse? 5. What are tropic movements? Give one examples 6. Which part of brain is responsible for maintaining posture and balance of our body? 7. Which hormone has inhibiting effect on growth of plants. 8. What is phototropism? 9. What are the components of central Nervous System? 10. What happens at synapse between two neurons? Short Answers (2 Marks) 1. Draw diagram of neuron and label cell body, dendrites and axon. 83 [Class-X – Science] 2. What is reflex arc? Explain with the help of a flow-chart. 3. Mention one function of each of the following (i) Cerebellum (ii) Pons. 4. What is the cause of diabetes? How can it be controlled? 5. Why is it advisable to use iodised salt? 6. Name the different receptors present in our body and write their functions. 7. What are plant hormones? Name a plant hormone that promotes growth in plants. 8. What are sensory and motor neurons? Write their functions. 9 Why is Abscisic acid called a stress hormone? 10. Explain bending of a plant stem towards light by the action of auxin hormone. Short Answers (3 Marks) 1. What is the significance of tropic movement in plants? Explain any two types of tropic movements. 2. (i) What are endocrine glands? (ii) Name a gland which has both endocrine and exocrine functions. Also write its endocrine and exocrine secretions. 3. Which hormone is known as emergency hormone in our body? How does it help in coping during emergency? Long Answers 1. (5 Marks) (a) Define hormones. [Class-X – Science] 84 (b) Name any four endocrine glands and the hormones secreted by them. (c) Name the hormones required for the following : (i) development of moustache and beard in male (ii) Lowering of blood glucose. 2. Mention the functions of : (a) Fore brain (b) Mid brain (c) Hind brain 85 [Class-X – Science] CHAPTER – 8 HOW DO ORGANISM REPRODUCE Reproduction is the process by which living organisms produce new individuals similar to themselves. Reproduction ensures continuity of life on earth. It involves continuation of characters from the parents to daughter cells [by Copying of DNA (Deoxyribose Nucleic Acid) molecules present in the chromosomes of the cell]. Copying of DNAs is also not a foolproof exercise, even minute changes bring about Variation in the blue print of the offsprings. Variations help the species to withstand drastic environmental changes, thus save the species from becoming extinct and promotes its survival for a longer time. REPRODUCTION Asexual Reproduction Sexual Reproduction 1. A single parent is involved 1. Both Parents involved 2. Gametes not formed 2. Gametes are formed 3. Progeny is Identical to parent e.g. Fission in Amoeba 3. Progeny is only genetically similar to the parent but not identical Asexual Reproduction is extremely useful as a mean of rapid multiplication. It is common in lower plants and animals. MODES OF ASEXUAL REPRODUCTION 1. FISSION : the parent cell divides/splits into two daughter cell-Binary Fission; splits into many cells-multiple Fission. [Class-X – Science] 86 FISSION Binary Fission The parent cell divides into two equal halves (daughter cells) Multiple Fission The parent cell divides into many daughter cell simultaneously. E.g. Amoeba Eg. Plasmodium cytoplasm divides Daughter Ameobae nucleus nucleus lengthens 2. BUDDING : A bud develops as an outgrowth on parent body due to repeated cell division at a specific site. These buds detach from the parent body when they mature. E.g. Hydra, yeast. 3. SPORE FORMATION : Spores are small, bulb like structure which are covered by thick walls that protect them until they come in contact with suitable condition. Under favourable conditions, they germinate and produce new organism. 87 [Class-X – Science] 4. FRAGMENTATION : It is the accidental process when the broken pieces of an organism (fragments) grows into a complete organism. Eg. fragmentation in spirogyra 5. REGENERATION : When the simple animals like Hydra Planaria develop a new individual from their broken older part it is known as regeneration. It is carried out by specialised cells which divide and differentiate to form the complete individual. [Class-X – Science] 88 Vegetative Propagation A mode of reproduction in which reproduction takes place from the vegetative parts like the stem, root, leaves. Methods of Vegetative Propagation Natural 1. By Roots : E.g. adventitious roots of Dahlias 2. By Stems : E.g. Potato (tuber), ginger (rhizome) 3. By Leaves : E.g. leaves of bryophyllum bear adventitious buds (in the notches of leaf margin) which develop into new plants. Artificial 1. Grafting : E.g. Mango. 2. Cutting : E.g. Rose 3. Layering : E.g. Jasmine 4. Tissue adture : E.g. Orchids, Ornamental Plants. Benefits of Vegetative Propagation 1. Plants can bear flowers, fruits earlier than those produced from seeds. 2. Growing plants like Banana, orange, rose, jasmine that have lost the capacity to produce seeds. 3. Genetical similarity is maintained in the plants. 4. Helps in growing seedless fruits. 5. Cheaper and easier method of growing plants. Sexual Reproduction When reproduction takes place as a result of fusion of two gameets, one from each parent, it is called sexual reproduction. 89 [Class-X – Science] The process of fusion of male and female gametes is called fertilization. The formation of gamets involves exchange of chromosomal (genetic) fragments between homologous chromosomes causing genetic recombination which leads to variation. Sexual Reproduction in Plants It occurs mostly in flowering plants. In fact flowers are the reproductive organ of plants. FLOWERS Bisexual Flowers Both male and female reproductive part i.e., stamen & carpel are present. Unisexual Flowers Either male or female reproductive part is present. Eg. Papaya, Watermelon Stigma Anther (Carpet) Stamen Eg. Hibiscus, mustard A typical flower consists of four main whorls namely calyx (sepals), Corolla (Petals), Androecium (Stamens) and Gynoecium (Carpels). [Class-X – Science] 90 Reproductive Part of Flower STAMEN (male part) Filament CARPEL (female part) Anther MEIOSIS Pollen grain (male gamet) (n) Style Ovary Stigma Egg cell (ovule) [n] Pollen grains of a flower transfer to the stigma of the carpel of the same flower (Self-Pollination) or to the stigma of carpel of the another flower (Cross-Pollination). This transfer of pollens is achieved by agent like wind, water or animals. After Pollination, a pollen tube grows out of pollen grains, throughwhich male germ cell reaches the ovary and fuses with the female germ cell. Fertilization : The fusion of male and female gamete is called fertilization. It occurs inside the ovary. Zygote is produced in this process. Zygote divides several times to form an embryo within the ovule. The ovule develops a tough coat and is converted into a seed. 91 [Class-X – Science] Ovary grows rapidly and ripens to forms a fruit, while the seed contains the future plant or embryo which develops into a seedling under suitable condition. This process is known as Germination. Reproduction in Human Beings Humans use a Sexual Mode of reproduction. It needs sexual maturation which includes creation of the germ cells ie, egg (ova) in the female and sperm in the male partener & this period of sexual maturation is called Puberty. Male Reproductive System The formation of male germ cell (sperms) takes place in the testes (male reproductive organ) A pair of testes are located inside scrotum which is present outside the abdominal cavity. Scrotum has a relatively low temperature needed for the production of sperms by testes. Testes release a male sex hormone called testosterone and its function is to: 1. Regulate the production of sperm 2. Bring about changes in appearance seen in boys at the time of puberty. The sperms along with the secretion of prostate gland and seminal vesicle, together constitute semen, which is released and made to enter into the female genital tract during Copulation. Female Reproductive System The female germ cells or eggs are produced in the ovaries. (located in both side of abdomen). When a girl is born, the ovaries already contain thousands of immature eggs. [Class-X – Science] 92 At puberty, some of these eggs start maturing. One egg is produced every month by one of the ovaries. The Egg is carried from the ovary to the womb through a fallopian tube. These two fallopian tube unite into an elastic bag like structure known as uterus. The Uterus opens into the vagina through the cervix. Fertilization occurs in the fallopian tube of female genital tract. The fertilized egg also called zygote (2n) gets implanted in the lining of the uterus, and start dividing. Actually uterus is richly supplied with blood to nourish the growing embryo. If zygote is not formed, the inner wall of uterus breaks which causes bleeding through vagina. This process is called MENSTRUATION. It occurs at a regular interval of 28 days. The Embryo gets nutrition from the mother's blood with the help of a special tissue called PLACENTA. It provides a large surface area for glucose and oxygen to pass from the mother to the embryo. Similarly the wastes from developing embryo are removed to mother's blood through placenta. The time period from fertilization upto the birth of the baby is called Gestation Period. In humans, it is about nine months (36 weeks). The sexual cycle (Menstruation) in a woman continues upto the age of 45-50 years. After that the ovaries do not release egg. This stage is 93 [Class-X – Science] called Menopause. It also marks the end of the reproductive life of a woman. Female sex hormones are oestrogen and progesterone which are produced by ovary. Reproductive Health Reproductive Health means a total well-being in all aspects of reproductive, i.e., physical emotional, social and behavioural. Contraception : It is the avoidance of pregnancy. It can be achieved by preventing the fertilization of ova. METHODS OF CONTRACEPTION PHYSICAL BARRIER SURGICAL METHOD CHEMICAL METHOD IUCD To prevent union of sperm & egg. Also called sterilization in Vasectomy, the vas deferens of male is blocked to prevent sperm transfer. Oral contraceptive (OCs) - changes the hormonal balance to check the egg release in females. OCs c aus e si de effect. Intrauterine contraceptive device Co pp e r- T o r loop is placed in uterus to prevent pregnancy. Use of condoms, Diaphragm & cervical caps. In Tub ec tomy, t he fallopian tube of female is blocked to prevent egg to reach uterus. Healthy society needs a balanced sex ratio that can be achieved by educating people to avoid malpractices like female foeticide & prenatal sex determination. Sexually Transmitted Disease (STDs) VIRAL STDs Eg. H.I.V. - AIDS Warts [Class-X – Science] Bacterial STDs Eg. Syphilis & Gonorrhoea 94 (1 Mark) 1. Where is the DNA present in the cell? 2. What is a bisexual flower? Give one example. 3. Write suitable condition necessary for seed germination.. 4. Write the function of the secretions of seminal vesicle and prostate gland. 5. Name the part of female reproductive system where the egg is fertilized. 6. How does the chemical method help in preventing pregnancy? 7. Name the floral parts of a plant that develop into (i) Fruit (ii) Seeds 8. What method will you use for growing Jasmine and Rose (plants)? 9. Name the hormones responsible for secondary sexual characters in (i) Girls (ii) Boys. 10. What is Gestation period? (2 Marks) 1. What is the importance of DNA copying in reproduction. 2. Write any two differences between sexual and asexual reproduction. 3. Why is vegetative propagation practised for growing some types of plants? 4. Distinguish between male & female gamete. 5. Write two important functions of testosterone. 6. What is placenta? Also write its two functions. 95 [Class-X – Science] 7. Explain regeneration. 8. With the help of flow diagram trace the path of sperm from the site of its formation to outside the body of males. 9. What is tissue culture in plants? 10. State the role of reproduction in providing stability to populations of various species. (3 Marks) 1. Draw a well labelled diagram of human female reproductive system. Explain the menstrual cycle of female. 2. Draw a labelled diagram to explain fertilization in higher plant. 3. (i) Give two reasons for avoiding frequent pregnancies by women. (ii) Explain the following methods of contraception giving one example of each. (a) Barrier method. (b) Surgical method. 4. In human females, what happens when (i) egg is fertilised (ii) egg is not fertilised? 5. Give two examples each of sexually transmitted diseases (STDs) caused by (i) Virus; (ii) bacteria. (5 Marks) 1. Trace and explain the steps involved in the formation of seed starting from pollination. 2. List any four modes of asexual reproduction. Give one example of each. Explain any two modes of asexual reproduction. [Class-X – Science] 96 CHAPTER – 9 HEREDITY AND EVOLUTION Genetics : Branch of science that deals with Heredity and variation. Heredity : It means the transmission of features/ characters/ traits from one generation to the next generation. Variation : The differences among the individuals of a species/ population are called variations. Mendel and His Work on Inheritance Gregor Johann Mendel (1822&1884) : Started his experiments on plant breeding and hybridisation. He proposed the laws of inheritance in living organisms. Mendel was known as Father of Genetics Plant selected by Mendel : Pisum sativum (garden pea). Mendel used a number of contrasting characters for garden pea. (TABLE OF CONTRASTING CHARACTERS. SEVEN PARTS) CHARACTER DOMINANT RECESSIVE TRAIT TRAIT Flower colour Violet White Flower position Axial Terminal Seed colour Yellow Green Seed shape Round Wrinkled Pod shape Inflated Constricted Pod colour Green Yellow Height of plant Tall Dwarf/Short Seven pairs of contrasting characters in Garden Pea. 97 [Class-X – Science] Mendels Experiments : Mendel conducted a series of experiments in which he crossed the pollinated plants to study one character (at a time) Monohybrid Cross Cross between two pea plants with one pair of contrasting characters is called a monohybrid cross. Example : Cross between a tall and a draft plant (short). PARENT Tall plant ALLELIC PAIR OF GENES GAMETES TT T t Tt F1 GENERATION (first filial generation) GAMETES t T Gametes [Class-X – Science] 3:1 1:2:1 98 t All tall plants Tt F2 GENERATION Phenotypic ratio Genotypic ratio tt T SELF POLLINATION of F1 gametes Dwarf plant Tt T T t TT Tt tall tall Tt tt tall dwarf t inflated/full 99 [Class-X – Science] TT tt Both dominant traits Both recessive alleles Pure or homozygous conditon Tt One dominant, one recessive trait Hetrozygous condition - Hybrid Phenotypic ratio : 3:1 Genotypic ratio : 1:2:1 Phenotype Physical appearance [Tall or Short] Genotype Genetic make up [TT, Tt or tt] Observations of Monohybrid Cross 1. All F1 progeny were tall (no medium height plant (half way characteristic) 2. F2 progeny ¼ were short, ¾ were tall 3. Phenotypic ratio F2 – 3:1 (3 tall : 1 short) Genotypic ratio F2 – 1:2:1 TT : Tt : tt 1 : 2 : 1 Conclusions 1. TT and Tt both are tall plants while tt is a short plant. 2. A single copy of T is enough to make the plant tall, while both copies have to be ‘t’ for the plant to be short. 3. Characters/Traits like 'T' are called dominant trait (because it express itself) and ‘t’ are recessive trait (because it remains suppressed) Dihybrid Cross : A cross between two plants having two pairs of contrasting characters is called dihybrid cross. [Class-X – Science] 100 PARENT GENERATION ROUND GREEN SEEDS WRINKLED YELLOW SEEDS RRyy y rrYY rY GAMETES RrYy [round, yellow] F1 F1 RY Ry rY ry Rr Yy F1 gametes F1 Rr Yy RY Ry rY ry G A M E T E S RY RY RRYY Ry RRYy rY RryY ry RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy Selfing F1 gametes Phenotypic Ratio Round, yellow : 9 Round, green : 3 Wrinkled, yellow : 3 Wrinkled, green : 1 Observations 1. When RRyy was crossed with rrYY in F1 generation all were Rr Yy round and yellow seeds. 101 [Class-X – Science] 2. Self pollination of F1 plants gave parental phenotype and two mixtures (recombinants round yellow & wrinkled green) seeds plants in the ratio of 9:3:3:1 9 Round Yellow : 3 Round green : 3 Wrinkled yellow : 1 wrinkled green Conclusions 1. Round and yellow seeds are DOMINANT characters 2. Occurrence of new phenotypic combinations show that genes for round and yellow seeds are inherited independently of each other. SEX DETERMINATION Determination of sex of an offspring. FACTORS Responsible for Sex Determination Environmental In some animals the temperature at which the fertilised eggs are kept decides the gender. eg. in Turtle Genetic In some animals like humans gender or individual is determined by a pair of chromosome called sex chromosome XX – Female XY – Male Sex Chromosomes : In human beings there are 23 pairs of chromosome. Out of these 22 chromosomes pairs are called autosomes and the last pair of chromosome that help in deciding gender of that individual is called sex chromosome. XX – female XY – male [Class-X – Science] 102 Sex determination in Human beings PARENTS : FATHER XY GAMETES (Reproductive cells) Zygote formed after fusion of gametes X MOTHER XX Y X XX FEMALE XX FEMALE X XY MALE 50% probability of a female child offspring XY MALE 50% probability of a male child This shows that half the children will be boys and half will be girls. All children will inherit an X chromosome from their mother regardless whether they are boys or girls. Thus sex of children will be determined by what they inherit from their father, and not from their mother. EVOLUTION Evolution is the sequence of gradual changes which takes place in the primitive organisms, over millions of years, in which new species are produced. Situation-I Group of red beetles Colour variation arises during reproduction All beetles red except one that is green One beetle Green Reproduction Crows feed on red beetle Progeny beetles green No. of beetles reduces 103 [Class-X – Science] Crow could not feed on green beetles as they got camouflaged in green bushes Number of green beetles increases Situation 1 : Green beetles got the survival advantage or they were naturally selected as they were not visible in green bushes. This natural selection is exerted by crows resulting in adaptations in the beetles to fit better in their environment Situation-II Group of red beetles Reproduction All beetles are red except one that is blue Reproduces One blue beetle Reproduces Number of red beetle increases No. of blue beetle increases Crows can see both blue and red beetles and can eat them Number reduces but still red beetles are more and blue ones are few Suddenly elephant comes and stamps on the bushes But now beetles left are mostly blue. Situation 2 : Blue beetles did not get survivals advantage. Elephant suddenly caused major havoc in beetle population otherwise their number would have been considerably large. From this we can conclude that accidents can change the frequency of some genes even if they do not get survival advantage: This is called genetic drift and it leads to variation. [Class-X – Science] 104 SITUATION-III Group of red beetles Habitat of beetles (bushes) Suffer from plant disease Average weight of beetles decreases due to poor nourishment Number of beetles kept on reducing Later plant disease gets eliminated Number and average weight of the beetles increases again Situation 3 : No genetic change has occurred in the population of beetle. The population gets affected for a short duration only due to environmental changes. ACQUIRED AND INHERITED TRAITS Acquired Traits Inherited Traits 1. These are the traits which are developed in an individual due to special conditions 1. These are the traits which are passed from one generation to the next. 2. They cannot be transferred to the progeny 2. They get transferred to the progeny. 3. They cannot direct evolution 3. They are helpful in evolution. eg. Low weight of starving beetles. eg. Colour of eyes and hair 105 [Class-X – Science] SPECIATION Micro Evolution : It is the evolution which is on a small scale. e.g. change in body colour of beetles. The process by which new species develop from the existing species is known as speciation. Speciation : it is the process of formation of new species. Species : A group of similar individuals within a population that can interbreed and produce fertile offspring. Geneflow : It is exchange of genetic material by interbreeding between populations of same species or individuals WAYS BY WHICH SPECIATION TAKES PLACE Speciation takes place when variation is combined with geographical isolation. Gene flow : occurs between population that are partly but not completely separated. Sub Population X1 (local) Interbreeding [Reproduction] Gene flow Sub Population X1 (migrant) Variation in Local population GENETIC DRIFT It is the random change in the frequency of alleles (gene pair) in a population over successive generations. *Natural Selection : The process by which nature selects and consolidate those organisms which are more suitably adapted and possesses favorable variations [Class-X – Science] 106 POPULATION Z Sub Population Z1 GEOGRAPHICAL BARRIER ISOLATION (River, Mountain) Sub Population Z2 Over many-many generations Results in Accumulation of different variations in Sub population Z1 and Z2 Genetic drift Natural selection Sub population Z1 and Z2 incapable of interbreeding Reproductive Barrier Formation of Formation of new Species 1 new Species 2 Genetic drift takes place due to : (a) Severe changes in the DNA (b) Change in number of chromosomes Evolution and Classification Both evolution and classification are interlinked. 1. Classification of species is reflection of their evolutionary relationship. 2. The more characteristic two species have in common the more closely they are related. 107 [Class-X – Science] 3. The more closely they are related, the more recently they have a common ancestor. 4. Similarities among organisms allow us to group them together and to study their characteristic. TRACING EVOLUTIONARY RELATIONSHIPS (Evidences of Evolution) I. Homologous Organs : (Morphological and anatomical evidences. These are the organs that have same basic structural plan and origin but different functions. Homologous organs provides evidence for evolution by telling us that they are derived from the same ancestor. [Class-X – Science] 108 Example : Forelimb of Horse Winds of bat Paw of a cat II. (Running) (flying) (walk/scratch/attack) Same basic structural plan, but different functions perform. Analogous Organs : These are the organs that have different origin and structural plan but same function example : Example : Analogous organs provide mechanism for evolution. Wings of bat elongated fingers with skin folds Wings of bird Feathery covering along the arm Different basic structure, but perform similar function i.e., flight. III. Fossils : (Paleontological evidences) The remains and relics of dead organisms of the past. FOSSILS ARE PRESERVED TRACES OF LIVING ORGANISMS Fossil Archaeopteryx possess features of reptiles as well as birds. This suggests that birds have evolved from reptiles. Examples of Fossils AMMONITE - Fossil-invertebrate TRILOBITE - Fossil-invertebrate KNIGHTIA - Fossil-fish RAJASAURUS - Fossil dinosaur skull AGE OF THE FOSSILS 1. ........................... I. Deeper the fossil, older it is. 2. ........................... Recent II. Detecting the ratios of difference 3. ........................... of the same element in the fossil 4. ........................... material i.e. Radio-carbon dating 5. .......................... [C-(14) dating) 6. .......................... Older 109 [Class-X – Science] Evolution by Stages Evolution takes place in stages ie bit by bit over generations. I. Fitness Advantage Evolution of Eyes : Evolution of complex organs is not sudden it occurs due to minor changes in DNA, however takes place bit by bit over generations. enough to Flat worm has rudimentary eyes give fitness advantage Insects have compound eyes Humans have binocular eyes II. Functional Advantage Evolutions of Feathers Feathers provide insulation in cold weather but later they might become useful for flight. Example : Dinosaurs had feathers, but could not fly using feathers. Birds seem to have later adapted the feathers to flight. WILD CABBAGE KALE CABBAGE with larger leaves with short distance between the leaves BROCCOLI KOHL RABI CAULIFLOWER Arrested flower development Has sterile flowers Evolution by Artificial Selection [Class-X – Science] 110 With Swollen parts Evolution by Artificial Selection : Humans have been a powerful agent in modifying wild species to suit their own requirement through out ages by using artificial selection. e.g. (i) From wild cabbage many varieties like broccoli, cauliflower, red cabbage, kale, cabbage and kohlrabi were obtained by artificial selection. (ii) Wheat (many varieties obtained due to artificial selection). Molecular Phylogeny It is based on the idea that changes in DNA during reproduction are the basic events in evolution Organisms which are more distantly related will accumulate greater differences in their DNA HUMAN EVOLUTION Tools to Study Human Evolutionary Relationship Excavating Time dating Fossils Determining DNA Sequences Although there is great diversity of human forms all over the world get all humans are a single species GENETIC FOOTPRINTS OF HUMANS Hundreds/thousand of years ago Earliest members arose in Africa East Asia South Africa Africa Philippines Island of Indonesia West Asia 111 Central Asia Australia Eurasia [Class-X – Science] They did not go in a single line They went forward and backward Moved in and out of Africa Sometimes came back to mix with each other. Very Short Answers (1 Mark) 1. Define variation 2. What is monohybrid cross? 3. What are genes? 4. If an individual has XX chromosome [22 + XX] will that individual be male or female. 5. Which plant Mendel had chosen for his experiments. 6. Name the branch of science that deals with Heredity and variation. 7. Name two human traits which show variation. 8. What will you get in F1 generation when a pea plant having violet coloured flowers is crossed with white coloured flowers? Give reason. 9. Who is the father of Genetics? 10. Write the scientific name of men and garden pea. 11. Where can be the Genetic foot print of human be traced? Short Answers (2 Marks) 1. Differentiate between acquired and Inherited traits? Give example of each. 2. What are fossils? How can the age of fossils be determined. [Class-X – Science] 112 3. What is speciation? What factors lead to formation of a new species. 4. Explain the mechanism of sex determination in humans. 5. Differentiate between homologous and analogous organs by giving examples. 6. Define inheritance. What are the units of inheritance. 7. What is genetic drift? How does it contribute to the formation of new species. 8. Explain monohydrid cross by taking tall and dwarf plants. Mention the phenotypic and genotypic ratio of F1 and F2 off springs. 9. How does creation of variations in a species promote survival? 10. Why did Mendel select pea plants for conducting his experiments on inheritance? 11. Why is the father responsible for the sex of a child? 12. Why are acquired traits not passed on to their progeny? Short Answer (3 Marks) 1. Describe any three ways in which individuals with a particular trait may increase in a population. 2. Name two fossils. What do fossil tells us about the process of evolution? 3. What are the important sources which provide evidence for evolution? Explain them with example. Long Answer (5 Marks each) 1. Explain the process of artificial selection by taking the example of wild cabbage plant. 2. Explain human evolution. 3. What are dominant and recessive traits? How do mendel’s experiment show that traits may be dominent or recessive? Explain with an example. 4. How do mendel’s experiments show that traits are inherited independently? Explain with a Dihybrid cross. 