Heat
ASSIGNMENT
1. Fill in the blank spaces by choosing correct words from the list given below :
List : vacuum, more, rollers, less, boiling, conductor shining, hot, linear, free, gases,
glass, solids.
(i) Liquids expand .......................... than solids, but .......................... than gases.
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(ii) We use copper coils in the car radiators, because copper is a good ..........................
of heat.
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(iii) A thick glass tumbler cracks when .......................... water is poured in it, due to
uneven expansion of .......................... .
(iv) Convection is not possible in case of .........................., because molecules are not
.......................... to leave their positions.
(v) Convection can take place in liquids and ...........................
(vi) Liquids and gases do not have .......................... expansion.
(vii) Bridges are mounted on .......................... to prevent collapse of pillars.
(viii) .......................... bodies are poor absorbers of radiant heat.
(ix) Radiant heat can easily pass through ...........................
(x) The process due to which a liquid changes into gas at fixed temperature, is called
...........................
2. Write ‘T’ for true and ‘F’ for false in front of the following sentences :
(i) All solids have same linear expansion, when heated through same range of
temperature.
(ii) The coils of car radiators are blackened because black bodies are good radiators of
heat.
(iii) A partially inflated balloon gets deflated, when kept near a working room heater.
(iv) In winter, the water near the surface of pond is cooler than water at the bottom of
pond.
(v) The expansion of gases is more than the liquids.
(vi) Thermos flask can keep hot things hot, but not cold things cold.
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(vii) Expansion of all gases for same range of temperature is the same.
(viii) The glass chimney of kerosene oil lamp cracks when a drop of rain falls on it.
(ix) Mud houses remain cold in winter.
(x) The radiant heat can easily pass through the air.
3. Statements given below are incorrect. Write the correct statements :
(i) In a bimetallic strip brass expands less than iron.
(ii) A thermometer is an instrument which measures amount of heat energy in a body.
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(iii) Water gets heated, by the process of conduction.
(iv) Alcohol thermometer are more accurate, because alcohol expands less than
mercury.
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(v) A wooden bench feels colder than an iron bench in winter.
(vi) During transmission of heat by conduction, the particles of a material actually
move towards the sources of heat.
(vii) The liquid through which conduction is possible at room temperature, is alcohol
(viii) The temperature at which a gas changes into liquid state, is known as boiling
point.
(ix) The upper standard point on kelvin scale, is 273 K.
(x) A shining body is a good absorber of heat.
4. Tick (
) the most appropriate answer.
(i) A device in which heat losses are minimised, is :
(a) thermometer
(b) solar cooker
(c) radiator
(d) thermos flask
(ii) The material through which radiant heat can pass easily, is :
(a) glass
(b) copper
(c) aluminium
(d) water
(iii) The process due to which heat from the sun, reaches us, is :
(a) conduction
(b) convection
(c) contraction
(d) radiation
(iv) The material, which is a bad conductor of heat, is :
(a) zinc
(b) copper
(c) mercury
(d) plastic
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(v) Black surfaces are :
(a) good absorbers of radiant heat
(b) good radiators of radiant heat
(c) poor absorbers of radiant heat
(d) good absorbers and good radiators of radiant heat
(vi) Only liquid which can be heated by conduction, is :
(a) benzene
(b) water
(c) mercury
(d) alcohol
(vii) Fastest mode of transmission of heat is :
(a) convection
(b) conduction
(c) radiation
(d) evaporation
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(viii) During day time, the air becomes warm due to the process of :
(a) condensation
(b) conduction
(c) convection
(d) radiation
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(ix) A bimetallic strip is made of brass and iron. On heating :
(a) brass expands more than iron.
(b) iron expands more than brass.
(c) both expand equally.
(d) brass expands, but does not contracts
(x) Loosely wollen clothes keep you warm, because :
(a) loose clothes give out heat energy.
(b) trapped air in loose clothes is good conductor of heat.
(c) trapped air in loose clothes, is bad conductor of heat.
(d) trapped air in loose clothes allows the heat from
surrounding to flow in.
5. Find the odd one out. Give a reason for your answer.
(i) petrol, diesel, kerosene, mercury.
(ii) contraction, conduction, convection, radiation.