113 [Class-X – Science] CHAPTER – 10 LIGHT REFLECTION & REFRACTION Light is a form of energy, which enable us to see the object. In this chapter we will study the phenomena of reflection and refraction using the property of light i.e. straight line propagation (Light wave travel from one point to another, along a straight line). Reflection of Light When the light is allowed to fall on highly polished surface, such as mirror, most of the light gets reflected. Laws of Reflection 1. The angle of incidence is always equal to angle of reflection. i = r normal Reflected ray Incident ray i r Point of incidence 2. The incident ray, reflected ray and the normal to the reflecting surface at the point of incidence lie in the same plane. [Class-X – Science] 114 Image formed by Plane Mirror (Plane reflecting surface) Plane Mirror 1 A A Object B Image i r B1 1. Virtual (imaginary) & Erect ( The image that do not form on screen.) 2. Laterally inverted (The left side of object appear on right side of image) 3. The size of image is equal to that of object. 4. The image formed is as far behind the mirror as the object is in front of it. Reflection of light by spherical Mirrors Mirrors, whose reflecting surface are curved inward or outward spherically are called spherical mirror. For example - Spoon } The curved surface of shinning spoon can be considered as curved mirror. Reflecting side Reflecting side Concave Mirror OR CONVERGING MIRROR Convex mirror OR DIVERGING MIRROR 115 [Class-X – Science] If it is curved inward Act as concave mirror If it is curved outward Act as a convex mirror.. Few Basic terms related to Spherical Mirror Principal Axis Radius of curvature R F f focal length C Concave Mirror P Radius of curvature R Principal Axis P f F focal length Convex Mirror C 1. Principal axis : Line joining the pole and centre of curvature of the spherical mirror. 2. Pole : The geometrical central point of the reflecting spherical surface. (aperture), denoted by (P). 3. Aperture : The width of reflecting spherical surface. 4. Centre of curvature : The centre of the hollow glass sphere of which the spherical mirror is a part is called as centre of curvature. 5. Radius of curvature : The distance between the pole and the centre of curvature. i.e. PC = R or The radius of the hollow sphere of which the mirror is a part. 6. Focus point : The point on the principal axis, where all parallel rays meet after reflection is called as Principal Focus or Focus. It is denoted by letter ‘F’. [Class-X – Science] 116 7. Focal length : The distance between the pole and focus point i.e. PF = f 8. Relationship between focal length and Radius of curvature. F= R 2 Image Formation by Spherical Mirror Before we learn the formation of image or ray diagram, let us go through few tips (a) Remember, a ray of light which is parallel to principle axis always pass through focus (meet at focus) or vice-versa. P Principal Axis C P Principal C Axis F F CONCAVE MIRROR CONCAVE MIRROR Principal Axis P C F CONVEX MIRROR Appear as if coming from focus pt in case of convex mirror Principal Axis P F C (b) A ray of light which passes through centre of curvature (it is also known as normal at the point of incidence on spherical mirror) will retrace their path after reflection. 117 [Class-X – Science] Pole (P) Principal Axis F C CONCAVE MIRROR P Principal Axis F CONVEX MIRROR C (c) A ray of light falling on pole get reflected at the same angle on the other side of principal axis. P i = r F C X i = r i r C F Note : A ray of light passes through centre of curvature of reflecting spherical surface always act as normal at the point of incidence. If we know the normal we can draw angle of incidence and angle of reflection i r g (passin c) gh u o r th [Class-X – Science] C al norm ence c in f id at pt o 118 F P r i P F C Note 1 : The image will only form when two or more rays meets at a point. Image formation by a concave mirror for different position of the object. The ray diagrams given in NCERT Books are also good to be followed. Image Formation by Concave Mirror Position of Object Position of Image Nature of Imag Size of Image 1. At infinity At focus Real and invered Highly diminished (point size) 2. Beyond C Between F & C Real and invered Small 3. At CAt C Real and inverted Same size of object 4. Between C & F Beyond C Real and inverted Enlarged 5. At F At infinity Real and inverted Highly Enlarged Behind the mirror Virtual and errect Enlarged 6. Between F & P 1. Object At infinity Position of Image At focus P C 2. Object Beyond C F Size of Image Highly diminished (point size) A object B B1 P F C Nature Real and Inverted Position of Image Between F&C Nature Real and Inverted Size of Image Small A1 119 [Class-X – Science] 3. Object At C Position of Image At C A B1 B P F Size of Image Same Size of object A Object 4. Between C&F i = r Position of Image P Beyond C A Object B1 i r B C F Image A 5. Nature Real and Inverted Nature Real and Inverted Size of Image Enlarged 1 Object At F A B C F i r P i = r Position of Image At (infinity) Nature Real and Inverted Size of Image Highly enlarged A1 6. Object Between F&P (Special Case) A C F i B r P B1 Position of Image Behind the mirror Size of Image Enlarged [Class-X – Science] 120 Nature Virtual and Erect Image Formation by Convex Mirror 1. Object At infinity P F Position of Image At focus 2. Size of Image Highly diminished C Nature Virtual & erect Object Anywhere between infinity and pole A of the mirror 1 A P B Position of Image Between P & F B1 Size of Image Very small F Nature Virtual & erect Uses of Concave Mirror 1. Used in torches, search light and headlight of vehicle. 2. Used to see large image of face as shaving mirror 3. Used by dentist to see large images of the teeth 4. Large concave mirror used to focus sunlight (heat) in solar furnaces. Uses of Convex Mirror 1. Used as rear-view mirror in vehicles because it gives erect image. It also helps the driver to view large area. Sign Convention for Reflection by Spherical Mirror 1. The object is always placed to the left side of mirror. 121 [Class-X – Science] 2. All distance should be measured from pole (P); parallel to principalaxis. 3. Take 'P' as origin. Distances measured Right of the origin (+x-Axis) are taken positive Left of the origin (–x-Axis) are taken negative Perpendicular to and above principal axis (+y-Axis) are taken positive Perpendicular to and below principal axis (–y-Axis) are taken negative +y o –x (Cartesian system) +x –y Mirror Formula 1 1 1 = + f v u R where f = 2 fdistance between F and Pole vdistance of image from Pole u distance of object from Pole Rdistance between centre of curvature and pole. Magnification It is expressed as the ratio of the height of the image to height of theobject. height of image h1 m= = height of object h 1 It is also related to 'u' and 'v' –v m= u 2 from 1 and 2 equation m= 1 h1 – v where h image height from principle axis h1 Object height from principle axis. h = u [Class-X – Science] 122 If magnification m > 1 _____ Image is magnified m = 1 _____ Image is of same size m < 1 _____ Image is diminished. Few tips to remember sign convention for Spherical mirror Mirror : f u v Concave : –ve –ve –ve (Real), +ve (virtual) Convex : +ve, +ve, –ve h – is always +ve h´ – is +ve for virtual –ve for Real. Refraction of Light Refraction of Light : Happens in Transparent medium when a light travels from one medium to another, refraction takes place. A ray of light bends as it moves from one medium to another Refraction is due to change in the speed of light as it enters from one transparent medium to another. Speed of light decreases as the beam of light travel from rarer medium to the denser medium. normal normal Incident Ray Rarer medium Denser medium Denser medium Rarer medium Refracted Ray When ray travel from Rarer to Denser it bends When ray travel from denser towards normal after refraction to rarer medium it bends away from normal 123 [Class-X – Science] Some Commonly observed phenomenon due to Refraction 1. The stone at the bottom of water tub appears to be raised. 2. A fish kept in aquarium appears to be bigger than its actual size. 3. A pencil partially immersed in water appears to be displaced at the interface of air and water. Refraction through a Rectangular Glass Slab Here light ray changes is direction at O and O1 , the point at the interface of transparent medium. When a incident ray of light AO passes from a rarer medium (air) to a denser medium (glass) at point. O on interface KL, it will bends towards the normal. At pt O1, on interface NM the light ray entered from denser medium (glass) to rarer medium (air) here the light ray will bend away from normal OO1 is a refracted ray O1B is an emergent ray. If the incident ray is extended to C, we will observe that emergent ray O1B is parallel to incident ray. The ray will slightly displaced laterally after refraction. Note : When a ray of light is incident normally to the interface of two media it will go straight, without any deviation. Laws of Refraction of Light 1. The incident ray, the refracted ray and the normal to the interface of [Class-X – Science] 124 two transparent media at the point of incidence, all lie in the same plane. 2. The ratio of sine of angle of incidence to the sine of angle of refraction is a constant i.e. Sin i constant Sin r = (r) for given colour and pair of media, this law is also known as Snell’s Law Constant n is the refractive index for a given pair of medium. It is the refractive index of the second medium with respect to first medium. n2 Sin i Sin r = n1 = n21 Where 2 is for second medium and 1 is for first medium Refractive Index The refractive index of glass with respect to air is given by ratio of speed of light in air to the speed of light in glass. nga = Speed of light in air c = v Speed of light in glass C Speed of light in vacuum = 3×108 m/s speed of light in air is marginally less, compared to that in vacuum. Refractive index of air with respect to glass is given by a air g glass nag = Speed of light in glass v = c Speed of light in air The absolute refractive index of a medium is simply called refractiveindex. Speed of light in air c nm = = v Speed of light in the medium Refractive index of water (nw) = 1.33 Refractive index of glass (ng) = 1.52 125 [Class-X – Science] Spherical Lens A transparent material bound by two surfaces, of which one or both surfaces are spherical, forms a lens. Convex lens Concave lens 1. Bulging outwards 1. Bulging inwards. 2. Converging lens. 2. Diverging lens. Convex Lens A lens may have two spherical surfaces, bulging outwards, is called double convex lens (or simply convex lens). It is also known as converging lens because it converges the light. Concave Lens A lens bounded by two spherical surfaces, curved inwards is known as double concave lens (or simply concave lens) It is also known as diverging lens because it diverges the light. [Class-X – Science] 126 Few Basic Terms Related to Spherical Lens R Principal Axis C1 or (2F1) f O F1 F2 Optical centre (O) R Principal Axis C1 C2 or (2F2) Optical centre (O) O F1 F2 C2 Convex Lens Concave Lens f C1 O C2 1. Centre of curvature : A lens, either a convex lens or a concave lens is a combination of two spherical surfaces. Each of these surfaces form a part of sphere. The centre of these two spheres are called centre of curvature represented by C1 and C2. 2. Principal axis : Imaginary straight line passing through the two centres of curvature 3. Optical Centre : The central point of lens is its optical centre (O). A ray of light, when passes through 'O' it remains undeviated i.e. it goes straight. 4. Aperture : The effective diameter of the circular outline of a spherical lens. 5. Focus of lens : Beam of light parallel to principal axis, after refraction from 127 [Class-X – Science] 1. Convex lens, converge to the point on principal axis, denoted by F, known as Principal focus Principal Axis F1 2. O F2 Concave lens, appear to diverge from a point on the principal axis known as principal focus. O F1 F2 Principal Axis The distance OF2 and OF1 is called as focal length Tips for Drawing Ray Diagram (a) After refraction, a ray parallel to principal axis will pass through F. (b) A ray passes through F, after refraction will emerge parallel to principal axis. (c) A ray passes through optical centre 'O', passes without any deviation. [Class-X – Science] 128 Image formation by a convex lens for various position of object 1. Object At infinity 2F1 2. F1 F2 2F2 Object Beyond 2F1 Position of Image At focus F2 Size of Image Highly diminished (point size) Nature Real & inverted Position of Image Between F2 & 2F2 Nature Real & inverted Size of Image Small 3. Object At 2F1 A 1 B B 2F1 F1 2F2 F2 A1 4. Object Between F& 2F 1 1 Position of Image At 2F2 Size of Image Same size of object Position of Image Beyond 2F2 Size of Image Enlarged 129 Nature Real & inverted Nature Real & inverted [Class-X – Science] 5. Object At focus F1 Position of Image at infinity Size of Image Highly Enlarged 6. (Special Case) Object Between F1 and optical centre 'O' Nature Real & inverted Size of Image Enlarged Nature Virtual & Erect Position of Image At F1 Nature Virtual & Erect Position of Image On the same side of the object Image Formation by Concave Lens 1. Object At infinity Size of Image Highly Diminished 2F1 2. F1 F2 O 2F2 Object Between infinity and optical centre (at any point) Position of Image Between F1 & O Size of Image Very small A A B 2F1 [Class-X – Science] F1 B F2 O 130 2F2 Nature Virtual & Erect Sign Convention for Refraction by Spherical Lens Similar to that of spherical mirror, only the difference is that all the measurement are made from optical centre 'O' + y-axis o + x-axis – x-axis – y-axis Lens Formula 1 1 – 1 = f v u 'O' optical centre f - distance between F and 'O' u - distance of object from 'O' R 2 v - distance of image from 'O' R - distance between centre of curvature & 'O' f= Magnification It is defined as the ratio of the height of image to the height of object. m= height of image height of object 1 = h = 1 h h1 – image height from principal axis h – object height from principal axis It is also related to 'u' & 'v' m= v u 2 From equation 1 & 2 m= h1 h = v u If magnification m > | Image is magnified m = 1 Image is of same size m < | Image is diminished 131 [Class-X – Science] Few Tips to Remember Sign Convention for Spherical Lens Lens : f–u–v Concave : –ve –ve –ve (Virtual) Convex : +ve, –ve +ve (Real) –ve (Virtual) h – is always +ve h´ – –ve for Real and +ve for Virtual & Errect. Power of Lens The degree of convergence or divergence of light ray achieved by a lens is known as power of a lens. It is defined as the reciprocal of its focal length Represented by P. If f is given in meter, then 1 P= f If f is given in cm, then 100 P= f SI unit of power of a lens is "dioptre" denoted by 'D' I d io p tre o r ID It is the power of lens whose focal length is 1m 1 1D = OR 1D = 1m–1 1m f is +ve [Class-X – Science] 132 Power of concave lens or diverging lens is always negative f is –ve If any optical instrument has many lens, then net power will be P = P1 + P2 + P3.... Very Short Answers Type Questions (1 Mark) 1. If the angle of incidence is 0°, what is the angle of reflection? 2. What is the nature of image formed by concave mirror if the magnification produced by the mirror is +3? 3. Give two uses of concave mirror? 4. Find the focal length of a convex mirror, whose radius of curvature is 30 cm? 5. What do you understand by magnification of a spherical mirror? 6. An object is held at the principal focus of a concave lens of focal length f. Where the image will form? 7. Show the angle of incidence and angle of reflection. F 8. Complete the ray diagram. 133 [Class-X – Science] 9. Define the SI unit of power of lens. 10. When light undergoes refraction at the surface of separation of two media, what happens to speed of light. 11. How can we find the focal length of a Convex lens quickly but approximately. Short Answer Type Questions (2-3 Marks) 1. What do you understand by refraction of light. Draw the labelled ray diagram, when ray of light passes through glass slab. 2. The refractive index of glass is 1.54 and the speed of light in air is 3 × 108 m/s. Calculate the speed of light in glass. 3. A convex mirror used in an automobile has a focal length of 6m. If vehicle behind is at a distance of 12m. Find the nature and location of image. (4m, virtual erect small) 4. A concave lens of focal length 15cm, forms an image 10 cm from the lens. How far is the object placed from the lens? Draw the ray diagram? 5. Two thin lens of power +3.5D and - 2.5D are placed in contact. Find the power and focal length, if the lens are in combination.(p = + 1D, f = 1m) 6. What are the laws of refraction. Define refractive index of a medium. 7. How we can differentiate between convex and concave lens without touching it. 8. The Power of a combination of two lens XY is 5D if the focal length of lens X is 15 cm. State the Nature & focal length of lens Y. (–60 cm. Concave lens.) Very Long Answer Type Questions (5 Marks) 1. Draw the ray diagram, showing the image formed by concave mirror, when object is placed at (a) at infinity (b) between F and 2F (c) At 2F (d) At F [Class-X – Science] 134 (e) between F&P 2. Draw the ray diagram, showing the image formed by convex lens, when object is placed at. (a) At infinity (b) between F1 & 2F1 (c) At 2F1 (d) Beyond 2F1 (e) between F1 & optical centre 'O' 135 [Class-X – Science] CHAPTER – 11 THE HUMAN EYE AND THE COLOURFUL WORLD In this chapter we will study Human eye that uses the light and enable us to see the objects. We will also use the idea of refraction of light in some optical phenomena in nature i.e. Rainbow formation, twinkling of star, blue and red colour of sky etc. Human Eye : A Sensitive sense organ It acts like a camera, enable us to capture the colourful picture of the surroundings. It forms an inverted, real image on light sensitive surface Retina The Various Parts of Eye and their Functions 1. Cornea : It is a thin membrane through which light enters. It forms the transparent bulge on the front of eyeball. Most of the refraction occurs at the outer surface of the cornea. [Class-X – Science] 136 2. Eyeball : it is approximately spherical in shape, with a diameter of about 2.3cm. 3. Iris : It is a dark muscular diaphragm that controls the size of pupil. It is behind the cornea. 4. Pupil : It regulates and control the amount of light entering the eye. It is the black opening between aqueous humour & lens. 5. Crystalline eye lens : Provides the focussed real & inverted image of the object on the retina. It is composed of a fibrous, jelly like material. This is convex lens that converges light at retina. 6. Ciliary muscles : It helps to change the curvature of eyelens and hence changes its focal length so that we can see the object clearly placed at different positions. 7. Retina : Thin membrane with large no. of light sensitive cells. 8. When image is formed at retina, light sensitive cells gets activated and generate electrical signal. These signals are sent to brain via optic nerve. Brain analyse these signals after which we perceive object as they are. How Pupil Works? Example : You would have observed that when you come out of the cinema hall after watching movie, in the bright sun light, your eyes get closed . And when you enter the hall from the bright light, you won't be able to see but after some time you would be able to see. Here the pupil of an eye provides a variable aperture, whose size is controlled by iris (a) When the light is bright : Iris contracts the pupil, so that less light enters the eye. (b) When the light is dim : Iris expand the pupil, so that more light enters the eye. Pupil opens completely, when iris is relaxed. 137 [Class-X – Science] Persistence of Vision : It is the time for which the sensation of an object continue in the eye. It is about 1/16th of a second. Power of Accommodation The ability of eye lens to adjust its focal length with the help of ciliary muscles is called accommodation. Ciliary Muslces Relaxed Contract 1. Eye lens becomes thick 2. Decreases the focal length 3. Enable us to see nearby object clearly Near point of the Eye It is 25cm for normal eye. The minimum distance at which object can be seen most distinctly without strain. For point of the Eye It is infinity for normal eye. It is the farthest point upto which the eye can see objects clearly. Defects of Vision and their Correction 1. Cataract : The image can not be seen distinctly because eye lens become milky and cloudy. This condition is known as cataract, it can cause complete or partial loss of vision. This can be corrected by surgical removal of extra growth (cataract surgery). 2. Myopia : (Near Sightedness) A person can see nearby object clearly, but cannot see distant object distinctly. [Class-X – Science] 138 Image formed in front of the retina. Normal Eye O1 O Image formed at Retina Object Myopic Eye O The Reason of defect 1. Excessive curvature of eye lens means Eye lens becomes thick and its focal length decreases. 2. Elongation of the eye ball. Correction Corrected by using a Concave Lens of appropriate power. O1 O Correction of Myopita 3. Hypermetropia (Far - Sightedness) A person cannot see nearby object clearly, but can see distant object distinctly. 139 [Class-X – Science] Image formed at a point behind the retina NORMAL EYE N Image formed at Retina Hypermetropic eye N1 N The Reason of defect 1. Increase in focal length of the eye lens (Thin eye lens) 2. Eye ball has become too small. Correction Corrected by using a Convex Lens of appropriate power.. N N1 Correction of Hypermetropic eye 4. Presbyopia As we become old, the power of accommodation of the eye usually decreases, the near point gradually recedes away. This defect is called Presbyopia, a special kind of Hypermetropia. [Class-X – Science] 140 Person may suffer from both myopia and hypermetropia. Reason of defect : Gradual weakening of ciliary muscles and decreasing the flexibility of the eye lens. Correction : Using Bifocal lens with appropriate power. Bifocal lens consist of both concave and convex lens, upper position consist of concave lens and lower portion consist of convex lens. Refraction of Light through a Prism Prism : It has two triangular bases and three rectangular lateral surfaces. These surfaces are inclined to each other. The angle between its two lateral faces is called Angle of Prism. A Angle of Prism (Angle of deviation) D i- incident angle i t ligh Sun r B e (emergent angle) Em erg ent C ray Angle of Deviation (D) The angle between the incident ray and emergent ray. Dispersion of white light by a Glass Prism D for red colour D for violet colour ht te lig Whi beam R While light Spectrum D for violet colour > D for red colour 141 V [Class-X – Science] Inclined refracting surfaces of glass prism show exciting phenomenon. Splitting of White Light into Band of Colours The band of the coloured components of light beam is called Spectrum i.e. VIBGYOR The splitting of light into its component colours is called Dispersion. The different component colour of light bends at different angle with respect to incident angle, the red light bends the least while the violet bends most. ISSAC NEWTON He was the first, who obtained spectrum of sunlight by using glass prism. He tried to split the spectrum of white light more by using another similar prism, but he could not get any more colours. He repeated the experiment using second prism in an inverted position with respect to the first prism. Allowed all the colours of spectrum to pass through second prism. He found white light emerges on the other side of second prism. en Scre e li whit ght R R V V e whit h lig t rce Sou He concluded that sun is made up of seven visible colour ‘VIBGYOR’ RAINBOW It is the spectrum of sunlight in nature It is formed due to the dispersion of sunlight by the tiny water droplet, present in atmosphere. Water Droplet Act like Prism It refracts and disperses the incident sunlight, then reflects it internally (internal reflection) and finally refracts it again, when it emerges out of the water droplet. [Class-X – Science] 142 A rainbow is always formed in a direction opposite to that of sun. Due to dispersion and internal reflection of light, different colours reach the observer’s eye. Red colour appears on top & violet at the bottom of rainbow Sunlight Rain drop A At ‘A’ Refraction & dispersion takes place B At ‘B’ Internal refraction takes place C At ‘C’ Refraction & dispersion takes place R V Atmospheric Refraction 1. Apparent Star Position : It is due to atmospheric refraction of starlight. The temperature and density of different layers of atmosphere keeps varying. Hence we have different medium. Distant star act as point source of light. When the starlight enter the earth’s atmosphere it undergoes refraction continuously, due to changing refractive index i.e. from Rarer to denser, it bends towards the normal. Due to this the apparent position of the star is different from actual position. The star appears higher than its actual position. Actual position of Star Apparent position of star In atmospheric layers, Refractive index decreases Atmosphere 143 [Class-X – Science] 2. Twinkling of Star : It is also due to atmospheric refraction. Distant star act like a point source of light. As the beam of starlight keeps deviating from its path, the apparent position of star keeps on changing because physical condition of earth’s atmosphere is not stationary Hence the amount of light enters our eyes fluctuate some time bright and some time faint. This is the “Twinkling effect of star”. Q. Ans. Why Planets do not twinkle? Planets are closer to earth and are seen as extended source of light i.e. the collection of large no. of point sized sources of light. Therefore, the total amount of light entering our eyes from all individual point source will nullify the twinkling effect. 3. Advance Sunrise and delayed sunset : This is also due to atmospheric refraction. Because of this sun is visible about 2 minutes earlier than actual sunrise and about 2 minutes after the actual sun set. Apparent position of sun Ob se Ea rve rt h r o n Atmosphere Horizon EARTH Actual Sun Apparent flattering of the sun’s disc at sun set and sun rise is due to atmospheric refraction. [Class-X – Science] 144 Scattering of Light Tyndall Effect : When a beam of light strikes the minute particle of earth’s atmosphere, i.e., suspended particles of dust and molecule of air, the path of beam becomes visible. The phenomenon of scattering of light by the colloidal particle gives rise to Tyndall Effect. It can be observed when sunlight passes through a canopy of a dense forest. The colour of the scattered light depends on the size of the scattering particles. Very fine particle (scatter mainly blue colour short wave length) Large size particle (Scatter light of longer wave length i.e. red) Very large enough (The sky appear white) 1. Why cloud Appear white : The size of water droplet (scattering particle) is very large, hence scattered all wavelength of light almost equally. 2. Why colour of sky is blue : The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light. Since the blue has shorter wavelength than red, hence it will be scattered the most. According to Rayleigh scattering 1 Scattering of light 4 – Wavelength) Scattering of light decreases with increase in wavelength Q. Ans. If there is no earth’s atmosphere? What will happen to scattering phenomenon? There will be no scattering and sky will appear dark. 3. Colour of the Sun at Sunrise and Sunset. While sunset and sunrise, the colour of the sun and its surrounding appear red. 145 [Class-X – Science] During sunset and sunrise, the sun is near horizon, and therefore the sunlight has to travel larger distance in atmosphere. Due to this most of the blue light (shorter wavelength) are scattered away by the particles. The light of longer wavelength (red colour) will reach our eye. This is why sun appear red in colour. 4. Why the danger signal or sign are made of red colour. Red colour scattered the least when strikes the small particle of fog and smoke because it has the maximum wavelength (visible spectrum). Hence at large distance also, we can see the red colour clearly. 5. At noon sun appear white : At noon, the sun is overhead and sunlight would travel shorter distance relatively through the atmosphere. Hence, at noon, the Sun appear white as only little of the blue and violet colours are scattered. (In the afternoon) (In the early morning or evening) Light travel less distance in atmosphere. (Less blue scattered) (Blue scattered away sun appear reddish Sun near horizon Atmosphere EARTH Very Short Answers (1 Mark) 1. What is the phenomenon responsible for the blue colour of sky? 2. What is the near and far point of a normal eye? 3. Name the component of eye that is responsible for the adjustment of eyelens? [Class-X – Science] 146 4. To an astronaut why does the sky appear dark instead of blue? 5. How can your remove the defect of vision ‘Presbyopia’. 6. Name three primary colour? (Ans. RED, BLUE, GREEN) 7. Write the nature of image formed by our eye? 8. What do you understand by Dispersion of light? 9. What is Tyndall Effect? 10. A student has difficulty in reading the black board while sitting in the last row. What is the defect of vision and how it can be corrected? 11. What is the value of Power of Accommodation of Person having normal eyesight? 12. Name the Part of the retina which is sensitive of light? Short Answers (2 Marks) 1. Name the phenomenon responsible for formation of rainbow? Explain it with the help of diagram? 2. What is power of accommodation. How ciliary muscles helps in accommodation? 3. Why the sun appear red while sunset and sunrise. Explain? 4. Why the star twinkle but not earth planets? 5. Explain the function of (i) Iris (ii) Pupil (iii) Retina 6. Explain the refraction of light through glass prism with the help of diagram. Show angle of emergence and angle of deviation? 7. Name (a) the Eye defect which can’t be corrected by any type of lens. (b) the Old Age hypermetropia. 147 [Class-X – Science] Long Answer Type Questions (5 Marks) 1. What is myopia. State the two causes of myopia? With the help of labelled ray diagram show (a) Eye defect (b) Correction of myopia 2. What is hypermetropia. State the two causes? With the help of labelled ray diagram show (a) Eye defect (b) Correction of hypermetropia. 3. Draw the labelled diagram of human eye and explain the image formation? [Class-X – Science] 148 CHAPTER – 12 ELECTRICITY Think life without “electricity” in this modern society. Is it possible to survive without electrical energy in world of technology. Since we are science student, so it is necessary to understand the basic concept behind the word “electricity”. Charge (q) It is a very small particle present in an atom. It can be either negative (electron) or positive (proton) “Coulomb” is the SI unit of charge, represented by C. Net charge (Q) – Total charge IC Net charge is equivalent to the charge contained in nearly electrons 6 × 1018 electron. Q = ne (n is no. of electrons) –19 If Q = 1C, e = 1.6 × 10 C (negative charge on electron) Q 1 n= e = –19 1.6 ×10 100 18 18 = × 10 = 6.2 × 10 16 18 n = 6 × 10 electron Current (I) Rate of flow of net charge is called current. Denoted by (I) I = Q t t is time 149 [Class-X – Science] SI unit of current is “Ampere” rep. by A. Ampere Defined as one coulomb of charge flowing per second. 1C 1s 1A = In an electric circuit the electric current flow in an opposite direction to the flow of electron (–ve charge) conventionally. It flows from the +ve terminal of battery or cell to –ve terminal. Small quantity of current are expressed in mA (milli Ampere) = 10–3 A µA (micro Ampere) = 10–6 A Ammeter : It is an instrument used to measure the electric current in a circuit. It is always connected in series in a circuit It is represented by the symbol –––––––– – A + ––––––– in an electric circuit. It has low resistance. Electric Circuit : It is a closed path along which the electric currentflows. Bulb The arrow shows the direction of electric current in circuit. – Ammeter A + + – Key In this circuit ammeter is connected in series. Battery (Having 3 cells) The electrons can only flow when there is difference of electric potential. For example “water flowing through a tube”. It is only possible when there is high pressure at one side and low at another side, then it will move from high pressure to low pressure. [Class-X – Science] 150 In case of electric current, the flow of charge is made possible due to chemical action with in a cell that generates the potential difference across the terminals of the cell. Electric potential Difference : It is defined as the work done in carrying a unit charge from one point to another between the two points of an electric circuit. V= W Q V – Potential Difference W – Work Q – Net Charge SI unit of potential difference – Volts rep. by “V” One Volt When 1 Joule of work is done in carrying one coulomb (1C) of charge from one point to another of a current carrying conductor then the potential difference is said to be IV. IV = 1J 1C Voltmeter It is an instrument, used to measure the potential difference +V – and represented by the symbol in an electric circuit. It is always connected in parallel across the points between which the potential difference is to be measured. It has high resistance. Symbols for some commonly used instrument in circuit diagrams + (1) Cell (2) Battery – + (3) Key (switch) open – OR 151 [Class-X – Science] (4) Key (Closed) OR (5) Joint wire (6) Wires with no join (7) Bulb (8) Ammeter + (9) Voltmeter + – A – V (10) Resistance (11) Rheostat (variable Resistance) OR George Simon Ohm (Physicist) 1787 – 1854 Found the relationship between the current (I) flowing through a conductor and potential difference (V) across the terminals of a conductor using the circuit diagram. + V– GRAPH – A + V (V) + [Class-X – Science] O – 152 V I I (A) Ohm’s Law He stated that the electric current flowing through a conductor is directly proportional to the potential difference across its ends, provided the temperature remain constant VI V = IR Where “R” is the proportionality constant for the given metal at given temperature and is said to be resistance, the graph between V and I is always straight line. Resistance : It is the property of a conductor that opposes the flow of current. It is represented by ‘R’ and symbol is SI unit of resistance is “Ohm” OR 1 Ohm : The resistance of a conductor is said to be one Ohm, when the potential difference across the conductor is 1V and the current flowing through it is 1A. V = IR R= V I 1 Ohm or 1 = 1V 1A Rheostat As we know that V = IR 1=V R Shows that current through conductor/resistor is inversely proportional to its resistance So to increase or decrease the current accordingly in the circuit a component used is called “Rheostat”, that regulates the current without changing potential difference. Represented by “Rh”. Its symbol is OR 153 [Class-X – Science] If a conductor has less Resistance, then more current will flow through it. Factors on Which Resistance of a Conductor Depends 1. On its length (l) 2. On its cross sectional area (A) 3. On the nature of material. (Resistance) Rl R 1 A R l A R= l A (Directly prop. to length) (inversely prop to cross-sectional area) Where “ ” (rho) is a proportionality constant known as resistivity of the material of conductor. Resistivity ( ) : The resistance offered by a wire of unit length and unit cross-sectional area is called resistivity. Since R = Its SI unit is m l A R.A = l m2 m SI unit of m. For a material irrespective of length and area, the resistivity is a constant. Resistivity of a Material varies with Temperature Resistivity of an alloy (homogeneous mixture of metals) is generally higher than of its constituent metals. Example: Constantan (alloy of Cu & Ni) Alloys have high resistivity and do not oxidise (burn) readly at high temperature, for this reason they are commonly used in electrical heating devices, like electric iron, heater, toasters etc. For example “Tungsten” as filament of electric bulb. [Class-X – Science] 154 Resistance in Series (Maximum Effective Resistance) Let us take three conductors/resistors of resistance R1, R2 and R3 that are connected in series in a circuit. R1 R2 R3 V1 V2 V3 I + – V Ohm’s law stated V = IR The current (I) flowing through the resistance in series will remain same, where as the potential difference (V) across each resistor will be different. V = IR V1 = IR1 , V2 = IR2 , V3 = IR3 Total potential difference (V) = V1 + V2 + V3 V = IR1 + IR2 + IR3 Putting the value of V, V1, V2 & V3 I R = I (R1 + R2 + R3 ) Reff = R1 + R2 + R3 Thus, we conclude that effective Resistance of the several resistors joined in series is equal to the algebraic sum of their individual resistances. Resistance in Parallel (Minimum Effective Resistance) Let us take three resistors of resistance R1, R2 and R3, that are connected in parallel in the electric circuit. R1 I1 I2 I1 R2 I3 R3 + – V 155 [Class-X – Science] Now, I1 = V , I2 = V , I3 = V R1 R2 R3 Total current (I) = I1 + I2 + I3 substitute the value of I1, I2, I3 and I V = V + V + V R R1 R2 R3 V = V R 1 + 1 + 1 R1 R2 R3 1 = 1 + 1 + 1 Reff R1 R2 R3 Thus, we conclude that the reciprocal of total effective resistance of the several resistors connected in parallel is equal to the sum of the reciprocals of the individual resistances. Disadvantage of Series Connection in an Electric Circuit 1. In series connection if any of the component fail to work, the circuit will break and then none of the component (ex. TV, bulb, fan..) will work. 2. It is not possible to connect a bulb and a heater in series, because they need different value of current to operate properly. Hence, to overcome this problem we generally use parallel circuit. Heating Effect of Electric Current Explanation Battery or a cell is a source of electrical energy. (1) Battery or Cell (Chemical reaction in it will produce potential difference at its two terminals) [Class-X – Science] (2) Electron will come in motion to flow current through resistor 156 (5) Rest of energy of source is converted into heat, that raises the temperature of gadget. (4) Part of this energy is consumed in useful work (like rotating of fan) (6) This is known as heating effect of electric current (7) This effect is utilized in devices such as electric heater, iron etc. (3) To maintain this current, the source has to keep expending its energy Mathematical Expression Let us suppose that current (I) is flowing through a resistor of resistance (R) for the time (t). The potential difference across the resistance is (V). W V= Q Work done in moving the charge Q will be W = VQ W Then power, P = t [Rate of change of work done] VQ = t Q P = VI I= t – (1) Heat energy supplied by the source for time t will be Energy or Work (H = P t) P= – (2) time Put equation (i) in equation (2) H = VIt = (IR) It V = IR Ohm’s Law] H = I2Rt This is known as Joule’s Law The law stated that the heat produced in a resistor is : (i) directly proportional to square of the current (I) (ii) directly proportional to resistance (R) for given current 157 [Class-X – Science] (iii) directly proportional to time (t) for which current flow through resistor. Application of Heating Effect of Electric Current 1. Used in electric iron, toaster, oven, heater etc. 2. It is also used in bulb to produce light. (Filament of bulb is made of strong metal with high melting point such as tungsten (m.pt = 3380°C). This filament can retain as much of the heat generated as possible, to become very hot and emit light) 3. It is also used in the “fuse connected in an electric circuit. Fuse is a safety device, that protect the circuits and appliance by stopping the flow of high current. The wire of fuse is made of an alloy of metals e.g., Aluminium Copper, Iron, Lead etc. The alloy should be of low melting point and high resistivity, fuse is always connected in series circuit. When large current flows through the circuit, the temperature of fuse wire will increase. This melts the fuse wire and breaks thecircuit. “ Fuses” used for domestic purposes are rated as 1A, 2A, 3A, 5A, 10A etc. for various operation depending upon the power of appliance using. Example : let us consider an appliance “electric Iron” which consume 1KW electric power, at 220V P = VI I = P = 1KW = 1000W V 220V 220V I = 4.54A In this case a 5A fuse is required. Electric Power : In case of electricity, it is defined as the rate of change of electrical energy dissipated or consumed in an electric circuit. P = VI 2 or P = I R 2 V or P = R [Class-X – Science] ( V = IR Ohm’s Law) ( I= V ) R 158 or P = Electrical Energy (E) time (t) SI unit of electric power is “Watt” (W). 1 Watt Defined as the power consumed by a device, when 1A of current passes through it at the potential difference of 1V. P = VI 1 Watt = 1 Volt × 1 Ampere Electrical Energy P= E t E – Electrical Energy t – time E = P t SI unit of electrical energy = Ws or J Commercial unit of electrical energy = KWh or One unit E=P×t KWh = 1KW × h = 1000W × 3600 s 5 = 36 × 10 Ws 6 = 3.6 × 10 J (SI unit Ws = J) 6 KWh = 3.6 × 10 J One horse power = 746W Very Short Answers (1 Mark) 1. Define the SI unit of (one mark each) (a) Current 159 [Class-X – Science] (b) Potential Difference (c) Resistance (d) Electric Power (e) Electric Energy (Commercial) 2. What is the conventional direction of flow of current? 3. Define the term resistivity? 4. On what factors does the resistance of a conductor depend? 5. How is the voltmeter and ammeter connected in the electric circuit. 6. Heating effect of current carrying conductor is due to – (Ans : loss of kinetic energy of electron) 7. Why the filament of bulb has high melting point? 8. How does use of a fuse wire protect electrical appliance? 9. What is the relationship between power, current and potential difference (Ans : P = VI) 10. How many joules are there in 1KWh? Short Answer Type Questions (2-3 Marks) 1. Draw a schematic diagram of a circuit consisting of a battery of six cell of 1.5V each, three resistors each of 3 in series and a plug key. 2. State Ohm’s law. Draw the graph between V&I? 3. What is joule’s Heating effect of current, derive its expression? 4. A wire of length L and resistance R is stretched so that its length is doubled and the area of cross section is halved. How will its (i) Resistance change (ii) Resistivity change. [Class-X – Science] 160 5. An electrical appliance of power 2KW works at potential difference of 220V. Does it require fuse of 5A, give reason? 6. Calculate the total effective resistance between points A and B (i) 1 1 1 1 A 1 1 B 1 (ii) 3 3 A B 3 3 (iii) 2 2 A 2 2 B 7. A Heating coil has a resistance of 200. At what Rate will heat be produced in it when a current of 2.5A flow through it? 8. Which is the better way to connect lights and other appliances in domestic wiring and why? 9. How does the resistance of a wire change when (a) its length is Tripled. (b) its diameter is doubled? 161 [Class-X – Science] Long Answer Type Questions (5 Marks) 1. On what factors does the resistance of conductor depends? Give its mathematical expression. Give the SI unit of resistivity. Calculate the resistivity of a metal of length 2m at 20°C having the resistance of 20 and diameter 0.3 mm? 2. In a circuit below: 4 2 6 + – 6V (a) Calculate total effective resistance (b) The total current through the circuit. (c) Potential difference across 4 and 2. 3. Three resistance of 2, 3 and 5 are connected in the electric circuit. Calculate the (a) Maximum effective resistance (b) Minimum effective resistance 4. Explain Joule how of heating? How and on what factor does the heat produced in a conduct depends? [Class-X – Science] 162 CHAPTER – 13 MAGNETIC EFFECTS OF ELECTRIC CURRENT In this chapter, we will study the effects of electric current : 1. Hans Christian Oersted (1777-1851) Oersted showed that electricity and magnetism are related to each other. His research later used in radio, television etc. The unit of magnetic field strength is named Oersted in his honour. 2. Oersted Experiment R K X XY is conductor (Cu wire) through which current is passed Y – + On passing the current through the copper wire XY in the circuit, the compass needle which is placed near the conductor gets deflected. If we reverse the direction of current, the compass needle deflect in reverse direction. If we stop the flow of current, the needle comes at rest. Hence, it conclude that electricity and magnetism are linked to each other. It shows that whenever the current will flow through the conductor, then magnetic field around. it will develop. 3. Magnetic Field : It is the region surrounding a magnet, in which force of magnet can be detected. It is a vector quantity, having both direction & magnitude. 163 [Class-X – Science] 4. Compass Needle : It is a small bar magnet, whose north end is pointing towards north pole and south end is pointing towards south pole of earth. 5. Magnetic Field Lines : The tangent to the magnetic field line at a point gives the direction of magnetic field at that point. N S Hence, magnetic field line is a path along which a hypothetical free north pole tend to move towards south pole. 6. Characteristics of Magnetic field lines : (a) The direction of magnetic field lines outside the magnet is always from north pole to south pole of bar magnet and are indicated by an arrow. Inside the magnet, the direction of field lines is from its south pole to north pole Thus magnetic field lines are closed curves. (b) The strength of magnetic field is expressed by the closeness of magnetic field lines. Closer the lines, more will be the strength and farther the lines, less will be the magnetic field strength. (c) No two field lines will intersect each other. If they intersects, then at point of intersection the compass needle will show two directions of magnetic field which is not possible. Tangent at the point of intersection shows two direction. [Class-X – Science] 164 7. Magnetic field due to Current Carrying Conductor N x S Cu wire + N y S x y Cu wire + – – (a) (b) The above electric circuit in which a copper wire is placed parallel to a compass needle, shows the deflection in needle gets reversed, when the direction of current reversed. Hence electricity and magnetism are related to each other. 8. Right Hand Thumb Rule It is a convenient way of finding the direction of magnetic field associated with current carrying conductor. Hold the straight wire carrying current in your right hand such that thumb points towards the direction of current, then your folded fingers around the conductor will show the direction of magnetic field. Direction of magnetic field lines. This rule is also called Maxwell’s corkscrew rule. 9. Magnetic Field due to Current through a Straight Conductor + A – Direction of Current Direction can be explained using Right Hand Thumb Rule Direction of magnetic field + – Rheostat 165 [Class-X – Science] Z S 10. Magnetic Field due to Current through a circular Loop – + Every point on the wire carrying current give rise to the magnetic field, appearing as a straight line at the centre of loop. By applying Right hand Thumb rule, we can find the direction of magnetic field at every section of the wire. 11. Solenoid : A Coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called solenoid. 12. Magnetic field due to a current in a solenoid : S N + – – Using R.H. Thumb Rule, we can draw the pattern of magnetic field lines around a current carrying ‘Solenoid’. – One end of the solenoid behaves as a magnetic north pole, while the other end behave as the South Pole. – The filed lines inside the solenoid are in form of parallel straight lines, that implies that magnetic field inside the solenoid is same at all points i.e. Field is uniform. [Class-X – Science] 166 The strength of the magnetic field produced depends upon (a) the number of turns (b) Strength of current in the solenoid used in making solenoid. 13. Electromagnet : Strong magnetic field inside the solenoid can be used to magnetise a magnetic material for example soft iron, when it is placed inside the coil. The magnet so formed is called electromagnet. It is a temporary magnet. 14. Force on a current carrying conductor in a magnetic field. Andre Marie Ampere (1775–1836) suggested that the magnet also exert an equal and opposite force on the current carrying conductor. Iron Stand Experiment + – Current Carrying Aluminium rod should lie between the two poles of magnet Horse shoe magnet We will observe that the rod will displace i.e. the rod will experience a force, when it is placed in magnetic field, in a perpendicular direction to its length. – The direction of the exerted force will be reversed if the direction of current through the conductor is reversed. – If we change the direction of field by inter changing the two poles of the magnet, again the direction of exert force will change. – Therefore the direction of exerted force depends on (a) direction of current (b) direction of magnetic field lines. 167 [Class-X – Science] 15. Left Hand Fleming Rule M other F ather (Force) Motion C hild Field T humb Current Fore finger Middle finger Thrust (force) Three of them perpendicular to each other. OR A Current Magnetic field B East For ce o rM otio n South D C Vertically downwards – According to this rule, stretch thumb , forefinger and middle finger of your left hand such that they are mutually perpendicular to each other. If fore finger represent direction of magnetic field & middle finger represent direction of current, then thumb will point in the direction of motion or force acting on the conductor. – Functioning of electric motor is based on this rule. It convert electrical energy into mechanical energy. 16. Michael Faraday : Gave the law of Electro magnetic Induction 17. Galvanometer : It is an instrument that can detect the presence of a current in a circuit. If pointer is at zero (the centre of scale) then there will be no flow of current. [Class-X – Science] 168 If the pointer deflect on either side right or left, this will show the direction of current. Represented by o G 18. Electro Magnetic Induction : Can be explained by two experiments (a) First Experiment “Self Induction” N S G G G In this experiment, when the north pole of bar magnet is brought closer to the coil or away from the coil, we see momentary deflection in the needle of galvanometer on either side of null point. First right and then left. Similarly, if we keep the magnet stationary and coil is made to move towards or away from the north pole of magnet. Again we will observe deflection in the needle of galvanometer. If both bar magnet and coil are kept stationary, there will be no deflection in galvanometer. This experiment can also be done with the south pole of magnet, we will observe the deflection in galvanometer, but it would be in opposite direction to the previous case. It concludes that motion of magnet with respect to coil or viceversa, changes the magnetic field. Due to this change in magnetic field lines, potential difference is induced in the same coil, which set up an induced current in the circuit. (b) Second Experiment : Mutual Induction Primary Coil + Secondary Coil – Coil 1 G Coil 2 169 [Class-X – Science] In this experiment plug in the key that connects coil with battery and observe the deflection in galvanometer. Now plug out the key that disconnect the coil-1 from battery and observe the deflection in galvanometer, which will be in reverse direction. Hence, we conclude that potential difference is induced in secondary coil (coil-2), whenever there is a change in current, in primary coil (coil-1) (by on and off of key). This is because, whenever there is change in current in primary coil Magnetic field associated with it also changes Now, magnetic field lines around the secondary coil (coil-2) will change and induces the electric current in it (observed by the deflection of needle of Galvanometer in secondary circuit) This process, by which changing of strength of current in primary coil, induces a current in secondary coil is called Electromagnetic Induction” The induced current is found to be highest when the direction of motion of coil is at right angles to the magnetic field. 19. Fleming’s Right Hand Rule (1) (2) M other Motion (movement of conductor) Thumb F ather Field (Magnetic) Fore finger OR [Class-X – Science] 170 (3) C hild Current (Induced) Middle finger D North Induced current Magnetic field A West Motion C Vertically downwards Rule can be defined as : Stretch thumb , forefinger and middle finger of right hand, so that they are perpendicular to each other. The forefinger indicates direction of magnetic field, thumb shows the direction of motion of conductor, then the middle finger will shows the direction of induced current. Electrical generator is based on the principle of electro magnetic induction. It convert mechanical energy into electrical energy. Current Alternate Current (AC) Direct Current (DC) (1) Changes the direction periodically after equal interval of time Does not change its direction with time, it is unidirectional Current I (A) I (A) time (s) It has frequency 50Hz in India 60 Hz in America time (s) It has frequency OHz 21. Advantages of Alternate Current (AC) over Direct Current (DC) Electric power can be transmitted to longer distances without much loss of energy. Therefore cost of transmission is low. 171 [Class-X – Science] In India the frequency of AC is 50Hz. It means after every 1/100 second it changes its direction. 22. Domestic Electric Circuits : In our homes, the electric power supplied is of potential difference V = 220V and frequency 50Hz. It consist of three wires :– (1) Wire with red insulation cover – LIVE WIRE (POSITIVE) Live wire is at high potential of 220V (2) Wire with black insulation cover – NEUTRAL WIRE (NEGATIVE) Neutral wire is at zero potential Therefore, the potential difference between the two is 220V. (3) Wire with Green insulation cover – EARTH WIRE It is connected to a copper plate deep in the earth near house. The metallic body of the appliances is connected with the earth wire as a safety measure. Function Earth wire Live wire Distribution Box containing main switch & fuse for each current Neutral wire Electrical Fuse board Electricity meter Earth wire provide a low resistance to the current hence any leakage of current to the metallic body of the appliances, keep its potential equal to that of earth. That means zero potential and the user is saved from severe electric shock. [Class-X – Science] 172 Point to be noted in Domestic Circuit (a) Each appliance has a separate switch of ON/OFF (b) In order to provide equal potential difference to each appliance, they should be connected parallel to each other. So that they can be operated at any time. (c) We have two electric circuit in our home One consist of current of 15A for high power appliances Other circuit consist of current 5A for low power appliances. 24. Short Circuiting : Due to fault in the appliances or damage in the insulation of two wires, the circuit will offer zero or negligible resistance to the flow of current. Due to low resistance, large amount of current will flow. According to Joule’s law of heating effect (HI2) heat is produced in live wire and produces spark, damaging the device and wiring. 25. Overloading : Overloading can be caused by (1) Connecting too many appliances to a single socket or (2) accidental rise in supply voltage if the total current drawn by the appliances at a particular time exceeds the bearing capacity of that wire, it will get heated up. This is known as overloading. Fuse a safety device can prevent the circuit from overloading and short circuiting. Very Short Answers (1 Mark) 1. What is the frequency of AC used in India? 2. Name the point where the iron filling are collected more when sprinkled around a bar magnet. 3. Who discovered electro magnetic induction? 173 [Class-X – Science] 4. Why does a compass needle get deflected when brought near the bar magnet? 5. If both the coil and the magnet are stationary, will there be deflection in galvanometer? 6. Why magnetic field lines do not intersect each other? 7. What is the advantage of Alternate Current over Direct current? 8. What do you understand by short circuiting? 9. When the force experienced by a current carrying conductor placed in a magnetic field is maximum? 