(iii) wood, iron, plastic, mica.
(iv) copper, silver, paper, aluminium
6. (i) Heat energy raises the temperature of a body. There are two other changes, which
heat energy can bring about. Name these changes.
(i) (a) What is a thermometer?
(b) How many degrees are in a laboratory celsius thermometer?
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(c) What do you understand by the following and state their numerical values?
(1) Lower standard point
(2) Upper standard point
(d) State three reasons for using mercury in thermometer.
7. (i) What do you understand by the term thermal expansion?
(ii) A solid can have three kinds of thermal expansions. Name each kind and define
them.
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8. By drawing a diagram, describe an experiment to prove that the solids expand on
heating.
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9. Explain the following :
(i) Why are girders of the bridges mounted on rollers?
(ii) Why are electric transmission wires stretched tightly, when they are laid in winter
season?
(iii) Why is cement floor laid in small slabs leaving a small space, rather than a complete
block?
(iv) Why is the iron rim heated to red hot, before mounting it on a wooden wheel?
(v) Why does a thick glass tumbler crack when melting ice is placed in it?
(vi) Why does glassware made from borosil glass not crack, when heated directly on
flame?
(vii) Why are small gaps left behind walls while mounting girder on them?
(viii) Why are tiny gaps left in between rails on a railway line?
(ix) Why do the solids expand least as compared to liquids or gases?
10. (i) What is a bimetallic strip?
(ii) Draw diagrams for a bimetallic strip of brass and invar, when it is, (i) heated to
100 °C, (ii) cooled to –20 °C.
(iii) Draw a neat diagram for the electric fire alarm.
11. Give reasons :
(i) Why do soft drink bottles burst in summer heat?
(ii) Why does a partly inflated balloon get fully inflated, when placed in boiling
water?
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(iii) Why does a liquid or a gas has cubical expansion only and no linear or superficial
expansion?
(iv) Why do gases expand far more than liquids or solids?
12. (i) Define the following terms :
(a) Fusion
(b) Solidification
(c) Melting point
(d) Vaporisation
(e) Boiling point
(f) Condensation
(g) Evaporation
(h) Sublimation
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(ii) Give one difference between a gas and a vapour.
13. (i) Name three modes of transmission of heat.
(ii) Which of the above modes of transmission :
(a) is fastest.
(b) is slowest.
(c) takes place without any medium.
(d) takes place with the movement of molecules.
(e) takes place without the actual movement of molecules.
14. Describe an experiment to prove that copper is a good conductor and glass is a bad
conductor of heat.
15. Describe an experiment to prove that gases expand on heating. Draw an appropriate
diagram.
16. (i) Define conduction of heat energy.
(ii) Describe an experiment to prove that conduction takes place in solids. Draw an
appropriate diagram.
17. (i) What do you understand by the term good conductor of heat?
(ii) Name four good conductors of heat.
(iii) What do you understand by the term bad conductor of heat?
(iv) Name four bad conductors of heat.
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18. Explain the following :
(i) Why are plastic or wooden handles provided to cooking vessels?
(ii) Why are cooling coils of a refrigerator made from copper?
(iii) Why do birds puff up their feathers in winter?
(iv) Why are two thin blankets warmer than a single thick blanket?
(v) Why does an iron chair placed in the sun feel hotter than a wooden chair?
(vi) Why are the mud houses with thatched roofs cooler in summer than concrete
houses?
(vii) Why does water in ponds feel hotter near its surface than its base during summer?
(viii) A blanket keeps a person warm, but when wrapped around ice, it does not allow
it to melt? Explain.
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19. (i) What do you understand by the term convection?
(ii) By drawing a diagram, describe an experiment to prove that gases get heated by
convection.
20. (i) What do you understand by the term ventilation?
(ii) How do convection currents help in the ventilation of a room?
21. What do you understand by the following terms?
(i) Radiation
(ii) Radiant heat
22. Describe an experiment to prove that black bodies are good absorbers and good
radiators of heat energy. Draw an appropriate diagram.
23. Draw a neat and labelled diagram of thermos flask. State two ways in which heat losses
are minimised by :
(i) Conduction
(ii) Convection
(iii) Radiation
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