10. Write the factors affecting the magnetic field due to a straight conductor? Short Answers (2 Marks) 1. A charged particle enters at right angles into a uniform magnetic field. What is the nature of charge particle, if it experiences a force in a direction pointing vertically out of the page. Magnetic field Charge particle (use left hand flemings rule) 2. Name the Rule– (a) Force experience by a current - carrying conductor placed in a magnetic field. (b) Direction of magnetic field lines associated with a current carrying conductor. (c) Direction of induced current in a coil due to its rotation in magnetic field. 3. What is solenoid? Where the magnetic field is uniform in solenoid? 4. Draw the pattern of magnetic field lines due to current carrying straight conductor? [Class-X – Science] 174 5. Name two safety measures commonly used in electric circuit and appliances? 6. What is overloading? 7. What is an earth wire? How it works in our domestic circuit? 8. If the current in a wire is flowing in the vertically downwards direction and a magnetic field is applied from west to east. What is the direction of force on the wire? Long Answer (5 Marks) 1. Explain the phenomenon of Electro magnetic Induction with the help of an activity. Write its one application. 2. Draw the schematic diagram of domestic circuit. Write the colour and function of Neutral wire, Live wire and Earth wire. 3. What is an electro magnet? Which material is used for making core of an electromagnet? Can we use steel as a material for core of the electromagnet? 175 [Class-X – Science] CHAPTER – 14 SOURCES OF ENERGY Energy comes in different forms and one form can be converted to another. For example if we drop a plate from a height, the potential energy of the plate is converted mostly to sound energy when it hits the ground. If we light a candle, the process is highly exothermic so that the chemical energy of the wax is converted into heat energy and light energy on burning. A Good Source of Energy would be one which has high calorific value be easily accessible be easy to store and transport be economical SOURCES OF ENERGY Conventional Source of Energy Non-Conventional Source of Energy Fossil Fuels Eg. Coal & Petroleum Thermal Power Plant Hydro Power Plants Bio-Mass bio gas plant Wind Energy Solar Energy E.g. Solar Cooker, Solar Cell Panel Energy From the Sea Eg. Tidal & wave energy, O.T. Energy Geothermal Energy Nuclear Energy. Among the sources of energy, some of them get exhausted (NonRenewable) While some of them do not get exhausted, therefore called as Renewable source of energy. Examples: [Class-X – Science] 176 1. Non Renewable source of energy Coal, Petroleum, Natural Gas 2. Renewable Source of energy Air, Water, Solar radiation, Geothermal Energy, ocean waves etc. Conventional Source of Energy 1. Fossil Fuels : Fuels developed from the fossils. e.g. Coal & Petroleum. Formed over million of years ago have only limited reserves These are non-renewable source of energy India has about 6% share in the world reserved coal, that may last 250 years more at the present rate of consumption. Disadvantages of Burning Fossil Fuels Released oxides of Carbon, Nitrogen, Sulphur (acidic in nature) cause Air pollution & Acid rain & green-house effect. Pressure Cooker Heat (Fossil Fuel) Bulb Dynamo Tennis Ball fitted with metal plate A Model of Thermo Electric Production. The Tennis ball having three slits filled with semicircular (plaster or Matallic) tins is our Turbine for generating electricity. Actually the steam produced impart energy to rotor of turbine which can move shaft of the generator to produce electricity. A very large amount of fossil fuels are burnt in Thermal Power Plant to heat up water to produce steam. Hydropower Plants convert the potential energy of falling water into Electricity since there are few water-falls which could be used as a source of potential energy, hence this is the reason, a large number of dams are built all over the world. 177 [Class-X – Science] Around 25% of our country’s energy requirement is met by Hydro Power Plants Dams are constructed to : Prevent flooding of river, provide water for irrigation & to generate hydroelectricity. Disadvantages of construction of Big Dams 1. Submerging/Loss of large variety of Flora fauna and human settlements & rotting of submerged vegetation release green house gas (CH4). 2. They pose dangers of earthquakes, landslides etc. 3. Biomass is Agricultural & animal wastes that can be used as a fuel. E.g. of Biomass – Firewood, cattle dung, sewage, dry leaves, stems & bagasse. Normally biomass has low calorific value & produce lot of smoke when they are burnt. Their efficiency as a good fuel has been increased tremendously with the application of technology. For e.g. cowdung becomes efficient & cheap good fuel in a Bio-gas plant. Charcoal is better fuel than wood because it does not contain water & other volatile material which are present in wood. [Class-X – Science] 178 Wood Limited Supply of O2 Charcoal Charcoal burns without smoke, flames & has high calorific value. Bio-gas is an excellent fuel & contains 75% of Methane (CH4). It burns without smoke, leaves no residues like ash, with high heat capacity. Biogas is produced by anerobic decomposition of the slurry (cowdung + water mixture) by microbes. This process is applied in a Bio gas plant. Gas Outlet SLURRY Manure Soil Gas Tank Digestor The Biogas is stored in the gas tank from which they are drawn through pipes for use in a Bio-gas plant Bio gas is used for lighting, cooking in the rural areas. While the slurry left behind is used as excellent manure, rich in nitrogen and phosphorous The large scale use of Bio-wastes & sewage material provide a safe and efficient method of waste-disposal besides supplying energy and manure. 179 [Class-X – Science] WIND ENERGY Unequal heating of the landmass and water bodies by solar radiation generates air movement & causes winds to blow. This kinetic energy of the wind can be used to do work. This energy is utilised to lift water from the well & to generate electricity in the wind mill. Actually the rotatory motion of the windmill is used to turn the rotor of the turbine which then generate electricity through Dynamo. The output of a single windmill is quite small so a number of windmills are erected over a large area - called wind energy farm. India Ranked Fifth in the world in harnessing wind energy for the production of electricity. It is estimated that nearly 45,000 MW of electric power can be generated if India’s wind potential is fully exploited. The minimum wind speed for wind mill to serve as a source of energy is 20KMPH. Advantages of Wind Energy 1. Eco friendly 2. Efficient source of renewable energy. 3. No recurring expenses for production of electricity Limitations of Wind Energy 1. Wind energy farms need large area of land 2. Difficulty in getting regular wind speed of 15-20 KmPH. 3. Initial cost of establishing wind energy farm is very high. 4. High level of maintenance of blades of wind mill. [Class-X – Science] 180 Non-Conventional Sources of Energy Solar Energy The energy emitted by the sun in form of heat and light is called solar energy. Solar Constant = 1.4 (kJ/s.m2) Outer edge of the earth receives solar energy equal to 1.4 kJ/s.m2 which is known as solar constant. Solar Energy Devices A large number of devices that utilize solar energy directly like : (i) Solar Cooker (ii) Solar furnaces (iii) Solar cells (iv) Solar water heaters Solar Heating Devices Use black painted surface because black surface absorbs more heat as compared to white or other surface. Use of glass plate because it allows shorter wave lengths infrared radiations to enter through it but doesn’t allow the infrared radiations to exit through it, causing more green House effect that results in increase in temperature. SOLAR COOKER Box Type Solar Cooker It consists of a rectangular box which is made up of material such as plastic or wood. Box is covered with black sheet and its inner walls are painted black to increase heat absorption. 181 [Class-X – Science] Solar cookers are covered with glass plate and have mirrors to focus the rays of the sun and achieve a higher temperature. PLANE MIRROR INNER METALLIC BOX GLASS COVER BLACK CONTAINER WOODEN BOX SOLAR COOKER (Box Type) Advantages 1. Use energy which is available in plenty (Solar Energy) 2. Is pollution free. 3. More than one food can be cooked simultaneously Disadvantages 1. Cannot be used for frying or baking purpose. 2. Food cannot be cooked at night or on a cloudy day. 3. Direction of reflector of solar heating has to be changed from time to time to keep it facing the sun SOLAR CELLS Solar cells are device that convert Solar energy into electricity. Develops a voltage of 0.5 – IV and can produce about 0.7W of electricity. Advantages of Solar Cell 1. Require a little maintenance [Class-X – Science] 182 2. Have no moving part. 3. No focussing device is required 4. Can be set up in remote areas. 5. Environment - friendly i.e. do not cause pollution. Disadvantage of Solar Cells 1. It require high cost 2. Efficiency is low 3. Initial cost of installation is quite high. Uses of Solar Cell 1. Used in calculators, watches etc. 2. Used in artificial satellites and space probes. 3. It is used in radio or wireless transmission system. SOLAR PANEL A large number of Solar Cells connected to each other in an arrangement is called solar panel. Material used for Making Solar Cells Silicon Silver is used for inter connection of cells. ENERGY FROM THE SEA OR OCEAN The energy from the sea is available in the following forms: (i) Energy of sea waves (ii) Tidal energy (iii) Ocean Thermal Energy. 183 [Class-X – Science] (i) Energy of Sea Waves The waves are generated by the strong winds that blows across the sea. The kinetic energy of this moving water rotates the turbine of a generator Limitation When strong winds stop blowing, the generator stops producing electricity (ii) Tidal Energy The tidal energy possessed by water during tides. The tides are caused due to gravitational force of attraction exerted by the moon on the water of the ocean. This form of energy is harnessed by constructing a dam across a narrow opening to the sea. A turbine fixed at the opening of the dam converts tidal energy to electricity. (iii) Ocean Thermal Energy The power plants used to harness the ocean thermal energy is known as “Ocean Thermal Energy Conversion Plant” (OTEC) Temperature difference between surface water and water at the depth of 2km should be 20°C or more. The warm surface water is used to boil ammonia (liquid) The vapours of the liquid are used to run the turbine of generator. The cold water (from deeper layers) is pumped up to condense the vapour into liquid. Geothermal Energy 1. Energy stored as heat inside the earth 2. The steam of underground water is taken out by sinking pipes through holes drilled in the earth’s crust. The steam under high pressure is used to rotate the turbines of the generator to produce electricity. [Class-X – Science] 184 NUCLEAR ENERGY Nuclear energy is the energy which is stored in the nucleus of an atom. Nuclear energy is of two types (i) Nuclear fission nucleus of a heavy atom (Uranium) when bombarded with low energy neutron split (break down) into lighter nuclei and huge amount of energy is released (ii) Nuclear Fusion When two lighter nuclei join up to form heavy nucleus and tremendous amount of energy is released. Nuclear fission process is utilized in nuclear reactors to produce electricity. Major Nuclear power plants : Tarapur, Rana Pratap Sagar, Kalpakkam. Advantages of Nuclear Energy 1. Large amount of energy is released. 2. In nuclear power plant, the nuclear fuel is inserted once to get energy over a long period of time. Disadvantages of Nuclear Energy 1. High cost of installation. 2. Environmental contamination may occur due to improper nuclear waste disposal. How long will energy source last Continuous use of non-renewable source of energy is a matter of concern because ultimately the deposit of these sources will be completely finished on the other hand renewable sources of energy will last forever e.g sun as a source of energy will be available for a very long period of time. 185 [Class-X – Science] Very Short Answers Type Questions (1 Mark) 1. What is a good source of energy. 2. Expand CNG and LPG 3. What is the minimum wind velocity required to obtain useful energy with a wind mill? 4. Name the main constituent of biogas. 5. Give two examples of fossil fuels 6. Name the device which directly converts solar energy into electric energy. 7. What does “OTEC” stand for? 8. What is nuclear energy? 9. Which one out of these is renewable source of energy solar energy, coal, petroleum, bio gas. 10. Which source of energy would you use to heat your food and why? 11. What are ‘‘Hot Spots’’? Short Answers Type Questions (2 or 3 Marks) 1. State two disadvantages of using fossil fuels as a source of energy. 2. Write two disadvantages of constructing high rising dams. 3. Give (i) two limitations and (ii) two advantages of wind mill. 4. Name any three forms of energy of the oceans which can be converted into usable energy forms. Describes how it is done in each case. 5. Explain the working of biogas plant with the help of labelled diagram 6. Explain the principle on which the solar cooker works. [Class-X – Science] 186 7. Write the advantages and disadvantages of using a solar cooker. 8. How does hydro electric power plant operate? Draw diagram 9. How is Charcoal produced? Why is it a better fuel then wood? Long Answer Type Questions 1. (5 Marks) (a) Why is the solar cooker box covered with plane glass plate? (b) Why is nuclear fission reaction considered better. (c) Use of wood as a domestic fuel is not considered as good. State two reasons for it 2. Distinguish between renewable and non renewable sources of energy? Which one of them you consider as better? Why? 3. Describe the construction and working of a biogas plant (fixed door). Write any two uses of Biogas. Also, any two advantages of Bio-gas. 187 [Class-X – Science] CHAPTER – 15 OUR ENVIRONMENT Environment means everything which surrounds us. It may include living (biotic) and non-living (abiotic) components. Biotic : Plants and animals. Abiotic : Air, water etc. Environment affect the life and development of an organism in its natural habitat & vice a versa. Substances that can be decomposed by the action of micro-organism like bacteria are called bio-degredable. E.g. organic wastes. Substances which cannot be decomposed by the action of microorganisms are called non-biodegradable. Example of biodegradable wastes : cattle dung, cotton, jute, paper, fruit and vegetable peels, leaves etc. Examples of non-biodegradable wastes : plastics, polythene bags, synthetic fibres, metals, radioactive wastes. ECO SYSTEM & ITS COMPONENT All the interacting living organisms in an area together with non living components form an ecosystem. So an ecosystem consists of both biotic (living creatures) and abiotic components like temperature, rainfall, wind, soil etc. [Class-X – Science] 188 Ecosystem Man-made Ecosystem Eg. Crop-field, Aquarium etc. Natural Ecosystem Aquatic Ecosystem Marine Ecosystem Eg. Sea, Oceans Terrestrial Ecosystem land Ecosystem Eg. Forest, Desert, Grassland etc. Fresh water Ecosystem River, Lake, Pond, pool All living organisms are classified on the basis nutrition. I. Producers : All green plants, blue green algae can produce their food (Sugar & starch) from inorganic substance using light energy (Photosynthesis). II. Consumers : Include organisms which depend on the producers either directly or indirectly for their sustenance. Consumers depend on others for food. CONSUMERS Herbivores – Grass eaters Carnivores Flesh Eaters E.g. Cow, dear E.g. Lion, Tiger Parasite Live & feed on the host body E.g. Plasmodium Omnivores Feed on both plant and flesh. E.g. Crow III. Decomposers : Fungi & Bacterias which break down (decompose) the dead plant, animals complex compounds into the simpler one. Thus decomposers help in the replenishment of the natural resources. Food Chain : It is the sequence of living organisms in which one organism consumes another organism for energy. It is unidirectional (single directional). For Eg. T1 Grass T2 Dear T3 Lion A 3-step Food chain 189 [Class-X – Science] Food Web : It is a network of a large no. of food chains which are interconnected. Snake Eagle Frog Mouse Sparrow Insect Plant In a food chain, various steps where transfer of energy takes place is called a trophic level. The green plants capture 1% of sun’s energy. The flow of energy is unidirectional in a food chain. There is gradual decrease in the amount of energy from one trophic level to next trophic level in a food chain. Tertiary consumers 1kJ 10kJ 100kJ 1000 kJ Energy Secondary Consumer Primary Consumer Producer Energy Flow TROPHIC LEVEL 10 Percent Law : The energy available at each successive trophic level is 10% of the previous level. So only 10% of Energy is transferred to next trophic level while 90% of energy is used by present trophic level in its life processes. The conc. of harmful chemical increases with every next trophic level in a food chain. It is called Bio-magnification For e.g. Grass (10 ppm) DDT [Class-X – Science] Dear (200 ppm) DDT 190 Lion (5000ppm) DDT Maximum concentration of such chemicals get accumulated in human bodies. Since humans occupy the top level in any food chain. ENVIRONMENTAL PROBLEMS Changes in environment affect us and our activities change the environment around us. Environmental problems caused by humans: (a) depletion of the Ozone Layer and waste disposal. (b) pollution due to mismanagement of waste disposal. I. Depletion of Ozone Layer Ozone (O3) layer is largely found in the stratosphere which is a part of our atmosphere from 12 km – 50km above sea level. Ozone is a deadly poison at the ground level. Ozone is formed as a result of a following photochemical reaction. O2 UV (1800°A to 2000°A) O2 + O O+O (Splitting of molecular oxygen) O3 (Ozone) Ozone layer is a protective blanket around earth which absorbs most of the harmful U.V. (Ultraviolet) radiation of the Sun, thus protecting the living beings of the earth from health hazards like skin cancer, cataract in eyes, weaken immune system, destruction of plants etc. The decline of Ozone layer thickness in Antartica was first observed in 1985 and was termed as OZONE HOLE. Reason of Ozone Depletion Excessive use of CFCs (Chloro Flouro Carbon) a synthetic, inert chemical E.g. Freon which are used as refrigerants and in fire extinguishers, caused Ozone depletion in the upper atmosphere. A single chlorine atom can destroys 1,00,000 Ozone molecules. U.N.E.P. (United Nation Environment Programme) did an excellent job in forging an agreement to freeze CFC production at 1986 levels (KYOTO Protocol) by all countries. 191 [Class-X – Science] Garbage Disposal Industrialization and rise in demand of consumer goods have created a major problem in the form of wastes/garbage accumulation and its disposal especially in urban area. The different methods of solid wastes disposal commonly used around the world are. 1. Open dumping : A conventional method in which solid wastes dumped in selected areas of a town. It actually cause pollution 2. Land fillings : Wastes are dumped in low living area and are compacted by rolling with bulldozers 3. Composting : Organic wastes are filled into a compost pit (2m × 1m × 1m). It is then covered with a thin layer of soil. After about three months the same garbage filled inside the pit changes into organic manure. 4. Recycling : The solid wastes is broken down into its constituent simpler materials. These materials are then used to make new items. Even nonbio degradable solid wastes like plastic, metal can be recycled. 5 Reuse : A very simple conventional technique of using an item again & again. For e.g. paper can be reused for making envelops etc. Very Short Answers (1 Mark) 1. Define Biomagnification 2. Expand the term CFC & U.N.E.P. 3. Define Ozone hole 4. Which of the following is/are Biodegradable : plastic cups, cowdung, aluminium foil, cotton. 5. Define food web. 6. Define Ecosystem [Class-X – Science] 192 7. Which bag would you prefer for shopping and why? (i) Jute bag (ii) Polythene bag 8. Why is ozone layer important for the existence of life on earth? Short Answer (2 Marks) 1. Differentiate between Biodegradable and non biodegradable wastes. Give two examples. 2. Use of Kulhads was not environment friendly idea. Why? 3. Draw an Energy Pyramid showing different trophic level. 4. What is the advantage of disposable paper cup use over plastic cups? 5. How can we help in reducing the problem of waste disposal? Give any two methods. 6. What is role of decomposer in Ecosystem. 7. Give any two ways in which non biodegradable substance would affect the environment. 8. What are trophic levels? Give an example of a food chain and state the different trophic levels in it. 9. What will happen if we kill all the organisms of one trophic level? 10. Study the food chain given below : (i) Grass Grasshopper Frog (ii) Wheat Rat Snake Hawk Which of the two consumers frog/hawk will get more available energy and why? Short Answer (3 Marks) 1. State various modes of waste disposal. 193 [Class-X – Science] 2. Explain how harmful chemicals enter our body. 3. Why does concentration of harmful chemicals increase whereas energy level decrease, from lower to higher trophic level in a food chain? Long Answer 1. (5 Marks) (i) What is ozone? How is it formed. (ii) State the significance of ozone layer. (iii) Give reason for depletion of ozone layer. [Class-X – Science] 194 CHAPTER – 16 MANAGEMENT OF NATURAL RESOURCES Natural Resources Resources provided to us by nature Soil, air, water, forests wildlife, coal and petroleum are used by man for his survival. Types of Resources : (a) Exhaustible : present in limited quantity e.g. coal petroleum. (b) Inexhaustible : present in unlimited quantity e.g. air, water. Management of natural resources is needed for conservation of natural resources. There are National and International Laws and Acts to protect the environment. Ganga Action Plan : Multi Crore Project came in 1985 to improve the quality of Ganga Contamination of river water is indicated by the presence of coliform (a group of bacteria found in human intestine) and acidic water (can be tested by the ph paper). 1993-94 Total Coliform (MPN/100ml) Minimum found in Rishikesh 600-650MPN/100ml Minimum desired level 450MPN/100ml Maximum found in Kannauj 1400MPN/100ml MPN Most probable number. National Award for wildlife conservation – in the memory of Amrita Devi Bishnoi who lost her life in the protection of Khejri trees in Rajasthan alongwith 363 other people. 195 [Class-X – Science] Chipko Andolan : Movement originated in Garhwal in early 1970s that was the result of a grassroot level effort to end the alienation of people from their forest. Protection of Sal forest in West Bengal in 1972. Three R’s to save the environment. Reduce means use less Save the resource by not wasting them Recycle Segregate the waste that can be recycled and use to make required things. Reuse use the things again and gain. Reuse is better than recycling as it saves energy. Management of Natural Resources is necessary so that these may last for the generations to come and are not exploited for short term gains. Forest and wild life conservation – Forests are biodiversity hot spots. Biodiversity of an area is the number of species of different life forms like bacteria, fungi, flowering plants, insects, birds etc. Hotspot means an area full of biological diversity. – loss of diversity may lead to a loss of ecological stability/ecological imbalance. STAKE HOLDERS A person having interest or concern for some thing is called as stake holder. Stakeholders of forests : (their dependence on forests) Local People (dependent on forests for their survival) Forest Department (Govt. who owns the land and controls resources Industrialists (Who use various forest products) Wild life enthusiasts (who want to conserve nature) Sustainable Management Management of resources wisely to make them available for future generations. [Class-X – Science] 196 Water Water is a basic necessity for all terrestrial forms of life. Irrigation methods like dams, tanks and canals have been used in various part of India. Dams Advantages of Dams – Ensures adequate water for irrigation (sufficient to satisfy need). Generate electricity. Continuous supply of water in regions. Disadvantages No equitable distribution of water. Large no. of people displaced without compensation. Involves huge amount of Public money without giving proper benefits. Causes deforestation and loss of biological diversity. Water Harvesting : Collection of rain water and its utilisation for various purposes. Advantages of storing water in the ground : (a) It does not evaporate. (b) It spreads out to recharge wells. (c) It provides moisture for vegetation over a wide area (d) It does not provide breeding grounds for mosquitoes. (e) It is protected from contamination by human and animal waste. 197 [Class-X – Science] Various ancient methods of water harvesting Method State Khadin, tanks, nadis Rajasthan Bandharas, tals Maharasthra Bundhis Madhya Pradesh and U.P. Pynes, ahars Bihar Kulhs Himachal Pradesh Ponds Jammu Region Eris (tanks) Tamilnadu Bawlis – Old method of water harvesting in Delhi and near by region. COAL AND PETROLEUM Coal and petroleum are non-renewable natural resources. Coal was formed from the remains of trees buried deep inside the earth some 500 million years ago. Petroleum is formed by the bacterial decomposition of dead marine plants and animals (burried at the bottom of the seas. This decomposition takes place under high pressure and temperature and formation of petroleum take millions of years of time. Coal and petroleum are called fossil fuels. Very soon coal and petroleum will be exhausted. At present rate of usage, petroleum will last us for about 40 years and the coal resources will last for another 200 years. Harmful effects of using fossil fuels: * Combustion of coal and hydrocarbons release a large amount of carbon monoxide, carbon dioxide, sulphur dioxide, oxides of nitrogen, etc. These cause air pollution and cause various diseases like respiratory and throat problems congestion etc. [Class-X – Science] 198 * Q.1 Excessive emission of green house gases like carbon dioxide cause a rise in atmospheric temperature (Global Warming). Why should we use fossil fuels judiciously? Ans. Fossil fuels are limited and exhaustible. Once exhausted, coal and petroleum will not be available to us in near future because they are formed extremely slowly over a very long time. Q.2 Write the steps you can take to reduce the consumption of coal and petroleum. Ans. * Switch off electricity appliance when not needed. * Use public transport instead of private one. * Whenever possible, use solar cooker. * Use stairs to climb instead of lift. Very Short Answers (1 Mark) 1. Why is it necessary to conserve our environment? 2. Define sustainable development 3. Name any two exhaustible resources 4. What is the most conductive PH range for the life of fresh water plants? 5. List two advantages of water harvesting. 6. Why is reuse better than recycle? 7. Define biodiversity. 8. List two steps you would take to conserve electricity in your house. 9. Who are called stake holders? 199 [Class-X – Science] 10. Name some traditional water harvesting systems in India. Short Answers (2 Marks) 1. How is mining is a cause of pollution? 2. Make a list of four forests products that we use. 3. How is burning of fossil fuels affecting our environment? 4. Suggest two measures for controlling CO2 levels in atmosphere. 5. Why should we conserve forest and wild life? Short Answers (3 Marks) 1. What are the three main problems from dams? 2. How can you reduce energy consumption at your level. Suggest at least three points. 3. Explain ‘Reduce’, ‘Recycle’ and ‘Reuse’. Long Answers (5 Marks) 1. What is the main objective of water harvesting techniques? Name an ancient water harvesting structures used in India. Mention 3 causes for failure to sustain water availability under ground? 2. Discuss the damage caused to forest by the following activities: (a) Building rest houses for 10% tourists in national parks. (b) Grazing domestic animals on National Parks. (c) Tourists throwing plastic bottles, covers and other things in National Parks. [Class-X – Science] 200 Answers in Brief 1. Curding. 2. 2Mg + O2 2MgO 3. Decomposition 4. Hint : oxidation occurs 6. Redox 7. Endothermic 8. Displacement of Cu Electric 9. H2O 2H2+O2 Current 10. To prevent oxidation of fats and oils. B2(a) 4H2 + N2 2NH4 (b) 2K + 2H2O 2KOH + H2 3(i) Oxidised Na (ii) Oxidised H2 Reduced CuO 6(i) Double displacement (ii) 3BaCl2 + Al2(SO4)3 2AlCl3 + 3BaSO4 201 [Class-X – Science] C1(a) 2ZnCO3 2ZnO + 2CO2 (b) 2Al + 3Cl2 2AlCl3 (c) Mg + 2H2O Mg(OH)2 + H2 D1(a) 2KClO3 2KCl + 3O2 (b) 2NH2 + 5O2 2NO2 + 6H2O (c) Na2O + H2O 2NaOH (d) Na + H2O NaOH + H2 (e) 2FeCl3 + 6NaOH 2Fe(OH)3 + 6NaCl Answers of Short Questions 1. Solution A 3. Calcium-oxy-chloride 4. Strong Acid H2SO4 Weak acid CH3COOH 6. CO2 8. Pop Sound + (Hint) 10. Washing Soda Na2CO3 Baking Soda NaHCO3 B6. Neutralisation Reaction [Class-X – Science] 202 eq- HCl + NaOH NaCl +H2O 9. Chlor-Alkali Process 10. Hint neutralises HCl in ourbody. C2(i) Acid + Metal Salt + H2 H2 (ii) NaOH + Zn Na2ZnO2 + H2 D2(a) Acid + Base Salt + Water (b) Acid + Metal Salt + H2 (c) Na2CO3 + 2HCl 2NaCl + H2O + CO2 NaHCO3 + HCl NaCl + CO2 + H2O (d) NaOH + H2O Na+ + OH– (e) Na2CO3 + 10H2O Na2CO3 . 10H2O 3(i) X Sodium Hydrogen Carbonate (NaHCO3) (Hint :) 1. Silver, Hg 2. Zn more reactive (Hint) 3. Brass, Bronze 4. Iodine 203 [Class-X – Science] 5. Which react with both acids and bases to form salt and water. eq - Al2O3 7. Acidic Element is Metal 9. Hint : - Strong inter -ionic attraction. 10. Gold, Silver D 1(i) Mg>Al>Zn>Fe>Cu A 1. Hint : Sharing of valence electrons. 2. Hint : Sharing of electrons between H and O H X O X H 8. Propanone CH3COCH3 10. C6H10 B 7. Pentanal H H H H H C C C C C H H H H O Methanoic Acid H C O [Class-X – Science] 204 OH H D2(i) A is CH3COOH - Acetic Acid (ii) B - is Ester CH3COOH + C2H5OH CH3COOC2H5 + H2O (iii) Used in perfumes, cakes etc. (iv) 2CH3COOH + Na2CO3 2CH3COONa + CO2 + H2O (Gas is CO2) (v) Hint : Dilution. A (i) Ca, Sr, Ba 4. Hint : third period indicates M shell with max. capacity of 2n2 i.e. 8 electrons. 5. Na, K. 9. 18 vertical columns (groups), 7 horizontal rows (periods) B 2. Hint : (Atomic size increases as we more down a group) D 3. a. A, B and C, D b. A and C, B and D c. C - more reactive. 205 [Class-X – Science] V.S.A. 1. 0° 2. Virtual, erect and magnified. 3. Shaving, by dentists. 4. f = +15 cm. 5. m hi –v ho u 6. Between O and F. (O F B A i 7. F C ABC i CBF r 8. 2F1 F1 O [Class-X – Science] F2 2F2 206 9. 10. 1Dioptre 1 focal length (1m) 1 1 (1m) Speed of Light changes 11. Take an object at infinity, after refraction, where the image is formed, is focus of convex lens. S.A. i r 1. c 2. n c v 1.54 3 108 v v 3 108 1.54 = 2×108 m/s 3. 1 1 1 f v u 1 1 1 6 v –12 207 [Class-X – Science] on solving v = +4 m. –v u m –4 1 –12 3 Virtual, erect and small 4. 1 1 1 – f v u 1 1 1 – –15 –10 u 1 –1 u 30 u = –30 cm. 2F1 F1 O 5. P = P1 + P2 = 3.5 – 2.5 = 1 D. f 1 1 1m. P 1 8. P = Px + Py 5 100 1 13 f y fy 20 –3 100 8 [Class-X – Science] 208 F2 2F2 fy = –60 cm. Concave lens V.S.A. 1. Scattering of light 2. Near point –25 cm. Far point - Infinity 3. Ciliary muscles. 4. Because there is no atmosphere. 5. Bifocal lens. 6. Red, Blue, Green. 7. Real and inverted. 8. Splitting of light into its component colours. 10. Myopia, can be corrected by concave lens. 12. Retina V.S.A. 1(a) Ampere 209 [Class-X – Science] (b) Volt (c) Ohm. (d) Watt (e) KWh. 2. From positive to negative. 3. RA l If A= 1m2, l=1 m., then = R. 4. R l (length) 1 (Area of cross section) on nature of material A 5. Volt meter in parallel Ammeter in series ( 6. Loss of kinetic energy of electron. 9. P = V I 10. 1 KWh = 3.6 × 106 J. S.A. 1. 3 – + 3 ( 9V [Class-X – Science] 210 ( 3 2. V = I R V I 3. H = I2 R t 4. R l A R (2 l) A 2 R 4R Resistance four times Resistivity No. change 5. P = VI I P 200 W 100 9.1A V 220 V 11 It requires fuse of 10A. 6 (i) A 1 1 R 1 3 3 5 R 3 (ii) 1 1 1 R 6 6 1 1 R 3 R 3 211 [Class-X – Science] (iii) R = 1 + 1 + 2 = 4 7. Rate at which heat is produced is called Power = I2 R = (2.5)2 × 200 = 1250 Watt 8. Parallel. 9(a) Three times (b) One-fourth S.A. 1. SI Unit of resistivity Ohm m l R r2 20 2 106 3.14 0.15 0.15 20 3.14 0.15 0.15 2 106 7.01 10–7 Ohm.m. 2(a) 1 1 1 R 6 6 R 3 (b) I V 6 R 3 I = 2A (c) V(across 4 ) I R =1×4 = 4V. [Class-X – Science] 212 V(across 2 ) 1 2 = 2V.. 3(a) R = 10 (b) R 30 31 V.S.A. 1. 50 Hz. 2. At poles. 3. Faraday 5. No. 9. When conductor is placed perpendicular to magnetic field. S.A. 2(a) Fleming's left hand rule. (b) Right hand thumb rule. (c) Fleming's right hand rule. 5. Fuse and earthing L.A. 2. Neutral wire – Black Live wire – Red Earth wire – Green 213 [Class-X – Science] V.S.A. 2. C.N.G. Compressed Natural Gas LPG Liquified Petroleum Gas 3. 15-20 Km/h. 4. Methane (CH4) 5. Coal and petroleum 6. Solar Cells 7. Ocean Thermal Energy Conversion Plant 9. Solar energy [Class-X – Science] 214 (UNSOLVED) SAMPLE PAPER-I Time : 3 hrs. Max. Marks = 90 CLASS X Very Short Answers Type Questions 1. Write balanced chemical equation for the reaction taking place when limestone is heated strongly? 1 2. A copper wire has a resistance R and specific resistance ‘P’. It is stretched to double its initial length. How will its (i) resistance; (ii) specific resistance be affected on stretching? 1 3. V-I graphs for series and parallel combinations of two metallic resistors are as shown, which one of the two represents parallel combination? 1 A B I V 4. When a solution of potassium chloride is mixed with silver nitrate solution, an insoluble white substance is formed. Write the balanced chemical equation for the reaction and also name the type of chemical reaction. 2 5. How is the colour change observed? A drop of litmus solution is added to each of the four solutions given below. State the colour of litmus solution observed in each: 2 215 [Class-X – Science] Soap Solution, Sodium Carbonate Solution, Vinegar, Lemon Juice. 6. How does the strength of the magnetic field at the centre of a current carrying circular coil of a wire change on : (a) increasing the radius of the coil; (b) decreasing the number of turns in the coil. Justify your answer in each case. 2 7. What are the final products of Carbohydrates, Proteins and Fats after their digestion? 2 8. Two identical immersion heaters are to be used to heat water in a large container, which one of the following arrangements would heat the water faster: 3 (i) Connecting the heaters in series with main supply. (ii) Connecting them in parallel with the main supply. Give reason for your answer. 9. Explain reflex arc and reflex action with the help of a labelled diagram.3 10. Explain why: 3 (a) Respiration is an exothermic reaction. (b) All decomposition reactions are endothermic reactions. (c) When blue salt of copper sulphate is heated, it becomes colourless. 11. A student wrongly draws the given circuit diagram for verification of Ohm’s Law. Assume that voltmeter and milliammeter are ideal in nature. 3 + – – V+ – mA + [Class-X – Science] 216 Answer the following questions based on above circuit diagram: (i) What will be the voltmeter and ammeter readings in this case and why? (ii) Point-out two major mistakes made by the student in drawing the circuit diagram. (iii) Re-draw the circuit diagram correctly. 12. A gas is produced when Conc. H2SO4 is added to solid sodium chloride solution taken in a test tube. The gas coming out through the delivery tube is passed over a dry litmus paper and then over a moist blue litmus paper. What would you observe? Give reason for your observation and write the corresponding balanced chemical equation. 3 13. Name various forms of energy available from the sea. Write any three limitations in harnessing these energies. 3 14. Name the type of chemical reaction represented by the following equations: 3 (i) CaCO3 CaO(s) + CO2 (g) (ii) CaO(s) + H2O(l) Ca(OH)2 (aq) (iii) Zn(s) + H2SO4 (aq.) ZnSO4 (aq.) + H2(g) 15. Study the given circuit diagram and answer the following questions:3 K1 + – + A 10 15 K2 – V + (i) What will be ammeter reading and voltmeter read when only key K1 is closed. 217 [Class-X – Science] (ii) What will be the current flowing through 10 and 15 when both K1 and K2 are closed? (iii) What will be the ammeter reading and voltmeter readings when both keys K1 and K2 are closed? Support your answer in each case with mathematical calculations. 16.(a) Out of two solar cookers, one was covered with a plane glass slab and the other was left open. Which of the two be more efficient and why?3 (b) List any two disadvantages of using biomass as a fuel. 17. A junior scientist in a leading dental cream manufacturing company discovers that the addition of a certain element to a dental cream can bring about a significant improvement in the quality of product in controlling tooth diseases. However, she also discovers that the same element can also result in one in a million cases of user, getting a deadly disease. The scientist reports her results in full in the Board’s meeting. Assuming that you are the CEO of the company, answer the following questions on the basis of above information: 3 (i) Should the company go ahead with manufacturing the product without bothering or sharing the ice-effects of the product? Give reasons for your answer. (ii) How will you respond to a suggestion from a colleague that the company should do more research for reducing the ice effects before manufacturing the product? (iii) Which values are promoted through this anecdote? 18.(a) Match the type of electric current on its source voltage in column-I with all the correct statements in Column-II. 3 Column I 1. Column II Direct current changes periodically. [Class-X – Science] (i) Its direction of flow in a circuit 218 2. Alternating Current ii) Its magnitude changes continuously. (iii) Its direction of flow in a circuit always remains same. (iv) Its magnitude always remains same. (v) Its frequency is zero. (vi) Its frequency in India is 50 Hz. (vii) It can be used for producing heat in a metallic conductor. (viii) Its source voltage cannot be used for carrying out electroplating. 19. Explain electrolytic refining of impure of copper with the help of a labelled diagram. 5 20. Draw the diagram of human heart and label. 5 (a) The parts which (i) receive deoxygenated blood from nenacava. (ii) send deoxygenated blood to lungs through pulmonary artery. (iii) receive odygenated blood from lungs and; (iv) send oxygenated blood to all parts of body through aorta. (b) What does the blood consist of? (c) Write two functions of blood. 21.(a) State Flemings’s Right hand rule. 5 (b) A coil of insulated copper wire is connected to a Galvanometer. What will be observed if a bar magnet is (i) Pushed into the coil. (ii) Withdrawn from inside the coil; (iii) held stationary inside the coil? 219 [Class-X – Science] Give reasons for your answer. (c) State two factors on which magnitude of the induced current produced in a coil depend when a magnet is brought into the coil. 22. What causes rusting of iron? Design an activity to show the conditions needed for iron nails to get rusted. Why do we paint these articles?5 23.(a) What causes tendril to encircle on coil around the object in contact with it? Explain the process involved. (b) What is Chemotropism? Give one example. 5 24(a) What is the chemical name of Baking Soda? Write the chemical reaction involved in its preparation write its one use. (b) Give the chemical names of acids present in (i) ants; (ii) lemon; (iii) milk; (iv) tomato. 25. Iron filings were added to a solution of CuSO4. After 10nun, it was observed that the blue colours of solution has changed and a layer has deposited on iron filings, which one of the following set of colours correspond to the colour of the solution and the colours of coating respectively? 5 (a) Yellow and Green (b) Brown and Blue (c) Red and Greenish Blue (d|) Light Green and Reddish Brown 26. A student connects a circuit to study Ohm's Law using a resistor of 3 and battery eliminator of 6v. Which of the ammeter should be chosen to read the value of current for this circuit, if ammeters available in the lab have following ranges? [Class-X – Science] 220 (a) 0-200mA (b) 0-100mA (c) 0-1A (d) 0-2A 27. While performing the experiment of Ohm’s Law a student has plotted the following graph. The resistances of the conductor will be : 5 90 MA 60 I 30 .3 .6 V (vott) .9 (a) 1000 (b) 10 (a) 100 (d) 1 28. The range of a voltmeter is 0 to 2.0V, If it has 20 divisions between 0 mark and .5V mark, the least count is 5 (a) .020V (b) .025V (c) .050V (d) .250V 29. In an experiment to show that sunlight is necessary for photosynthesis, the leaf is boiled in alcohol for a few minutes using a water bath. It is essential to use a water bath because: (a) alcohol is highly volatile. (b) steam heats, the leaf rapidly. (c) steam dissolves chlorophyll (d) Alcohol is inflammable. 30. Which structure out of I, II, III and IV marked in the given diagram should be labelled as Stoma? 5 221 [Class-X – Science] III I II IV (a) I (b) II (c) III (c) IV 31. A student adds a few drops of universal indicator to an aqueous solution of sodium hydroxide. He would observe that the colour of the solution changes from (a) colourless to red (b) colourless to blue (c) red to blue (d) blue to red 32. Two resistors R1 and R2 are to be connected in parallel combination. Select the correct combination is R1 R1 R1 + – + R2 R1 R2 R1 – R2 p q r (a) only p (b) only q (c) only r (d) All of the above. 33. In the circuit below the voltmeter and ammeter readings would be respectively: (a) 3V and 1A (b) 3V and 1A (c) 1V and 3A (d) 3V and 3A [Class-X – Science] 222 + – V 6 6 + – A 3V 34. A black strip of paper was clipped on to a destarched leaf in a potted plant to cover a part of the leaf. The plant was then exposed to sunlight for four hours. The paper strip was removed and the leaf tested for starch. When iodine solution was added 5 (a) Entire leaf turned blue-black. (b) Covered part of leaf became blue-black. (c) Uncovered part of leaf became blue-black. (d) Color of iodine solution remained unchanged. 35. While preparing a temporary stained mount of a leaf epidermal peel, the extra stain is removed by 5 (a) Washing with water (b) washing with calcium chloride (c) soaking with filter paper (d) absorbing with cotton wool 36. Four students measured the pH value of few samples and recorded their observation as follows: Student Water Acetic Acid HCl NaOH A 7 1 1 1 B 7 3 1 1 C 7 1 1 13 D 7 3 1 13 Which one of the following represents a correct measurement. 223 [Class-X – Science] (a) A (b) B (c) C (d) D 37. The current flowing through a conductor is 370 mA and p.d across its ends is 7.8V. The resistance would be 5 (a) .175 (b) 1.75 (c) 17.5 (d) 175 38. Four solutions I, II, III, IV were given to a student to test their acidic or basic nature using pH paper. He observed that pH paper turned to red, blue, green and orange respectively made by the student would be. 5 (a) I, II and III are acidic (b) I and IV are acidic (c) II, III and IV are acidic (d) II and IV are acidic 39. When a student added Zn granules to dil HCl a colourless and odorless gas evolved. On testing with a burning match stick it was observed that the match stick: 5 (a) continued to burn brilliantly (b) burnt slowly with a blue flame (c) extinguished and the gas burnt with pop sound. (d) continued to burn brightly and gas burnt with a pop sound 40. To determine the equivalent resistance of three restore arranged in parallel four students connected the resistors as shown in Fig. A, B, C, and D. The correct set up is that of (a) A (b) B (c) C (d) D [Class-X – Science] 224 R1 R2 R1 R2 R3 (A) R3 (B) R2 (C) R1 R3 R2 R3 (D) 41. The correct set of three precautions for setting up the experiment to demonstrate that CO2 is evolved during respiration is. 5 (a) Thread holding KOH test tube, airtight flask, delivery tube above water surface in the brakes. (b) Flask having just germinated seeds, airtight set up, delivery tube dipped in water in beaker. (c) Flask with water covered seeds, airtight set up, Kott tube held by a thick wire. (d) Just germinated seed under water in flask, delivery tube above water level, thread holding Kott test tube. 42. KOH pellets are used to absorb: (a) air in flask (b) moisture in flask (c) oxygen in flask (d) CO2 released by germinating seeds during respiration. 225 [Class-X – Science] (UNSOLVED) SAMPLE PAPER-II Time : 3 hrs. Max. Marks = 90 CLASS X 1. Why is photosynthesis considered an Endothermic reaction? 1 2. How is an ammeter connected is a circuit to measure current flowing through it? 1 3. Name the agent which decomposes animal dung into Bio Gas. 1 4. Using a suitable chemical equation justify that some chemical reactions are determined by : 2 (i) change in colour (ii) change in temperature 5. The wattage of a bulb is 24 watt when it is connected to a 12 V battery. Calculate its effective wattage if it operates on a 6 V battery. 6. Study the following Electric Circuit. + V 2 – 4 2 A – K1 3v + – + Find the reading of ammeter and the voltmeter. 7. How are lungs designed in human beings to maximise the area for exchange of gases? [Class-X – Science] 226 8. A browns substance ‘X’ on heating in air forms a substance ‘Y’. When hydrogen gas is passed over heated ‘Y’ it again changes back into ‘X’.3 (i) Name the substance X and Y. (ii) Name the type of chemical reaction occurring during both the changes. (iii) Write the chemical equations of the reactions. 9.(a) Oil and fat containing food items are flushed with N2 while packing them. Why? (b) Name any two amphoteric oxides. 10. What are strong and weak acids? Give one example for each. 3 11. A Gas ‘X’ reacts with lime water and forms a compound ‘Y’ which is used as bleaching agent. Identify X and Y. Give the chemical equation of reactions divided. 12.(a) Name the main ore of mercury. How is mercury obtained from its ore? Give balanced chemical equations. 3 (b) What is Thermite Reaction? How is it used to join the railway tracks or cracked machine parts? 13.(a) Define 1Kwh. Give its relation to 1Joule. 3 (b) When do you say that resistance of wires 1 Study the given circuit and find 3 6V A + – 10 6 3 227 [Class-X – Science] (a) Equivalent Resistance (b) current flowing through ammeter (c) Potential difference across 10 resistor. 15. State Ohm’s Law. Express if mathematically and apply it to define the unit of resistance. 3 16. Name two safety measures commonly used in electric circuits and appliance. What precautions should be taken to avoid the overloading of domestic electric circuits? 17(a) Differentiate between Sensury and Motor Neurons. 3 (b) How is brain protected in our body? (c) Name the part of brain responsible for precision of voluntary actions and maintaining body posture and balance of body. 18. List any six advantages a group of farmers will have also have set up a Bio-Gas plant close to their farms. 3 19. List any three advantages and limitations each of using a Solar Cookers.3 20.(a) A white coloured powder is used by the doctors for supporting fractured bones: 5 (i) Write chemical name of the powder. (ii) Write its formula. (iii) Write the chemical equation when this white powder is mixed with water. (b) If pH of the mouth of a person falls below 5.5. What changes will occur in his mouth? How can they be controlled? Write any two measures. 21. A metal E is stored under kerosene. When a small piece of it is left open in the air, it catches fire. When the product formed is dissolved in water it turns red litmus to blue. 5 (i) Name the metal E. (ii) Write the chemical equation for the reaction. [Class-X – Science] 228 22.(a) What is Electro Magnetic induction? 5 (b) Describe the various methods of producing induced current. (c) State the rule which gives the direction of induced current. 23. One day during lunch hour Om and Rohit started gulping food quickly. Kishore their friend told them to eat is slowly but they listen to him and went out to play. Om developed stomach ache while playing. 5 (i) What according to you might have gone wrong with him? (ii) What advice would you give to him? (iii) What values are promoted by Kishore? 24.(a)(i) If the cerebellum is not functioning properly, state the activities of our body that are affected. (ii) How do muscle cells show movement? (b)(i) Which hormone is secreted when growing plants detect light? (ii) How does this hormone help the shoot to bend towards light? 26. Two colours seen at the extreme ends of pH chart are: (a) Red and Blue (b) Red and Green (c) Green and Blue (d) Orange and Black 27. On putting a few drops of a liquid on a pH strip, the colour of the pH strip changed to red. This liquid is most probably: (a) NaHCO (b) HCl (c) NaOH (d) C2H5OH 28. Four drops of red litmus solution were added to each one of the following substances, which one turns red litmus solution blue? 229 [Class-X – Science] (a) Alcohol (b) Distilled Water (c) NaOH Solution (d) HCl 29. Zn pieces were placed in each of four test tubes containing different salt solutions as shown below: Aluminum Sulphate solution Zinc Sulphate solution Zn granules Zn granules Iron Sulphate solution Zn granules (a) I and II (b) I and III (c) III and IV (d) I and IV CuSO Solution Zn granules 30. The following ammeters and voltmeters are present in the lab to find equivalent resistance of two resistors R1, & R2 in parallel. Ammeters: A1 of Range 0 to 300mA: Least count 10mA A2 of Range 0 to 100 mA: Least count 20mA Voltmeter: V1 of Range 0 to 5V: Least count .2V V2 of Range 0 to 4V : Least count 04V The best combination of voltmeter and ammeter would be (a) A1 and V1 (b) A1 and V2 (c) A2 and V1 (d) A2 and V2 31. In a milliammeter there are 20 divisions between 400 mA mark and 500 mA mark. The least count of the milliammeter is (a) .5mA (b) 5mA (c) 10mA (d) 50mA 32. The current through a resistor connected in an electric circuit and the potential difference across its ends are shown in the diagrams. [Class-X – Science] 230 100 200 0 1 300 2 0 3 MA The value of the resistance of the resistor is (a) 25 (b) 20 (c) 10 (d) 15 33. Out of the two circuits shown here, the two resistors R1 and R2 have been correctly connected in series in R2 R1 R1 + V – A – A + V R2 – + – + + – + – (a) circuit A only (b) circuit B only (c) both A and B (d) neither of two circuits. 34. In an experiment to find the equivalent resistance of a series combination of two resistors R1 and R2 a student uses the circuit shown here. The circuit shown here. The circuit will give V A R1 R2 Battery eliminator 231 [Class-X – Science] (a) correct reading for voltage ‘V’, but incorrect reading for current ‘I’. (b) correct reading for current ‘I’, but incorrect reading for voltage ‘V’. (c) correct reading for both current ‘I’ and voltage ‘V’. (d) incorrect readings for both current ‘I’ and voltage ‘V’. 35. A stu d en t h as co n n ected th ree v o ltm eters acro ss th ree resistan ces R 1, R2 and R3 as shown in the circuit. Given that R1 < R2 < R3 write V1, V2, V3 in decreasing order of the readings shown by each of them. V1 R1 V2 V3 R2 R3 (a) V1, V2, V3 (b) V3, V2, V1 (c) V1, V3, V2 (d) V2, V1, V3 36. A voltmeter has a least count of .05V while doing Ohm’s Law experiment, a student observed that the pointer of the voltmeter coincides with 15th division. The observed reading is : (a) .75V (b) .075V (c) 7.5V (d) 75V 37. Before setting up an experiment to show that seeds release CO2 during respiration, the seeds should be: (a) Dried completely (b) boiled (c) soaked in vinegar (d) kept moist till they germinate 38. In an experiment on photosynthesis students were instructed to cover a portion of a leaf of a destarched potted plant with an opaque paper [Class-X – Science] 232 strip. Varun used a green paper strip. Vijay used white paper strip and Anshul used black paper strip. After four hours there will be no starch formation in the covered position in (a) Varun’s experiment (b) Vijay’s experiment (c) Anshul’s experiment (d) All of the above. 39. A student was asked to focus a permanent slide under the high power of a microscope. This involved (a) place the slide on stage (b) clean microscope & lens (c) Focus the material (cocuse adjustment) (d) place the low power objective lens (e) sharpen the focus with fine adjustment (f) Bring high power lens over slide. Put them in correct sequence (a) A, B, D, E, F, C (b) B, A, C, D, E, F (c) A, B, F, C, D, E (d) B, A, D, C, F, E 40. In the given diagram parts X & Y are: X Y X Y (a) Stomata Guard Cell (b) Guard Cell Stomata (c) Epidermal Cell Stomata (d) Stomata Epidermal Cell 233 [Class-X – Science] 41. While preparing a temporary mount of leaf epidermis it is suggested that a birch instead of a needle should be used to transfer the peel from petridish to slide. This is because: (a) Sharp needle does not mount the peel. (b) needles may damage the cells. (c) needle used to avoid entry of air bubble. (d) brush is more in length than needle 42. A student sets up the apparatus for experiment be show that O2 is released during respiration. After two hours he would observe: (a) Kott turning milky. (b) water level rising in the bent tube in beaker. (c) water level decreasing in the bent tube. (d) no change in water level in the bent tube. [Class-X – Science] 234 (UNSOLVED) SAMPLE PAPER-III Time : 3 hrs. Max. Marks = 90 CLASS X 1. What are the conditions that promote corrosion? 1 2. What is the SI unit of the Electrical Potential. 1 3. Name two alternative sources of Energy. 1 4. What is an Oxidation Reaction? Give an example. 2 5. What material is used in making the Filament of an Electric Bulb. Why? 2 6. Draw a diagram to show the magnetic field lines around a bar magnet? List any two properties of magnetic field lines. 2 7. Write two differences between Aerobic and Anaerobic respiration. 2 8. Balance the following equations: 3 (a) FeSO4 Fe2O3 + SO2 + SO3 (b) NaOH + H2SO4 Na2SO4 + H2O (c) MnO2 + HCl MnCl2 + Cl2 + H2O 9. On passing excess CO2 through lime water, it first turns milky and then becomes colourless. Explain why? Write the chemical reactions. 3 10. Three solutions A, B and C, when tested with universal indicator showed pH as 1, 11 and 7 respectively. Which solution is strongly acidic, strongly basic and neutral? Arrange the pH in increasing order of Hydrogen ion concentration. 3 235 [Class-X – Science] 11. A blue salt becomes white on heating. With the help of a reaction, explain the change in colour. 3 12. Give reasons for the following: 3 (a) Zinc can displace copper from copper sulphate solution. (b) Silver articles become black after some time when exposed to air. (c) A metal sulphide is converted to its oxide to extract the metal from a sulphide ore. 13. 4resistance wire is doubled on it. Calculate the new resistance of the wire. 3 14. A torch bulb is rated 2.5V and 750mA. Calculate 3 (i) its power (ii) Resistance (iii) the energy consumed if this bulb is lighted for 4 hours 15. How can three resistors of resistances 2, 3 and 6 be connected to give a total resistance of (a) 4 (b) 1 ? 3 16. Explain different ways to induce current in a coil. 3 17. Explain Reflex Are. 3 18. Write the problems faced in construction of big dams. 3 19. What is Biomass? Explain the working of a biogas plant using a labelled diagram. 3 20.(a) Metal compound ‘A’ reacts with dilute hydrochloric acid to produce effervescence. The gas evolved extinguishes a burning candle. Write a balanced chemical equation for the reaction if one of the compounds formed is calcium chloride. 5 (b) Why does distilled water not conduct electricity, whereas rain water does. [Class-X – Science] 236 21.(a) What do you understood by Alloy and Amalgam? 5 (b) Name the alloy used for Welding Electric Wire together. What are its constituents? (c) What are the constituents of Brass and Stainless Steel. State one property of these alloys which is different from its main constituents. 22. What is a Solenoid? Draw magnetic field lines due to a current carrying Solenoid. Write three important features of the magnetic field obtained.5 23. Draw a labelled diagram of respiratory system in human beings and explain the mechanism of breathing. 5 24.(a) Name of the parts of hind-brain and mention their functions. 5 (b) Name the plant hormone which is synthesised at the shoot tip. Explain briefly why does a plant shoot bend towards light. 25. On reaction of water with quick time (a) a hissing sound is produced (b) Both (a) and (b) are correct (c) Heat is produced (d) None is correct. 26. Which one of the following can be used to test the pH of a neutral solution? (a) Red litmus paper (b) Blue litmus paper (c) Phenolphthalein (d) Universal indication 27. When a drop of a solution ‘X’ is placed on a strip of pH paper, a deep blue colour is produced. This sample should be of (a) NaOH (b) Lemon Juice 237 [Class-X – Science] (c) Water (d) HCl 28. If a pH indicator paper is dipped in a grape juice solution, what will be the possible colour of the pH paper? (a) Deep Red (b) Blue (c) Orange (d) Violet 29. The colour of the coating developed on the Zinc Rod on dipping in the aqueous copper sulphate solution will be (a) Blue (b) Brown (c) White (d) Green 30. Volt is the unit of (a) Resistance (b) Potential difference (c) Current (d) Charge 31. In a series combination, which remains constant? (a) Current (b) Voltage (c) Both (a) & (b) (d) None 32. What is the equivalent resistance of three resistance of 2, 3, and 1, joined in series: (a) R = 6 (b) R = 1 (c) 1/R = 1 (d) 1/R = 1/6W-1 33. An ammeter has 20 divisions between mark 0 and mark 2 on its scale. The least count of the ammeter is (a) 0.02A (b) 0.01A (c) 0.2A (d) 0.1A 34. Keeping the potential difference constant, the resistance of a circuit os made four times by how much does the current change? [Class-X – Science] 238 (a) four times (b) becomes halted (c) becomes one fourth (d) remains unchanged 35. Three resistors of 2 and 3 are connected in parallels. The equivalent resistance of the combination will be: (a) greater than 3 (b) less than 1 (c) equal to 2 (d) between 1 and 3 36. Two filaments of same length are connected that in series and then in parallel. For the same amount of main current flowing, the ratio of the heat produced is (a) 2:1 (b) 1:2 (c) 4:1 (d) 1:4 37. Which stain would you suggest to observe stomata in a dicot leg? (a) Methylene blue (b) Acetocabnnine (c) Safranin (d) None of the above 38. Leaf peel mount is taken from which side of the leaf (a) Dorsal (b) Ventral (c) both (a) and (b) (d) None of the above. 39. Which of the following solution is used to test the presence of CO2 (a) Lime Water (b) Glucose Water (c) Alcohol (d) Salt Solution 40. The end products of respiration are (a) CO2 and N2 (b) CO2 and H2O (c) CO2, H2O and Energy (d) CO2, N2 and H2O 239 [Class-X – Science] 41. A leaf is boiled in alcohol before using iodine for starch test in order to (a) dissolve starch (b) soften the leaf (c) dissolve chlorophyll (d) make it react with iodine 42. The leaf should be covered with black paper (a) only on the dorsal surface. (b) only on the ventral surface (c) on both dorsal and ventral surfaces (d) None of these. [Class-X – Science] 240 (UNSOLVED) SAMPLE PAPER-I Time : 3 hrs. Max. Marks = 90 CLASS X 1. Draw a ray diagram to show the angle of deviation when a ray of light passes through a glass prism. 1. 2. Name the type of reaction represented by the following equation: 1 COHO CH3CH 2OH CH3COOH CH3COOC2 H5 H2 O H SO 2 4 3. In which part of female reproductive tract, fertilisation takes place. 1 4. Complete the diagram in your answer book and write the nature of image formed. 2 2F1 F1 O F2 2F2 5. An object is placed at a distance of 10cm. from a concave mirror. If its image is observed at 6cm from the mirror. Calculate the focal length of the mirror. 2 6. The construction of large dams lead to (i) Social and (ii) Environmental problems. List two problems in each case. 2 241 [Class-X – Science] 7. Explain the terms: 2 (i) Speciation (ii) Natural Selection 8. Define power of a lens and write its SI Unit. Two lenses of power 2.5D and +1.5D are placed in contact. Find the total power of the combination of lenses. Calculate the total length of this combination.3 9. A person is unable to see objects nearer than 50 cm. He wants to read a book placed at a distance of 25 cm. Name the defect of vision he is suffering from. How can it be corrected? Draw ray diagrams for (i) the defective eye (ii) its correction using a suitable corrective lens. 3 10.(a) With the help of a ray diagram show that when light falls obliquely on the side of a rectangular glass slab, the emergent ray is parallel to the incident ray. 3 (b) The refractive index of water for light going from air to water is 1.33. Find the refractive index of air for a beam of light going from water to air. 11. With the help of a labelled diagram, explain the following: 3 (i) The Sun appears reddish during sunrise. (ii) At noon, the sun appears white. 12. Which of the following compounds will undergo 3 (i) Addition Reaction: C2H6, C3H8, C3H6, C2H2 and CH4. (ii) What is Hydrogenation? State its industrial application? 13.(a) Atomic number is considered to be a more appropriate parameter than atomic mass for classification of elements in a periodic table. Why?3 (b) How does atomic size of elements vary on moving from: (i) left to right in a period (ii) top to bottom in a group. [Class-X – Science] 242 Give reasons for your answers. 14.(a) What are trophic levels? Give an example of food chain and state the different trophic levels in it. 3 (b) What is the role of decomposers in the Ecosystem? 15. How can you help in the problem of waste disposal? Give any three methods. 3 16. What does HIV stand for? Is AIDS an infections disease? List any four modes of spreading AIDS. 3 17.(a) Explain the terms: 3 (i) Implantation, (ii) Placenta (b) What is the average duration of human pregnancy? 18. What are Fossils? What do they tell us about the process of evolution?3 19. List two advantages of vegetative propagation? In which two of the following plants, the vegetative propagation practised? Banana, Rice, Tomato, Rose. 20(i) Under what condition, a concave mirror produces a virtual and magnified image? Draw a labelled ray diagram to show the formation of image in the above case. Also state the position of object to produce magnified and real image. 5 (ii) A ray of light moving along principal axis is falling on a concave mirror. Draw the path of reflected ray. Also state the values of angle of incidence and reflection in this case. 21.(a) Name the compound CH3COOH and identify its functional group. 5 (b) Give a chemical test to identify this compound. (c) Name of gas evolved when this compound acts on solid sodium carbonate. How would you identify this gas? 22.(a) How do we classify elements? 243 5 [Class-X – Science] (b) What were the two criteria used by Mendeleev in creating his periodic table? (c) Why did Mendeleev leave some gaps in the periodic table? (d) In Mendeleev’s periodic table, why was there no mention of noble gases like Helium, Neon and Argon? (e) Would you place the two isotopes of chlorine Cl-35 and Cl-37 in different slots because of their different atomic masses or in the same slot because of their chemical properties are the same. Justify your answer. 23.(a) What is the role of seminal vesicles and the prostate gland? 5 (b) What are the three categories of contraception methods? Write briefly about each. 24. After reading about Mendel’s experiment on sweet pea Renu wanted to repeat the same in his kitchen garden. She bought sweet pea seeds and swed them. After few months when the plants started flowering she observed that all plants were tall. 5 (a) Why all plants were tall? (b) Under which condition she could have observed both tall and dwarf plants. (c) If she collects seeds from her garden and sows them, what type of plants she is expected to get? 25. Which of the following cannot be used for the preparation of soap (a) Castor Oil (b) Mobil Oil (c) Groundnut Oil (d) Lirseed Oil 26. A red Litmus paper was half dipped in the mixture after the saponification reaction was complete. Which of the following observations is correct. [Class-X – Science] 244 (a) Red Red Red Red Green White Red Blue (b) (c) (d) 27. On stiring an oil with sodium hydroxide solution. (a) evolution of heat takes place (b) absorption of heat takes place (c) depends upon the oil taken (d) no heat change happens. 28. The following figure illustrates binary fission in Amoeba. Choose the option giving correct sequence (I) (II) (III) (a) I, IV, III, II (b) II, IV, I, II (c) IV, II, I, III (d) III, IV, II, I (IV) 29. Tick the correct statement: (a) More foam is formed by hard water than soft water. (b) More foam is formed by soft water than hard water. (c) Hardness of water is due to the presence of calcium hydrogen carbonate only. (d) Greater the amount of calcium sulphate in water, greater will be the cleaning capacity of soap. 245 [Class-X – Science] 30. While performing the experiment on tracing the path of a ray of light passing through a glass slab as shown in the given diagram, four students interpreted the results as given below. Which one of the four interpretations is correct i r r e (a) i > e > r (b) i > r > e (c) i = e < r (d) i = e > r 31. A student while observing the properties of acetic acid, would report that this acid smells like (a) vinegar and turns red litmus blue (b) rotten egg and turns red litmus blue (c) vinegar and turns blue litmus red (d) rotten egg and turns blue litmus red 32. A convex lens can form a virtual image of a real object if the object is placed. (a) between the lens and its focus. (b) at the focus of the lens. (c) at infinity. (d) at centre of curvature of lens. [Class-X – Science] 246 33. Acetic acid was added to four test tubes containing the following chemicals: (i) Sodium carbonate (iii) (ii) Blue litmus solution Lime Water (iv) Distilled Water Which amongst these is/are correct option(s) for carrying out a characteristic test for identification of a characteristic test for identification of a carbonylic acid (acetic acid) in the laboratory. (a) (i) only (b) (ii) only (c) (i) and (ii) (d) (iii) and (iv) 34. Teacher asked three students to write one precaution by each of them regarding the experiment on tracing the path of light ray through glass slab. First, second and third student wrote down following precautions, respectively. (i) While tracing emergent rays, we should see heads of pins. (ii) One eye should be kept closed, while tracing emergent ray. (iii) Glass slab should have parallel edges. The correct statements are of (a) 1 and 2 (b) 2 and 3 (c) 1 and 3 (d) All three. 35. Which of the following do you think will give the maximum foam (a) Aquaguard water (b) Distilled Water (c) Water from the River (d) Sea Water 36. For determining the focal length of a concave mirror by obtaining sharp and distinct image of a distant object, out of the following options a student should prefer as object. (a) a burning candle kept at the distant edge of the laboratory table. 247 [Class-X – Science] (b) well-lit grill of the laboratory window. (c) a well-lit distant building. (d) a distant tree. 37. The correct labelling for part A, B and C is A C (a) A - Cotyledon B - radicle C - plumule (b) A - leaf B - shoot C - root (c) A - leaf B - embryo C - cotyledon (d) A - cotyledon B - plumule C - radicle 38. A student prepared 20% sodium hydroxide solution in a beaker containing water. The observation noted by him are given below: (I) Sodium hydroxide is in the form of pellets. (II) It dissolves in water readily. (III) The beaker appears cold when truched from outside. (IV) The red litmus paper turns blue when dipped into the solution. The correct observation are: (a) I, II and III (b) II, III and IV (c) III, IV and I (d) I, II and IV 39. For tracing the path of a ray of light through a glass prism, the most appropriate distance between the two pins must be [Class-X – Science] 248 (a) 11 to 13cm. (b) 7 to 10cm. (c) 3 to 5cm. (d) 2 to 4cm. 40. A student adds sodium hydroxide to given vegetable oil for preparation of soap. Here, sodium hydroxide is used for (a) neutralisation of vegetable oil (b) hydrolysis of vegetable oil (c) oxidation of vegetable oil (d) dehydration of vegetable oil. 41. Four students showed the following traces of the path of a ray of light passing through a rectangle glass slab. (I) (II) (III) (IV) The trace must likely to be correct is that of student (a) I (b) II (c) III (d) IV 42. On adding 2 ml. acetic acid to 2 ml. of water in a test tube, it was observed that : (a) a clear and transparent solution is formed. (b) a white precipitate is formed almost immediately. (c) two separate layers were formed. (d) a colourless and odourless gas is evolved. 249 [Class-X – Science] (UNSOLVED) SAMPLE PAPER-II Time : 3 hrs. Max. Marks = 90 CLASS X 1. State one function of Iris in human eye. 1 2. Saturated hydrocarbons burn with a blue flame while unsaturated hydrocarbon burn with a sooty flame. Why? 1 3. Name the type of asexual reproduction in Hydra and Planaria? 1 4. What is the cause of dispersion of white light passing through a prism? Which colour of light deviates the (i) must, (ii) least. 2 5. Why does the clear sky appear blue? How would the sky appear in the absence of earth’s atmosphere? 2 6. What is ozone and how does it affect an ecosystem? 2 7. Differentiate between self and cross pollination? 2 8. A needle placed 45cm. from a lens forms an image on a screen placed 90 cm. on the other side of the lens. Identify the type of lens. Determine its focal length and the power. What is the size of image of needle is 5cm. in height? 9.(a) For the same angle of incidence 45°, the angle of refraction in two transparent media I and II is 20° and 30° respectively. Out of I and II which medium is optically denser and why? 3 (b) Light enters from air to diamond which has refractive index of 2.42. Calculate the speed of light in diamond if speed of light in air is 3×108m/s. [Class-X – Science] 250 10. Explain why? 3 (i) Danger signals are red in colour. (ii) Convex mirrors are commonly used as rear view mirrors. 11. What is meant by homologous series of organic compounds? Write the chemical formulae of two members of a homologous series and state which part determines (i) physical properties, (ii) chemical properties of there compounds. 3 12. What is ten percent law? Explain with an example how energy flows through different trophic levels? 3 13. If we cross pure-bred tall (dominant) pea plant with pure-bred dwarf (recessive) pea plant we will get pea plants of F1 generation. If we now self-cross the pea plant of F1 generation, then we obtain pea plants of F2 generation. 3 (a) What do the plants of F1 generation look like? (b) State the ratio of tall plants to dwarf plants in F2 generation. (c) State the type of plants not found in F1 generation but appeared in F2 generation, mentioning the reason for the same. 14.(a) Name an element you would expect to show chemical reactions similar to sodium. State the reason in support of your answer. (b) Write electronic configuration of the element belonging to 3rd period and 13th group of periodic table. Predict whether it is a metal or a nonmetal. Give reason. 15. With the help of ray diagrams in case of a convex lens, show the formation of : 3 (a) Virtual and erect image (b) real, inverted and magnified image. (c) real, inverted and diminished image. 16. Why should we conserve forests? Suggest any two ways to conserve forests? 3 251 [Class-X – Science] 17. Distinguish between bio-degradable and non-biodegradable substances. List two effects of each of them on the environment. 18. Explain how equal genetic contribution of male and female parents is ensured in the progeny. 3 19.(a) What are small numbers of surviving tigers a cause of worry from the point of view of genetics? 3 (b) What is meant by the term Gene Flow? 20. A quiz contest was being held in the school for chemistry students. The quiz master said: 5 An element has the electronic configuration 2, 8, 7 (a) What is the atomic number of this element? (b) Which of the elements N, F, P and Ar shows similarily with this element? (c) We daily use a compound of this element in our food. What is that? (d) A compound of this element causes hardness of water. What is that? Rohit replied to all these questions correctly. Can you reproduce his answers? 21.(i) What is Genetics? 5 (ii) Give common name of the plant on which Mendel performed his experiments? (iii) What for did Mendel used the term factor and what are these factors called now? (iv) What are Genes? Where are the genes located? 22.(a) Explain. The role of placenta in the development of human embryo.5 (b) Give example of two bacterial and two viral sexually transmitted diseases. Name the most effective contraceptive which prevents spread of such diseases. [Class-X – Science] 252 23.(a) Define the term ‘Isomers’. 5 (b) Draw two possible isomers of the compound with molecular formula C3H6O and write their names. (c) Give the electron dot structures of the above two compounds. 24.(a) State the laws of refraction of light. Give an expression to relate the absolute refractive index of a medium with speed of light in vacuum. (b) The refractive indices of water and glass with respect to air are 4/3 and 3/2 respectively. If the speed of light in glass is 2 × 108 m/s. Find the speed of light in (i) Air and (ii) Water.. 25. A student recorded the following sets of observations during the experiment of tracing the path of a ray of light passing through a glass slab. S.No. I II III IV i 30° 40° 50° 60° r 19° 27° 37° 35° e 30° 40° 51° 59° The incorrect observation is at serial number (a) I (b) II (c) III (d) IV 26. In the experiment on tracing the path of a ray of light through a glass slab, four students A. B, C and D used the following values of angle of incidence and the distance between the two pins (fixed on the line representing the incident ray) (A) (30°, 45°, 60°) and 2cm. (B) (30°, 45°, 60°) and 8cm. 253 [Class-X – Science] (C) (20°, 50°, 70°) and 8cm. (D) (20°, 50°, 70°) and 8cm. Out of these the best choice is that of student (a) A (b) B (c) C (d) D 27. A student obtains a blurred image of an illuminated distant tower on a screen by using a convex lens. In order to obtain sharp image of tower on the screen, he must shift the lens. (a) Towards the screen (b) away from the screen (c) to a position very far away from the screen (d) either towards or away from the screen depending upon the position of tower. 28. Salman has to perform the experiment of finding the focal length of a given concave mirror by using a distant object. Which of the following set ups will he choose apart from the mirror and screen provided. (a) a mirror holder and a scale (b) a mirror holder, a screen holder and a scale. (c) a screen holder and a scale. (d) a mirror holder and a screen holder. 29. Select from the following the best set-up for tracing the path of a ray of light through a rectangular glass slab: (I) [Class-X – Science] (II) (III) 254 (IV) (a) I (b) II (c) III (d) IV 30. A sharp image of a distant object is obtained on a screen using a convex lens. In order to determine the focal length of lens, we need to measure the distance between (a) object and the lens (b) object and its image (screen) (c) lens and the image (screen) (d) lens and the screen and also object and the screen. 31. For the refraction of a ray of light through a glass prism, the path of a ray of light is shown below: Z X M Y N The angle of incidence, the angle of emergence and the angle of deviation respectively have been represented by (a) Y, N, Z (b) X, Z, M (c) X, N, Z (d) X, M, Z 32. When soap is added to hard water, we observe that (a) Soap does not react (b) Soap disappears immediately (c) A scum is formed which floats on the surface of water (d) None of above happens. 255 [Class-X – Science] 33. When ethanoic acid is added to a solution of substance X, a colourless and colourless gas Y is liberated. The gas Y burns lime water milky. The substance X is (a) Sodium carbonate (b) Sodium hydroxide (c) Sodium acetate (d) Lime water. 34. 15 ml. each of ethanoic acid and water are mixed together and shaken in a test tube as given below: Ethanoic acid Water Clear Solution Ethanoic acid Water (I) Turbo solution (II) (III) (IV) The resulting mixture after standing would appear as shown in test tube (a) I (b) II (c) III (d) IV 35. Castor oil was taken in a test tube and agitated alongwith aqueous sodium hydronide solution but there was a difficulty in precipitating the soap. Then a substance X was added and after sometime, complete precipitation of soap was achieved. The substance X is (a) Oxalic acid (b) Citric acid (c) Sodium chloride (d) Depends upon the oil 36. Correct definition of homologous organs is (a) different functions, same origin (b) same function, different origin (c) same or different function, but similar origin [Class-X – Science] 256 (d) same or different function, but different origin. 37. A student has to observe a permanent slide of binary fission in amoeba. Find the correct sequence of steps given below for focussing the object under a microscope. (i) Place the slide on the stage, look through the eye-piece and adjust the mirror to get proper illumination. (ii) Focus the slide sharp using fine adjustment screw. (iii) Look through the eye-piece and raise the objective lens using coarse adjustment screw till the object is focussed. (iv) Look through the eye-piece and none the slide till the object is visible. (a) (iv), (iii), (ii), (i) (b) (i), (ii), (iv), (iii) (c) (i), (iv), (iii), (ii) (d) (i), (iii), (iv), (ii) 38. Which organ of the embryo in dicot seeds generally stores the food (a) Radicle (b) Colyledons (c) Plumule (d) Endosperms 39. Following diagram depicts the stages of budding yeast. The correct sequence is (i) (ii) (iii) 257 (iv) [Class-X – Science] (a) 1, 2, 3, 4 (b) 1, 3, 4, 2 (c) 1, 4, 2, 3 (d) 3, 2, 1, 2 40. Dilute acetic acid was added to four beakers containing following chemicals: (I) NaCl (II) (III) KOH (IV) NaHCO3 K2CO3 Brisk effervescence and evolution of colourless gas was observed in the beakers (a) I and II (b) II and III (c) III and IV (d) II and IV 41. A student while performing experiment to observe embryo of dicot seed saw that the seed kept submerged in a beaker full of water and kept in light failed to germinate. The possible reason for it can be (a) Seeds did not get oxygen (b) The seeds were kept in light (c) The seeds were not viable (d) Both (a) and (c) 42. Which group out of the following represents homologous organs? (a) Potato, ginger, sweet potato (b) Turnip, reddish, carrot (c) Carrot, sweet potato, potato (d) Ginger, potato, carrot. [Class-X – Science] 258 (UNSOLVED) SAMPLE PAPER-III Time : 3 hrs. Max. Marks = 90 CLASS X 1. State modern periodic law 1 2. Which mirror is used by dentists? 1 3. What is the full form of CFC? 1 4. Why are unsaturated hydrocarbons more reactive than saturated ones?2 5. Differentiate between self pollination and cross pollination. 2 6. Why should the fossil fuels be used judiciously? 2 7. Although coal and petroleum are produced by degradation of biomass, yet we need to conserve them. Why? 2 8. Draw the e¯dot structures of ethane, ethene and ethyne. 3 9. Explain why sodium is more reactive than Lithium. 3 10. Two elements X (at no. 11) and Y (at no. 13) are placed in the III Period of the modern periodic table. 3 (i) Which amongst the two has more metallic character? (ii) Calculate the valency of each element. (iii) Element Y is smaller than X in terms of atomic size. Is the statement true? Justify. 11. Draw a labelled diagram of the longitudinal section of flower. 259 3 [Class-X – Science] 12. Describe STD’s and mention the way to prevent them. 3 13. Explain acquired and inherited traits. 3 14. Do genetic combination of mothers play a significant role in determining the sex of a new born? Explain. 3 15. Why do we prefer a convex mirror as a rear-view mirror in vehicles?3 16. Find the focal length of a convex mirror whose radius of curvature is 32 cm. 3 17. Find the focal length of a lens of power-2.0D. What type of lens is this? 3 18. Why are stars seen higher in the sky than they actually are? 3 19. What is ozone and how does it affect any ecosystem? 3 20. Explain the mechanism of the cleansing action of soaps. 5 21. Draw a human female reproductive system and label its 4 parts. 5 22. In a cross between Tall and Dwarf plant, the F1 generation had all Tall plants. When the F1 generation was self crossed, it was observed that in the F2 generation, out of 100, 75 plants were Tall and the rest were dwarf. Make a cross and answer the following:5 (a) What is the genotype of F1 progeny? (b) What is the ratio of Tall and Dwarf plants in the F2 generation? 23. Explain refraction. Draw a ray diagram indicating the changes in the path of light (in a glass slab) till it emerges out. 5 24. An object 5cm high is kept 25cm away from a converging lens (convex) of focal length 10cm. What is the nature, position and the size of the image? 5 25. An aqueous solution of acetic acid [Class-X – Science] 260 (a) turns wet blue litmus paper red (b) turns dry blue litmus paper red (c) turns both dry and wet blue litmus paper red (d) will not turn both papers red. 26. The odour of acetic acid is similar to that of (a) ethanol (b) sulphur (c) vinegar (d) lemon. 27. Which of the following is hard water? (a) Rain water (b) Distilled water (c) Sea water (d) Filtered water 28. The diagram illustrates:(a) Binary fission in amoeba (b) Bud formation in amoeba (c) Binary fission in hydra (d) Bud formation in hydra. 29. First leaves of the dicot plants are formed from (a) radicle (b) cotyledons (c) seed coat (d) roots 30. Which of the following statements about soaps is not true? (a) They are sodium salts of long chain fatty acids (b) Soaps act as cleaning agents (c) They are produced by the hydrolysis of fats and oils (d) The exact composition of soap is dependent on the fat or oils from which it is formed. 261 [Class-X – Science] 31. Homology and analogy are helpful in studying and interpreting (a) commercial uses of structures (b) evolutionary relationship (c) functional relationship structural relationship (d) 32. Which diagram(s) is/are correct (of a dicot seed) (I) (II) (III) (a) Only I (b) Both II & III (c) Only IV (d) All are correct. (IV) 33. Which of the following diagram is correct? P Q P (a) Q (b) R R S S P P Q Q H (c) (d) R R S S 34. No matter how far an object is from the spherical mirror, the image of the object appears erect. The mirror is (a) Concave (b) Plane (c) Convex (d) None of the above [Class-X – Science] 262 35. In order to get real and inverted image of the same size formed by a convex lens, the object should be placed (a) at F (b) at infinity (c) at 2F (d) between optical centre and F 36. The deviation produced by a prism is (a) same for all wavelengths (b) greatest for red and least for violet (c) greatest for violet and least for red (d) the prism produces no deviation 37. When an object is placed in front of a convex lens, the image formed (a) is always erect (b) is always real (c) is always inverted (d) may be real or virtual 38. A lens is held 3cm above the printed letters of a book. It is observed that the printed letter appear bigger. The type of lens is (a) double convex lens (b) glass (c) concave lens (d) none of the above. (a) skin folds (b) hindlimbs (c) forelimbs (d) skin out growths. 39. Wings of a bird are modified 40. Monocots and dicots belong to (a) Angiosperms (b) Gymnosperms (c) Bryophyta (d) Pteridophyta 41. 5ml of acetic acid was added to equal volume of water and the mixture was shaken for one minute and allowed to settle. The correct representation of the observations made would be as given in test tube. 263 [Class-X – Science] Acid Water Acid Water Acid Clear Solution water Water Acid Water (i) (ii) (iii) (iv) 42. The temporary hardness of water is due to (a) Calcium bicarbonate (b) Calcium carbonate (c) Calcium chloride Calcium sulphate [Class-X – Science] (d) 264 SCIENCE CBSE : 2013-14 Time : 3 hrs. Max. Marks = 90 CLASS X 1. Write the no. of vertical columns in the modern periodic table. What are these columns called? 2. Give the respective scientific terms used for studying. (i) the mechanism by which variations are created and inheritedand (ii) the development of new type of organisms from the existing ones. 3. Water is a valuable resource. List two ways that you would suggest every family member to save this resource. 4. List four advantages of vegetative propagation. 5. Draw a ray diagram to show the path of the reflected ray corresponding to an incident ray which is directed towards the principal focus of a convex mirror. Mark on it the angle of incidence and the angle of reflection. 6. Why is Government of India imposing a ban on the use of polythene bags? Suggest two alternatives to these bags and explain how this ban is likely to improve the environment. 7. What is meant by bio-diversity? List two advantages of conserving forest and wild-life. 265 [Class-X – Science] 8. State the meaning of functional group in a carbon compound. Write the functional group present in (i) Ethanol and (ii) Ethanoic acid and also draw their structures. 9. Write the name and general formula of a chain of hydro carbons in which an addition reaction with hydrogen can take place. Stating the essential conditions required for an addition reaction to occur write the chemical equation giving the name of the reactant and the product of such a reaction. 10. Based on the group valency of elements state the formula for the following giving justification for each: (i) Oxides of 1st group elements (ii) Halides of the elements of group 13 and (iii) Compounds formed when an element of group 2 combines with an element of group 16. 11.(a) Define the following terms: (i) Valency (ii) Atomic size. (b) How do the valency and the atomic size of the elements vary while going from left to right along a period in the modern periodic table? 12. Draw diagrams to explain the regeneration that takes place in each of the body parts of planaria when its body is cut into three pieces. Name any other organism in which a similar process can be observed. 13. List any four methods of contraception used by humans. How does their use have a direct effect on the health and prosperity of a family? 14.(a) Give the evidence that the birds have evolved from reptiles. (b) Insects, octopus, planaria and vertebrates possess eyes. Can we group these animals together on the basis of eyes that they possess? Justify your answer giving reason. 15. A cross was made between pure breeding pea plants, one with round and green seeds and the other with wrinkled and yellow seeds. [Class-X – Science] 266 (a) Write the phenotype of F1 progeny. Give reason for your answer. (b) Write the different types of F2 progeny obtained along with their ratio when F1 progeny was selfed. 16. A spherical mirror produces an image of magnification -1 on a screen placed at a distance of 50cm from the mirror. (a) Write the type of mirror (b) Find the distance of the image from the object (c) What is the focal length of the mirror (d) Draw the ray diagram to show the image formation in this case. 17. State the laws of refraction of light. If the speed of light is vaccum is 3×108ms-1, find the speed of light in a medium of absolute refractive index 1.5. 18. Explain giving reason why the sky appears blue to an observer from the surface of the earth? What will the colour of the sky be for an astronaut staying is the international space station arbiting the earth? Justify your answer giving reason. 19. “Our food grains such as wheat and rice, the vegetables and fruits and even meat are found to contain varying amounts of pesticide residues.” State the reason to explain how and why it happens? 20. State the reason why carbon can neither form C4+ cations nor C4avions, but forms covalent compounds. Also state reasons to explain why covalent compounds: (i) bad conductors of electricity? (ii) have low melting and boiling points? 21.(a) Give one example each of a unisexual and a bisexual flower. (b) Mention the changes a flower undergoes after fertilisation. (c) How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals? 267 [Class-X – Science] 22. Name the respective part of human female (a) Reproductive System: (i) that produces eggs (ii) where fusion of egg and sperm takes place and (iii) where zygote gets implanted. (b) Describe in brief what happens to the zygote after it gets implanted. 23. A student wants to project the image of a candle flame on the walls of school laboratory by using a lens: (a) which type of lens should be use and why? (b) At what distance in terms of focal length ‘f’ of the lens should be place the candle flame so as to get (i) a magnified and (ii) a diminished image respectively on the wall? (c) Draw ray diagram to show the formation of the image in each case. 24.(a) List three common refractive defects of vision. Suggest the way of correcting these defects. (b) About 45 lacs people in the developing countries are suffering from comeal blindness. About 30 lacs children below the age of 12 years suffering from this defect can be cured by replacing the defective cornea with the cornea of a donated eye. How and why can students of yourage involve themselves to create awareness about this fact among people? 25. When you add about 2ml of acetic acid to a test tube containing an equal amount of distilled water and leave the test tube to settle after shaking its contents, then after about 5 minutes what will you observe [Class-X – Science] 268 in the test tube: (a) A white precipitate setting at its bottom (b) A layer of water over the layer of acetic acid or (c) A layer of acetic acid over the layer of water. 26. A student adds a few drops of ethanoic acid to test tubes X, Y and Z containing aqueous solutions of NaCl, NaoH and Na2CO3 respectively. If he now brings a burning splinter near the mouth of the test tubes immediately after adding the ethanoic acid in each one of them, in which of the test tube or test tubes the flame gets extinguished? (a) X and Y (b) Y and Z (c) X and Z (d) only Z. 27. In order to study saponification reaction the first prepare 20% solution of NaoH. If we record the temperature of this solution just after adding NaoH flakes to water and also test its nature using litmus, it may be concluded that the process of making this solution is: (a) Exothermic and the solution is alkaline (b) Endothermic and the solution is alkaline (c) Endothermic and the solution is acidic (d) Exothermic and the solution is acidic. 28. While studying saponification reaction for the preparation of soap, the teacher suggested to a student to add a small quantity of common salt to the reaction mixture. The function of common salt in this reaction is to: (a) Reduce the alkalinity of the soap (b) Reduce the acidity of the soap (c) Enhance the cleansing capacity of soap or (d) Favour precipitation of soap. 269 [Class-X – Science] 29. A student takes about 6ml of distilled water in each of the four test tubes P, Q, R and S then dissolves an equal amount of four different salts namely sodium chloride in ‘P’, potassium chloride in ‘Q’ , calcium chloride in ‘R’ and magnesium chloride in ‘S’. He then adds 10 drops of soap solution to each test tube and shake its contents. The test tube in which sum (insoluble substance) is formed with soap are: (a) P and Q (b) Q and R (c) R and S (d) Q and S. 30. A student has obtained the image of a distant object with a concave mirror to determine its focal length. If he has selected a well illuminated red building as object, which of the following correctly describes the features of the image formed? (a) Virtual, inverted, diminished image in red shade. (b) Real erect, diminished image in pink shade. (c) Real, inverted, diminished image in red shade. (d) Virtual, erect, enlarged image in red shape. 31. A student has obtained an image of a distant object on a screen to determine the focal length F1 of the given lens. His teacher after checking the image, gave him another lens of focal length F2 and asked to focus the same object on the same screen. The student found that to obtain a sharp image he has to more the lens away from the screen. From this finding we may conclude that both the lenses given to the student were: (a) Concave and F1<F2 (b) Convex and F1<F2 (c) Convex and F1>F2 (d) Concave and F1>F2 32. Study the following four experimental set-ups I, II, III and IV for the experiment, “To trace the patch of a ray of light through a rectangular glass slab.” Which of the marked set-ups is likely to give best results (F1 & F2 are the positions of pins fixed on the incident ray)? [Class-X – Science] 270 P1 P1 P2 (I) P1 P1 P2 P2 P2 (IV) (III) (II) (a) I (b) II (c) III (d) IV 33. On the basis of their experiment, “To trace the path of a ray of light through a rectangular glass slab,” students of a class arrived at which one of the following conclusions: (a) Angle of incidence is greater than the angle of emergence, (b) Angle of emergence is smaller than the angle of refraction, (c) Emergent ray is parallel to the refracted ray, (d) Incident ray and emergent ray are parallel to each other. 34. The path of a ray of light passing through a glass prism is shown below: O Z X M Y N In this diagram the angle of prism, angle of incidence, angle of emergence and angle of deviation respectively have been representedby: (a) O, Y, Z and N (b) P, Y, M and Z (c) O, X, M and Z (d) P, X, Z and N. 271 [Class-X – Science] 35. A student is observing the diagram showing the path of a ray of light passing through a glass prism. He would find for all angles of incidence the ray of light bends: (a) towards the normal while entering into the prism and away from the normal while emerging out of the prism, (b) away from the normal while entering into the prism and towards the normal while emerging out of the prism, (c) away from the normal while entering as well as while emerging out of the prism, (d) towards the normal while entering as well as while emerging out of the prism. 36. A student was asked by his teacher to find the image distance for various object distances in case of a given convex lens. He performed the experiment with all precautions and noted down his observations in the following table: S. No. 1. 2. 3. 4. 5. 6. Object Distance (cm) 60 48 36 24 18 16 Image Distance (cm) 15 16 21 24 36 48 After checking the observation table the teacher pointed out that there is a mistake in recording the image distance in one of the observations. Find the serial number of the observation having faulty image distance. (a) 2 (b) 3 (c) 5 (d) 6 37. A student has obtained a magnified image of a flame on a screen using a convex lens. To draw the corresponding ray diagram, to show the image formation, which of the following two rays whose paths after refraction are shown he should select? [Class-X – Science] 272 O (I) (II) O O F (III) f (IV) (a) I and II (b) II and III (c) III and IV (d) I and III 38. Study the following diagrams showing various stages of binary fission in Amoeba: (I) (II) (III) (IV) The correct sequence of these diagrams should be: (a) I, IV, II, II, V (b) I, III, IV, II, V (c) I, II, IV, III, V (d) I, II, III, IV, V 39. Identify the figures showing the process of budding in yeast. (I) (III) (II) 273 (IV) [Class-X – Science] (a) I, II and III (b) II, III and IV (c) I, II and IV (d) III, IV and I 40. Which one of the following pairs of vegetables is an example of homologues structures: (a) Potato & Sweet Potato (b) Carrot and Radish (c) Carrot and Tomato (d) Tomato and Radish 41. Four students P, Q, R and S differently reported the following set of organs to be analogus: P- Forelimb of frog and forelimb of a lizard. Q- Forelimb of bird and forelimb of a human. R- Wings of a parrot and wings of a butterfly. S- Wings of a bird and wings of bat. The two students who have reported correctly are” (a) P and Q (b) Q and R (c) R and S (d) P and S 42. You are asked by your teacher to study the different parts of an embryo of a gram seed. Given below are the steps to be followed for the experiment: (i) Soak the gram seeds in plain water and keep them overnight (ii) Cut open the soaked seed and observe its different parts (iii) Take some dry gram seeds in a petri dish (iv) Drain the excess water (v) Cover the soaked seeds with a wet cotton cloth and leave than for a day. The correct sequence of these steps is: (a) III, I, V, IV, II (b) III, I, II, IV, V (c) III, IV, V, I, II (d) III, I, IV, V, II [Class-X – Science] 274 SCIENCE CBSE : 2013-14 Time : 3 hrs. Max. Marks = 90 CLASS X 1. Write the number of horizontal rows in the modern periodic table. What are these rows called? 2. Name the information source for making proteins in the cells. 3. List two measures that you would suggest for the better management of water resources. 4. List four modes of asexual reproduction. 5. Draw a ray diagram to show the path of the reflected ray corresponding to an incident ray which is directed parallel to the principal axis of a convex mirror. Mark on it the angle of incidence and the angle of reflection. 6. In some states of our country there is a ban on the use of polythene bags for shopping why? List three advantages of using jute or cloth bags over polythene bags. 7. List three problems which arise due to construction of big dams. Suggest a solution of these problems. 8. Our food grains such as wheat and rice, the vegetables and fruits and even meat are found to contain varying amounts of pesticide residues. State the reason to explain how and why it happens. 275 [Class-X – Science] 9. List any four methods of contraception used by humans. How does their use have a direct effect on the health and prosperity of a family? 10. (a) Write the names of these parts of a flower which serve the same function as the following do in the animals : (i) testis (ii) sperm (iii) ovary (iv) egg. (b) State the function of flowers in the flowering plants. 11. (a) Give the evidence that the birds have evolved from reptiles. (b) Insects, octopus, planaria and vertebrates posses eyes. Can we group these animals together on the basis of eyes that they possess? Justify your answer giving reason. 12 (a) Mendel crossed tall pea plants with dwarf pea plants in his experiment. Write his observations giving reasons on the F1 and F2 generations. (b) List any two contrasting characters other than height that Mendel used in his experiments in pea plants. 13. State the lanes of refraction of light. If the speed of light in vacuum is 3×108ms-1, find the speed of light in a medium of absolute refractive index 1.5. 14. A spherical mirror produces an image of magnification -1 on a screen placed at a distance of 40 cm from the mirror. (i) Write the type of mirror. (ii) What is the nature of the image formed? (iii) How far is the object located from the mirror? (iv) Draw the ray diagram to show the image formation in this case. 15. Why does the sun seem to rise two minutes before the actual sunrise and set two minutes after the actual sunset? Explain with the help of labelled diagram. [Class-X – Science] 276 16. Write the name and general formula of a chain of hydrocarbons in which an addition reaction with hydrogen can take place. Stating the essential conditions required for an addition reaction to occur write the chemical equation giving the name of the reactant and the product of such a reaction. 17. State the meaning of the functional group in an organic compound. Write the formula of the functional group present in alcohols, aldehydes, ketones and carboxylic acids. 18. (a) Define the following terms : (i) Valency (ii) Atomic size. (b) How do the valency and the atomic size of the elements vary while going from left to right along a period in the modern periodic table? 19. Consider two elements ‘A’ (Atomic number 17) and ‘B’ (Atomic No.19) (i) Write the positions of these elements in the modern periodic table giving justification. (ii) Write the formula of a compound formed when ‘A’ combines with ‘B’. (iii) Draw the electron dot structure of the compound and state the nature of the bond formed between the two elements. 20. State the reason why carbon can neither form C4+ cations nor C4anions, but forms covalent compounds. Also state reasons to explain why covalent compounds: (i) are bad conductors of electricity? (ii) have low melting and boiling points. 21(a) Name the respective part of human female reproductive system: (i) that produces eggs (ii) where fusion of egg and sperm takes place and (iii) where zygote gets implanted 277 [Class-X – Science] (b) Describe in brief what happens to the zygote after it gets implanted. 22(a) Give one example each of a unisexual and a bisexual flower. (b) Mention the changes a flower undergoes after fertilization. (c) How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals. 23(a) List these common refractive defects of vision. Suggest the way of correcting these defects. (b) About 45 lac people in the developing countries are suffering from corneal blindness. About 30 lacs children below the age of 12 years suffering from the defect can be cured by replacing the defective cornea with the cornea of a donated eye. How and why can students of your age involve themselves to create awareness about this fact among people? 24. A student wants to project the image of a candle flame on the walls of school laboratory by using a mirror. (a) Which type of mirror should be use and why? (b) At what distance in terms of focal length ‘f’ of the mirror should be place the candle flame so as to get the magnified image on the wall? (c) Draw a ray diagram to show the formation of image in this case. (d) Can he use the mirror to project a diminished image of the candle flame on the same wall? State ‘how’ if your answer is ‘yes’ and ‘why not’ if your answer is ‘no’. 25. A student has obtained an image of a distant object on a screen to determine the focal length F1 of the given lens. His teacher after checking the image, gave him another lens of focal length F2 and asked to focus the same object on the same screen. The student found that to obtain a sharp image he has to move the lens away from the screen. From this finding we may conclude that both the lenses given to the student were: [Class-X – Science] 278 (a) C o n cav e an d F 1<F2 (c) Convex and F1<F2 (b) Convex and F1<F2 (d) Concave and F1<F2 26. A student has obtained the image of a distant object with a concave mirror to determine its focal length. If he has selected a well illuminated red building as object, which of the following correctly describes the features of the image formed? (a) Virtual, inverted, diminished image in red shade (b) Real, erect, diminished image in pink shade (c) Real, inverted, diminished image in red shade (d) Virtual, erect, enlarged image in red shade 27. A student has obtained a magnified image of a flame on a screen using a convex lens. To draw the corresponding ray diagram, to show the image formation, which of the following two rays whose paths after refractions are shown he should select? O (I) (II) O O F (III) F (IV) (a) I and II (b) II and III (c) III and IV (d) I and III 279 [Class-X – Science] 28. A student was asked by his teacher to find the image distance from various object distances in case of a given convex lens. He performed the experiment with all precautions and noted down his observations in the following table: S. No. Object distance (cm) Image distance (cm) 1 60 15 2 48 16 3 36 21 4 24 24 5 18 36 6 16 48 After checking the observation table the teacher pointed out that there is a mistake in recording the image distance in one of the observations. Find the serial number of the observation having faulty image distance. (a) 2 (b) 3 (c) 5 (d) 6 29. A student is observing the diagram showing the path of a ray of light passing through a glass prism. He would find that for all angles of incidence the ray of light bends: (a) towards the normal while entering into the prism and away from the normal while emerging out of the prism. (b) away from the normal while entering into the prism and towards the normal while emerging out of the prism. (c) away from the normal while entering as well as while emerging out of the prism. (d) towards the normal while entering as well as while emerging out of the prism. 30. The path of a ray of light passing through a glass prism is shown below: [Class-X – Science] 280 O Z X M Y N In this diagram the angle of prism, angle of incidence, angle of emergence and angle of deviation respectively have been representedby: (a) O, Y, Z and N (b) P, Y, M and Z (c) O, X, M and Z (b) P, X, Z and N 31. On the basis of their experiment, “To trace the path of a ray of light through a rectangular glass slab,” students of a class arrived at which one of the following conclusions : (a) Angle of incidence is greater than the angle of emergence, (b) Angle of emergence is smaller than the angle of refraction, (c) Emergent ray is parallel to the refracted ray, (d) Incident ray and emergent ray are parallel to each other. 32. Study the following four experimental set-ups, I, II, III and IV for the experiment, “To trace the path of a ray of light through a rectangular glass slab.” P1 P1 P2 (I) P1 P1 P2 P2 P2 (III) (II) (IV) Which of the marked set-ups is likely to give best results (P1 and P2 are the positions of pins fixed on the incident ray)? (a) I (b) II (c) III (d) IV 281 [Class-X – Science] 33. You are asked by your teacher to study the different parts of an embryo of a gram seed. Given below are the steps to be followed for the experiment: I. Soak the gram seeds in plain water and keep them overnight. II. Cut open the soaked seed and observed its different parts. III. Take some dry gram seeds in a petri dish. IV. Drain the excess water. V. Cover the soaked seeds with a wet cotton cloth and leave them for a day. The correct sequence of these steps is : (a) III, I, V, IV, II (b) III, I, II, IV, V (c) III, IV, V, I, II (d) III, I, IV, V, II 34. Four students P, Q, R and S differently reported the following set of organs to be analogous : P. Forelimb of a frog and forelimb of a lizard Q. Forelimb of a bird and forelimb of a human R. Wings of a parrot and wings of a butterfly S. Wings of a bird and wings of a bat. The two students who have reported correctly are : (a) P and Q (b) Q and R (c) R and S (d) P and S 35. Which one of the following pairs of vegetable is an example of homologous structures : (a) Potato & sweet potato(b) Carrot and radish (c) Carrot and tomato [Class-X – Science] (d) Tomato and radish 282 36. Identify the figures showing the process of budding in yeast. (I) (III) (II) (a) I, II and III (b) II, III and IV (c) I, II and IV (d) III, IV and I (IV) 37. Study the following diagrams showing various stages of binary fission in Amoeba : (I) (II) (III) (IV) (a) I, IV, III, II, V (b) I, III, IV, II, V (c) I, II, IV, III, V (d) I, II, III, IV, V 38. A student takes about 6 ml of distilled water in each of the four test tubes P, Q, R and S, then dissolves an equal amount of four different salts namely sodium chloride in ‘P’, potassium chloride in ‘Q’, calcium chloride in ‘R’ each test tube and shakes its contents. The test tubes in which scum (insoluble substance) is formed with soap are: (a) P and Q (b) Q and R (c) R and S (d) Q and S 39. A student adds a few drops of ethanoic acid to test tubes X, Y and Z containing aqueous solutions of sodium chloride, sodium hydroxide and sodium carbonate respectively. If he now brings a burning splinter near the mouth of the test tubes immediately after adding the ethanoic acid in each one of them, in which of the test tube or test tubes the flame gets extinguished? 283 [Class-X – Science] (a) X and Y (b) Y and Z (c) X and Z (d) only Z 40. When you add 2 mL of acetic acid to a test tube containing an equal amount of distilled water and leave the test tube to settle after shaking its contents, then after about 5 minutes what will you observe in the test tube : (a) A white precipitate settling at its bottom. (b) A clear colourless solution. (c) A layer of water over the layer of acetic acid, or (d) A layer of acetic acid over the layer of water. 41. In order to study saponification reaction we first prepare 20% solution of sodium hydroxide. If we record the temperature of this solution just after adding sodium hydroxide flakes to water and also test its nature using litmus, it may be concluded that the process of making this solution is : (a) exothermic and the solution is alkaline. (b) endothermic and the solution is alkaline. (c) endothermic and the solution is acidic. (d) exothermic and the solution is acidic. 42. While studying saponification reaction for the preparation of soap, the teacher suggested to a student to add a small quantity of common salt to the reaction mixture. The function of common salt in this reaction is: (a) reduce the alkalinity of the soap, (b) reduce the acidity of the soap, (c) enhance the cleansing capacity of soap, or (d) favour precipitation of soap. [Class-X – Science] 284 SCIENCE CBSE : 2013-14 Time : 3 hrs. Max. Marks = 90 CLASS X 1. Write any one difference in the electronic configurations of group-I and group-2 elements? 2. Write the contribution of Charles Darwin in the field of ‘evolution’. 3. “We need to manage our resources”. List two reasons to justify this statement. 4. List four modes of asexual reproduction other than fission in the living organisms. 5. Draw a ray diagram to show the path of the reflected ray corresponding to an incident ray of light parallel to the principal axis of a concave mirror. Mark the angle of incidence and angle of reflection on it. 6. List two environment friendly practices of habits which need to be followed by every member of a family/community. Explain how these practices will support the ‘save the environment’ mission. 7. ‘Affluent life style has a negative effect on the environment’. Justify this statement with the help of an example. 8. “Our food grains such as wheat and rice, the vegetables and fruit and even meat are found to contain varying amounts of pesticides residues.” State the reason to explain how and why it happens. 285 [Class-X – Science] 9. State the laws of refraction of light. If the speed of light in vacuum is 3×108ms-1, find the speed of light in a medium of absolute refractive index is 1.5. 10. A spherical mirror produces an image of magnification –1.0 on a screen placed at a distance of 30 cm from the pole of the mirror. (i) Write the type of mirror in this case. (ii) What is the focal length of the mirror? (iii) What is the nature of the image formed? (IV) Draw the ray diagram to show the image formation to this case. 11. What are esters? How are they prepared? List two uses of esters. 12. Write the name and general formula of a chain of hydrocarbons in which an addition reaction with hydrogen can take place. Stating the essential conditions required for an addition reaction to occur write the chemical equation giving the name of the reactant and the product of such a reaction. 13(a) Define the following terms (i) Valency (ii) Atomic size (b) How do the valency and the atomic size of the elements vary while going from left to right along a period in the modern periodic table? 14. Consider the elements ‘X’ (Atomic number 17) and ‘Y’ (Atomic No.20) (i) Write the position of these elements in the modern periodic table giving justification. (ii) Write the formula of the compound formed by the combination of ‘X’ and ‘Y’. (iii) Draw the electron dot structure of the compound formed and state the nature of the bond formed between the two elements. 15. On cutting the body of an organism into many pieces it was observed that many of these pieces developed as new individuals. Name the [Class-X – Science] 286 process and list two organisms in which this process may be observed. Draw a schematic diagram to illustrate the changes that are likely to be observed during the development of new individuals in any one of the following organism named. 16. List any four methods of contraception used by humans. How does their use have a direct effect on the health and prosperity of a family? 17(a) Give the evidence that the birds have evolved from reptiles. (b) Insects, octopus, planaria and vertebrates posses eyes. Can we group these animals together on the basis of eyes that they possess? Justify your answer giving reason. 18(a) Mendel in one of his experiments with tea plants crossed a variety having round seeds with one having wrinkled seeds. Write his observations, giving reasons, of F1 and F2 progeny. (b) List any two contrasting characters other than roundness of pea plants that Mendel used in his experiments with pea plants. 19. Explain with the help of a labelled diagram, the cause of twinkling of stars. 20. A student wants to project the image of a candle flame on the walls of a school laboratory by using a lens : (a) Which type of lens should he use and why? (b) At what distance in terms of focal length ‘f’ of the lens should he place the candle flame so as to get (i) a magnified and (ii) diminished image respectively on the wall? (c) Draw ray diagram to show the formation of the image in each case. 21(a) List three common refractive defects of vision. Suggest the way of correcting these defects. (b) About 45 lac people in the developing countries are suffering from corneal blindness. About 30 lac children below the age of 12 years suffering from this defect can be cured by replacing the defecting cornea 287 [Class-X – Science] with the cornea of a donated eye. How & why can students of your age involve themselves to create awareness about this facts among people? 20. State the reason why carbon can neither form C4+ cations nor C4anions, but forms covalent compounds. Also state reasons to explain why covalent compounds: (i) are bad conductors of electricity? (ii) have low melting and boiling points? 23(a) Give one example each of a unisexual and a bisexual flower. (b) Mention the changes an flavour undergoes after fertilization. (c) How does the amount of DNA remain constant though each new generation is a combination of DNA copies of two individuals. 24(a) Write the name of human male reproductive organ that produces sperms and secretes a hormone. Name the hormone secreted and state its functions? (b) Write the site of fertilization and the part where the zygote gets implanted in the human female. (c) State, in brief, how an embryo gets its nourishment inside the mother’s body. 25. You are asked by your teacher to study the different parts of an embryo of a gram seed. Given below are the steps to be followed for the experiment: I. Soak the gram seeds in plain water and keep them overnight. II. Cut open the soaked seed and observed its different parts. III. Take some dry gram seeds in a petri dish. IV. Drain the excess water. [Class-X – Science] 288 V. Cover the soaked seeds with a wet cotton cloth and leave them for a day. The correct sequence of these steps is : (a) III, I, V, IV, II (b) III, I, II, IV, V (c) III, IV, V, I, II (d) III, I, IV, V, II 26. Which one of the following pairs of vegetable is an example of homologous structures : (a) Potato & sweet potato (b) Carrot and radish (c) Carrot and tomato (d) Tomato and radish 27. Four students P, Q, R and S differently reported the following set of organs to be analogous : P. Forelimb of a frog and forelimb of a lizard Q. Forelimb of a bird and forelimb of a human R. Wings of a parrot and wings of a butterfly S. Wings of a bird and wings of a bat. The two students who have reported correctly are : (a) P and Q (b) Q and R (c) R and S (d) P and S 28. Identify the figures showing the process of budding in yeast. (I) (III) (II) (IV) (a) I, II and III (b) II, III and IV (c) I, II and IV (d) III, IV and I 289 [Class-X – Science] 29. Study the following diagrams showing various stages of binary fission in Amoeba : (I) (II) (III) (a) I, IV, III, II, V (b) I, III, IV, II, V (c) I, II, IV, III, V (d) I, II, III, IV, V (IV) The correct sequence of these diagrams should be : 30. A student adds a few drops of ethanoic acid to test tubes X, Y and Z containing aqueous solutions of sodium chloride, sodium hydroxide and sodium carbonate respectively. If he now brings a burning splinter near the mouth of the test tubes immediately after adding the ethanoic acid in each one of them, in which of the test tube or test tubes the flame gets extinguished? (a) X and Y (b) Y and Z (c) X and Z (d) only Z 31. When you add 2 mL of acetic acid to a test tube containing an equal amount of distilled water and leave the test tube to settle after shaking its contents, then after about 5 minutes what will you observe in the test tube : (a) A white precipitate settling at its bottom. (b) A clear colourless solution. (c) A layer of water over the layer of acetic acid, or (d) A layer of acetic acid over the layer of water. 32. In order to study saponification reaction we first prepare 20% solution of sodium hydroxide. If we record the temperature of this solution just after adding sodium hydroxide flakes to water and also test its nature using litmus, it may be concluded that the process of making this [Class-X – Science] 290 solution is : (a) exothermic and the solution is alkaline. (b) endothermic and the solution is alkaline. (c) endothermic and the solution is acidic. (d) exothermic and the solution is acidic. 33. While studying saponification reaction for the preparation of soap, the teacher suggested to a student to add a small quantity of common salt to the reaction mixture. The function of common salt in this reaction is: (a) reduce the alkalinity of the soap, (b) reduce the acidity of the soap, (c) enhance the cleansing capacity of soap, (d) favour precipitation of soap. 34. A student takes about 6 ml of distilled water in each of the four test tubes P, Q, R and S, then dissolves an equal amount of four different salts namely sodium chloride in ‘P’, potassium chloride in ‘Q’, calcium chloride in ‘R’ each test tube and shakes its contents. The test tubes in which scum (insoluble substance) is formed with soap are: (a) P and Q (b) Q and R (c) R and S (d) Q and S 35. A student has obtained the image of a distant object with a concave mirror to determine its focal length. If he has selected a well illuminated red building as object, which of the following correctly describes the features of the image formed? (a) Virtual, inverted, diminished image in red shade (b) Real, erect, diminished image in pink shade (c) Real, inverted, diminished image in red shade (d) Virtual, erect, enlarged image in red shade 291 [Class-X – Science] 36. A student has obtained an image of a distant object on a screen to determine the focal length F1 of the given lens. His teacher after checking the image, gave him another lens of focal length F2 and asked to focus the same object on the same screen. The student found that to obtain a sharp image he has to move the lens away from the screen. From this finding we may conclude that both the lenses given to the student were: (a) Concave and F1<F2 (b) Convex and F1<F2 (c) Convex and F1<F2 (d) Concave and F1<F 37. A student is observing the diagram showing the path of a ray of light passing through a glass prism. He would find that for all angles of incidence the ray of light bends: (a) towards the normal while entering into the prism and away from the normal while emerging out of the prism. (b) away from the normal while entering into the prism and towards the normal while emerging out of the prism. (c) away from the normal while entering as well as while emerging out of the prism. (d) towards the normal while entering as well as while emerging out of the prism. 38. The path of a ray of light passing through a glass prism is shown below: O Z X M Y N In this diagram the angle of prism, angle of incidence, angle of emergence and angle of deviation respectively have been represented by : [Class-X – Science] 292 (a) O, Y, Z and N (b) P, Y, M and Z (c) O, X, M and Z (d) P, X, Z and N 39. A student has obtained a magnified image of a flame on a screen using a convex lens. To draw the corresponding ray diagram, to show the image formation, which of the following two rays whose paths after refractions are shown he should select? O (I) (II) O O F (III) F (IV) (a) I and II (b) II and III (c) III and IV (d) I and III 40. A student was asked by his teacher to find the image distance from various object distances in case of a given convex lens. He performed the experiment with all precautions and noted down his observations in the following table: S. No. Object distance (cm) Image distance (cm) 1 2 3 4 5 60 48 36 24 18 15 16 21 24 36 6 16 48 293 [Class-X – Science] After checking the observation table the teacher pointed out that there is a mistake in recording the image distance in one of the observations. Find the serial number of the observation having faulty image distance. (a) 2 (b) 3 (c) 5 (d) 6 41. On the basis of their experiment, “To trace the path of a ray of light through a rectangular glass slab,” students of a class arrived at which one of the following conclusions : (a) Angle of incidence is greater than the angle of emergence, (b) Angle of emergence is smaller than the angle of refraction, (c) Emergent ray is parallel to the refracted ray, (d) Incident ray and emergent ray are parallel to each other. 42. Study the following four experimental set-ups, I, II, III and IV for the experiment, “To trace the path of a ray of light through a rectangular glass slab.” P1 P1 P2 (I) P1 P1 P2 P2 P2 (III) (II) (IV) Which of the marked set-ups is likely to give best results (P1 and P2 are the positions of pins fixed on the incident ray)? (a) I (b) II (c) III (d) IV [Class-X – Science] 294 SCIENCE CBSE : 2013-14 Time : 3 hrs. Max. Marks = 90 CLASS X 1. No. of vertical columns- 18 They are called Groups. 2. (i) Heredity 3. (ii) Reproduction (i) Use water in a bucket instead of a running tap for cleaning vehicles. (ii) Use kitchen water (collected after washing fruits and vegetables) for gardening. 4. (i) Plants raised by vegetative propagation can bear flowers and fruits earlier than those produced from seeds. (ii) Desirable characteristics of the parent can be obtained, (iii) Large no. of identical progenies can be obtained. (iv) Propagation also possible for plants that have lost the capacity to form seeds. 5. ABD = i DBC = r 295 [Class-X – Science] A n i B r F C 6. Plastic bags are an example of non-biodegradable substance, if disposed off carelessly they choke the trains, if burnt produce harmful gases. Even if they are recycled they produce inferior plastic which releases carcinogenic toxins. These toxins then enter the food chain and cause irreversible damage to biotic system. Cloth and jute bags are alternatives to plastic bags. Ban of these plastic bags will reduce the release of toxin thus reducing air as well as soil pollution. 7. Biodiversity is existence of variety of species of plants, animals and micro-organisms in a natural habitat. Advantages: (i) The forest help in protection of soil and (ii) retaining sub-soil water. Wild life is a source of life-saving drugs, silk lac and honey. 8. The group of atoms which confer special properties to the compound and replace one or more hydrogen atoms in a hydrocarbon chain are called functional groups. (i) Ethanol Alcohol Ethanol Acid Carboxylic Acid H H H C C H H OH H O C C OH H Ethanol [Class-X – Science] H Ethanoic Acid 296 9. Same as Ques-12 of Set-3 10. (i) I group elements have valency ‘+1’ the formula for their oxide is A+O2-A2O (ii) 13th group elements have valency +3 so the formula for Halides are: eq- A3+Cl-ACl3 (iii) Elements of group 2(A) has valency +2 Elements of group 16(B) has valency -2 Hence the formula is A2+B2-AB. 11. Same as Ques. No. 13 of Set-3. 12. Same as Ques. No. 15 of Set-3. 13. Same as Ques. No. 16 of Set-3. 14. Same as Ques. No. 17 of Set-3. 15. (a) RRGG × rrgg (Round, green) (wrinkled, yellow) RG RG rg rg F1 Progeny rg rg RG RG RrGg RrGg RrGg RrGg All of them are round and green RrGg × RrGg (b) RG Rg rG rg RG Rg 297 rG rg [Class-X – Science] F2 Progeny RG Rg rG rg RG Rg rG rg RRGG RRGg RrGG RrGg RRGg RRgg RrGg Rrgg RrGG RrGg rrGG rrGg RrGg Rrgg rrGg rrgg Ratio is F2 progeny Round green : Round yellow : Wrinkled green : Wrinkled yellow 9 : 3 : 3 : 1 16. Since m = -1 image is real and inverted, hence (a) it is a concave mirror. (b) V = -50cm since m = -1 image is of same size and object is placed at C, image is also formed at C. Hence, Distance of image from object is 0. (c) 1 1 1 f v u v 50cm u 50cm 1 1 1 f 50 50 1 2 f 50 f = 25 cm P C (d) [Class-X – Science] 298 F 50 m 17. Same as Ques. No. 9 in Set-3. 18. Blue colour of the sky is on account of scattering of light of shorter wavelengths by particles in the atmosphere of earth. For an astronaut staying in international space station there would not have been any scattering of light and the sky would have looked dark. 19. Same as Ques. No. 8 of Set-3. 20. Same as Ques. No. 22 of Set-3. 21. Same as Ques. No. 23 of Set-3. 22. Same as Ques. No. 21 of Set-2. 23. Same as Ques. No. 20 of Set-3. 24. Same as Ques. No. 21 of Set-3. 25. B 26. D 27. A 28. D 29. C 30. C 31. A 32. D 33. D 34. C 35. A 36. A 37. D 38. B 39. C 40. B 41. C 42. D 299 [Class-X – Science] SCIENCE CBSE : 2013-14 CLASS X 1. No. of horizontal rows = 7 Horizontal rows are called = Periods 2. DNA 3. Same as Q. No. 3 of Set-1. 4. Four modes of as sexual reproduction:(i) Fission (iii) Spore formation (ii) Budding (iv) Vegetative propagation. 5. Same as Q. No. 5 of Set-1. 6. Same as Q. No. 6 of Set-1. 7. Problems due to construction of big dams:(a) Social Problem - They displace a large no. of place without adequate compensation or rehabilitation. (b) Economic Problem - They swallow up huge amounts of public money without the generation of proportionate benefits. (c) Environmental Problem - They contribute enormously to deforestation and the loss of biological diversity. There should be equitable distribution of water and dams should be built in a more sustainable way. [Class-X – Science] 300 8. Farmers use pesticides in agriculture. These chemicals remain is soil for a long time and are taken up by the plants from the soil along with water and minerals. From plants, they enter the food chain. Grass Sheep or Goat (absorbs chemicals (Receive chemicals from soil) with food) Man (Through milk and meat) 9. Four methods of contraception:(i) Barrier method - Condom (ii) Chemical method - Oral pills (iii) Surgical method - Tubectomy/Vasectomy (iv) Intra-uterine method - Copper T Using contraceptive devices have a direct effect on the health and prosperity of family as:It helps to control birth and to check frequent pregnancies as it has very bad effect on the mother’s health. It also prevents STD’s Families also prosper as reduction in no. of children enables them to take care of the children and provide them the required facilities for their growth and development. 10. (a) (b) 11. (i) Stamen (ii) Pollen grains (iii) Pistil (iv) Egg. Flower is the reproductive part of the plant, hence helps in reproduction. (a) A fossil bird called Archaeopteryx looks like a bird but it has many other features which are found in reptiles. It has feathered wings like those of birds but teeth and tail like those of reptiles. It is, therefore, a connecting link between the reptiles and birds and hence suggests that the birds have evolved from the reptiles. (b) Insects, octopus, planaria and vertebrates possess eyes but we can not group these animals together on the basis of eyes that they possess because structure of eyes in each of these organisms in different which suggests their separate evolutionary origins. 301 [Class-X – Science] 12. (a) Observations:- (i) In F1 generation, all plants were tall and no medium height that is only one of the parental traits was seen, not some mixture of the two. Tall TT T × × Dwarf tt t T Tt Tt Tt t Tt (ii) In F2 generation, all plants were tall. One quarter of them were short, that is, both the tallness and shortness traits were expressed. Tt T Tt t t t Tt Tt Tt Tt (Tall) (Tall) (Tall) (Tall) Phenotype - Genotype - 3:1 1 (TT) : 2 (Tt) : 1 (tt) 13. Laws of Refraction of Light (i) The incident ray, the refracted ray and the normal to the surface of separation of two media at the point of incidence, all lie in the same plane. (ii) The ratio of sine of angle of incidence to the sine of angle of refraction is constant. [Class-X – Science] 302 sin i n21 sin r Absolute refractive index = 1.5 x Speed of light in vaccum Speed of light in medium 3 108 ms 1 x 3 108 ms 1 2 108 ms 1 1.5 Speed of light in medium = 2×108 ms-1 14. Spherical mirror Magnification = -1 (image is real, of same size) Image distance = -40cm m v u (i) Concave mirror (ii) Real image (iii) m v u [v = -40 cm] -u = 40 cm u = -40 cm F (iv) C 303 [Class-X – Science] 15. Due to atmospheric refraction, sum is a visible to us about 2 minutes before the actual sunrise and about 2 minutes after the actual sunset. Observero Horizon 16. Name - Alkene General formula - CnH2n Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons. C2 H 4 Ethane Ni H2 Hydrogen C2 H 6 473k Ethane 17. Functional Group - An atom or a group of atoms which makes an organic compound reactive and decides its functions or properties is called a functional group. 18. (a) Functional group Formula Alcohol —OH Aldehyde –C Ketone –C– O Carboxylic Acid O –C–OH H O (i) Valency - The combining capacity of an element. [Class-X – Science] 304 (ii) Atomic size - Radius of an atom of an element. Distance between the centre of atom and the outermost shell. (b) Along a period - Valency of the elements first increases (from 1 to 4) and then decreases - Atomic size of the elements decrease. 19. KLMN (i) A (At. no. - 17) - 2 8 7 B (At. no. - 19) - 2 8 8 1 ‘A’ has 7 electrons in its outermost shell and has used K L M (3) shells. A = 7th Group, IIIrd Period. ‘B’ has 1 electron on its outermost shell and has used K L M N (4) shells. B = 1st Group, IVth Period (ii) Formula of compound A and B A - 17 - 2 8 7 Valency = 1 B - 19 - 2 8 8 1 Valency = 1 Compound formed = BA [B+ A-] (iii) Electron dot structure of the compound .. :A .. : + B A– . B .. – [B+] [:A .. :] Nature of the bond - Ionic (Because there is transfer of electrons) 20. C is a tetravalent element i.e. it has 4 electrons in its outermost shell. It needs 4 electrons to attain stable configuration. 305 [Class-X – Science] If carbon gains 4 electrons, it would be difficult for the nucleus with six protons to hold on to ten electrons, that is, four extra electrons. So, it cannot form C4- anions. If carbon loses 4 electrons, it would require a large amount of energy to remove four electrons leaving behind a carbon cation with six protons in its nucleus holding on to just two electrons. So, it cannot form C4+ cations. Carbon overcomes this problem by sharing its valence electrons with other atoms of carbon or with atoms of other elements forming covalent compounds. (i) Covalent compounds are bad conductors of electricity because they do not contain ions or free electrons for conduction. (ii) Covalent compounds have low melting and boiling points because molecules of a covalent compounds are held together by relatively weaker forces as compared to that in ionic compounds, so, less energy is required to overcome these forces. (a) (i) Ovary (ii) Fallopian tube (oviduct) (iii) Uterus (b) After fertilisation, ovum forms zygote which fixes itself into the wall of uterus and starts to develop as an embryo. The embryo tisuses and mother’s uterus wall tissue form placenta. The developing embrya gets nutrients and oxygen through placenta from the mother. (a) Unisexual flower - Papaya Bisexual flower - Hibiscus (b) After fertilisation [the ovary changes into fruit and the ovules change into seeds] The fertilised zygote divides and gives rise to embry. Thus a seed contains a tiny embryo. The embryo contains radicle and plumule and cotyledon. [Class-X – Science] 306 (c) The amount of DNA remain constant through each new generatioin is a combination of DNA copies of two individuals because of the following reason : The reproductive cells cotnain half the number of chromosomes (HAPLOID) (Diploid) 46 Chromosomes 46 Chromosomes (Diploid) (Reproductive cell) (n) (Reproductive cell) 23 Chromosomes 23 (Haploid) Chromosomes (n) (Haploid) (2n) 46 Chromosomes 23. Same as Q.No. 21 of Set III. 24. (a) Concave mirror because concave mirrors produce real image. (b) At F (c) C F P At infinity 307 [Class-X – Science] (d) Yes, he can use this mirror to project a diminished image of the candle flame on the same wall by positioning the object beyond the centre of curvature C. 25. b 26. c 27. d 28. a 29. a 30. c 31. d 32. c 33. d 34. c 35. b 36. c 37. b 38. c 39. d 40. b 41. a 42. d [Class-X – Science] 308 SCIENCE CBSE : 2013-14 CLASS X 1. Elements of Group 1 have one valance electron in the outermost shell whereas elements of group-2 have two electrons in the outermost shell. 2. He gave the theory of Natural Selection. 3. (i) (ii) For future generators For sustainable development. 4. (i) Budding (ii) Spore formation (iii) Regeneration (iv) Vegetative Propagation. A i r C B ABC i CBF r P F 5. 6. Two practices that should be followed : (a) Plant more tress (b) Stop the use of polythene bags. 309 [Class-X – Science] These practices will help in bringing more rain, increasing the oxygen content thereby reducing air pollution. Also, polythene bags are nonbiodegradable so, that using them will reduce soil pollution. Both the practices help in saving the environment. 7. Excessive exploitation of natural resources with short term aims is the basis of affluent life style. Example : Use of air-conditioners and refrigerant add to CFC in the atmosphere which causes ozone depletion. Similarly excessive use of diesel and petrol adds to harmful gases causing air pollution. 8. Several pesticides used to protect our crops from diseases and pests are washed down into the soil or into water bodies. From the soil, these are absorbed by the plants and from the water bodies these are taken up by aquatic plants and animals. Human beings occupy the top level in any food chain. Therefore, maximum concentration of the harmful chemicals get accumulated in our bodies. This phenomenon is called Biological magnification. 9(a) (i) The incident nay, refracted ray and the normal at the point of incidence all lie in the same plane. (ii) The ratios of sine of angle incidence and the sine of angle of refraction is constant for a given pair of medium. ie sin i = n 21 sin r Where n21 is called refractive index of medium 2 w.r.t. medium. (b) Given c = 3×108 m/s v=? u = 1.5 1.5 = [Class-X – Science] 3 × 108 V 310 V = 3 × 108 1.5 V = 2×108 m/s 10. Given M = –1 it shows that it is real and inverted image. V = –30 cm. (i) Concave Mirror (ii) m = –v u –1 = – (–30) u –1 = 30 u u = –30 cm 1 1 1 = f v u 1 1 1 = f –30 –30 1 –2 –1 = f 30 15 f = –15 cm (iii) Real and inverted and of same size. 311 [Class-X – Science] P F C (iv) 11. Esters are sweet smelling substances. They are prepared when a carboxylic acid reacts with an alcohol in presence of a mineral acid. H CH 3COOH + C2 H5OH CH3COOC2 H5 H 2O eq- Ethanoic acid Ethanol Ester Uses : (i) in making perfumes (ii) are flavouring agents. 12. Name – Alkanes Gen formula CnH2n+2 Addition Reaction – Addition of hydrogen to unsaturated hydrocarbons in the presence of catalyst such as Palladium to give saturated hydrocarbons. R R C=C R R H H +H2 Unsaturated hydrocarbon 13(a) (i) Pd R– C – C – R H R Saturated hydrocarbon Valency is the no. of electrons in the outermost (valence) shell. [Class-X – Science] 312 (ii) Atomic size is the distance between the centre of atom and the outermost shell of isolated atom. (b) Valency increases when we move from left to right in a period while atomic size decreases. 14. Element X with atomic no. 17 (i) Electronic Configuration 2, 8, 7 Since it has seven electrons in the outermost shell, it belongs to 17th group. Since it has three shells it belongs to 3rd period. Element Y – atomic no. 20 Electronic Configuration 2, 8, 8, 2 Since it has two electrons in the outermost shell and four shells it belongs to 2nd group and 4th period. (ii) X– Y2+ X2 Y 2+ [y] × Nature of bonds Ionic Bond (iii) × 15. Process – Regeneration eq- Planaria and spirogyra 313 [Class-X – Science] 16. Techniques cervical cap. (i) Mechanical barrier method IUD, condoms, (ii) Hormonal methods oval pills, implants which suppresses production of ovum. (iii) Surgical method Vasectomy in males, tubectomy in females. (iv) Chemical methods Creams, spermicidal jellies and vaginal pills. Usage of above mentioned methods have a direct effect on the health and prosperity of family as : (i) it provides awareness to both male and female regarding fertility regulating methods. (ii) Reduction in no. of children so that they are reared with better resources. (iii) Preventing of STD’s. [Class-X – Science] 314 17(a) Archaeopteryx a fossil looks like a bird but it bears features which are found in reptiles. This shows that birds have been evolved from reptiles. E v id en ce fro m F o ssils (b) Eyes perform same function in all the organisms but other organs present in them may attribute different features and characteristics to them e.g.. insects respire through tracheoles whereas birds have lungs so, we cannot categorise organisms based on just one feature of presence of eyes. 18(a) RR × (Round) R r r (wrinkled) R r r F1 Progeny R R r Rr Rr r Rr Rr Rr × R r R r R All seeds are Round. r F2 Progeny R r R RR Rr r Rr rr Ratio of round seeds to wrinkled seeds is 3:1 (b) Other contrasting characters can be Green and yellow seeds tall and dwarf plants. 315 [Class-X – Science] 19. Since stars are very far away from the earth, they behave as a point. Atmosphere is made of several layers and their refractive indices keep on changing continuously : Light rays from the start keep on changing their path continuously. As a consequence the number of rays (or light energy) entering in the pupil of the eye goes on changing with time and the stars appear twinkling Apparent star position Star Refractive Index increasing D 20(a) As the image is being formed on the screen, it is a real image so the lens should be convex lens. (b) (i) To get magnified image the candle flame should be placed at focus of lens. (ii) To get a diminished image the candle flame should be at an infinite distance. (c) (i) Magnified image. 2f [Class-X – Science] 2f O f 316 (ii) Diminish image. 2f 21(a) DEFECTS f o f 2f WAY OF CORRECTING DEFECTS (i) Myopia Concave lens (ii) Hypermetropia Convex lens (iii) Presbyopia Bifocal lens (b) We can organise eye donation camps by social workers in our locality and wholeheartedly participate in the camp too. Forms should be filled by the participants pledging to donate their eyes after death. We should encourage our family members and friends too for the same. It is because eye donation could give new light to no. of blind people. Eye donation is a noble cause and we should propagate the idea. 22. To form C4+ cations it would require a large amount of energy to part with four electrons. Similarly it would be difficult for the nucleus of C to hold on to ten electrons if it forms C4– anions. (i) Covalent compounds have covalent bonds formed by sharing of electrons which have weak force of attractions in them, thus with low amount of energy can be easily broker thus have low M.P. and B.P. As there is sharing of electron there is no free ion thus they are also bad conductors of electricity. 317 [Class-X – Science] 23(a) Unisexual Papaya Bisexual Hibiscus (b) After fertilisation the ovule develops into a seed containing embryo and the ovary grows rapidly and ripens into a fruit. (c) Parents are deploid ie each having two sets of chromosomes. During inheritance the zygote receives 1 set each from the male gamate and female gamate (As male gamates and female gamates have one set of chromosome through the process of meiosis) and thus no. of chromosomes in embryo is restored. 24(a) Testis Hormone secreted Testosterone Function Production of sperms (b) Site of fertilisation Fallopian tube Zygote gets implanted in the uterus in human female. (c) After implantation a disc like special tissue develops between the uterus wall and embryo called Placenta. The exchange of nutrients, oxygen and waste products between the embryo and the mother takes place through the Placenta. 25. d 26. b 27. c 28. c 29. b 30. d 31. b 32. a [Class-X – Science] 318 33. d 34. c 35. c 36. b 37. a 38. c 39. d 40. a 41. d 42. d 319 [Class-X – Science]
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