SCIENCE
CLASS: VII
TOPIC: (HEAT AND TEMPERATURE)
Q-1 What is heat?
Ans : Heat is a form of energy that produces a feeling of hotness. It is measured in Joule or
Calorie. Heat flows from one body to another due to the temperature difference between
the two.
Q-2 What is temperature? What are the units used to measure the temperature?
Ans : A reliable measure of the hotness of an object is its temperature. Temperature is
measured by a device called thermometer. It is measured in degree Celsius (0C), Fahrenheit
(0F) and Kelvin ( SI units)
Q-3. How are heat and temperature of a substance related to each other ?
Ans : Heat is the total energy of the molecular motion of the substance. Temperature is the
measure of the average energy of the molecular motion in a substance. When you heat a
substance, it increases the motion of the vibrating molecules of the substance thereby
increasing the temperature of the substance.
Q-4. What are the effects of heat?
Ans : Heat cause many change in living and non-living thing. They are
1. Heat causes an increase in temperature
2. Heat causes expansion in a substance
3. Heat can change the state of a substance
4. Heat can bring about a chemical change
Q-5. What are the different thermometer scales?
Ans :The different thermometer scales are
1
(a) The centigrade or Celsius scale: It is introduced by Celsius, is usually used in scientific
laboratories. In this scale the lower fixed point or the ice-point is 0°C and the steam-point
100°C.
(b) The Fahrenheit scale: It is suggested by Gabriel Fahrenheit, is usually used in clinical and
meteorological purposes. Here, the ice-point and the steam-point are correspondingly
marked as 32°F and 212°F.
(c) Absolute scale or Kelvin scale: It is designed by Lord Kelvin, is used internationally in
modern scientific world. In this scale the ice-point is marked 273K and the steam-point
373K.
Q-6. What are different types of thermometer?
Ans : Thermometer: It consist of long narrow glass tube having fine bore.There is a glass
bulb filled with liquid mostly mercury at the one end and sealed at other end. There is small
bend just above bulb called Kink. The Kink does not allow the mercury to fall as soon as
taken out from our mouth.
(i). Laboratory Thermometer: It ranges from -10oC to 110oC
(ii) Clinical thermometer: It is used to measure body temperature. It ranges from 35oC to
42oC and 94oF to 108oF.
(iii) Alcohol thermometer used to measure temp. from -125oC to 50oC.
Q-7. Why is mercury preferred in thermometers?
Ans : Mercury used due to following reasons
(i) It expand uniformly
(ii) It does not stick to the wall of the thermometer
(iii) It is shiny and easy to see
(iv) It remain liquid at room temperature.
Q-8. What are the different temperature scales used? What is the relation between them ?
Ans : Different temperature scale used are :
Kelvin Scale (K)
2
Degree Centigrade ( 0C)
Fahrenheit (F)
K = 273 + 0C
Example 7 0C will be in Kelvin scale be : K = 273 + 7 = 280 K
Q-9. What are different mode of transfer of heat?
Ans : Heat flows from a body of higher temperature to body with lower temperature till
both bodies attain same temperature.
There are three mode of transfer of heat
1. Conduction: The mode of transfer of heat from molecules to molecules without
movement of particles.. Conduction takes place in solid as its molecules ate closely
packed. Solids, metals and alloy are good conductor. Nonmetals, plastic glass are bad
conductor of heat.
2. Convection: The mode of transfer of heat from molecules to molecules with
movement of particles. In liquids and gasses heat transferred by convection as
molecules are far apart from each other.
3. Radiation: The mode of transfer of heat that does not require any material medium.
Heat of sun reach the earth by radiation.
Q-10. What are the conditions necessary for conduction of heat?
Ans : The conditions necessary for conduction of heat are :
1. The two bodies should be in solid state
2. The two bodies should be in contact or touch with each other
3. Their temperature should be different ( for heat to flow)
Q-11. What is land and sea breeze explain?
Ans : During the day, the land gets heated faster than the water. The air over the land
becomes hotter and rises up. The cooler air from the sea rushes in towards the land to take
its place. The warm air from the land moves towards the sea to complete the cycle. The air
from the sea
3
is called the sea breeze.
At night, The water cools down more slowly than the land. So, the cool air from the land
moves towards the sea. This is called the land breeze
Q-12. How does the heat from the sun reach us?
Ans : It cannot reach us by conduction or convection as there is no medium such as air in
most part of the space between the earth and the sun. From the sun the heat comes to us
by another process known as radiation.
Radiation can take place whether a medium is present or not.
Q-13. In summer we prefer light-colored clothes and in winter we usually wear dark-colored
clothes. Why?
Ans : Dark surfaces absorb more heat and, therefore, we feel comfortable with dark colored
clothes
in the winter. Light colored clothes reflect most of the heat that falls on them and,
therefore, we feel more comfortable wearing them in the summer.
Q-14. How Woolen clothes keep us warm in winter ?
Ans : Woolen clothes keep us warm during winter. It is so because wool is a poor conductor
of heat and it has air trapped in between the fibers
Q-15. Why one thick blanket is less warm up than two thin blankets joined together?
Ans : There is a layer of air in between the blankets. Since air is bad conductor of heat
prevent body heat to escape out.
Q-16. How is heat transferred in solids, liquids and gases?
Ans : The heat flows from a body at a higher temperature to a body at a lower temperature
In solids, generally, the heat is transferred by conduction. In liquids and gases the heat is
transferred by convection. No medium is required for transfer of heat by radiation
Q-17. In places of hot climate it is advised that the outer walls of houses be painted white.
Explain.
4
Ans : In places of hot climate it is advised that the outer walls of houses be painted white
because a light color absorb very less radiant heat and we feel comfortable inside such
houses due to lower temperature inside house.
Q-18. Explain why wearing more layers of clothing during winter keeps us warmer than
wearing just one thick piece of clothing.
Ans : In between the layers of cloths there is trapped air. As air is bad conductor of heat so
the outside low temperature do not get transferred to body as well as prevent our body
heat to escape outside. Hence more layers of cloths keep us warmer during cold winter.
Q-19. What are conductors and insulators?
Ans : Conductors: Materials which allow heat to pass through it are called conductor or
good conductor of heat, such as iron, copper, aluminum, etc. All metals are good conductors
of heat.
Since metals are the good conductor of heat that’s why kitchen utensils are made of metals or
alloys of metals.
Insulators: Materials which do not allow heat to pass through them are called bad conductor
or poor conductor of heat. They are also called insulators. Example: rubber, wood, plastic,
etc. This is the cause that handles of frying pan or other kitchen utensils are made of plastic.
Q-20. Convert the following temperature from degree Celsius to Kelvin.
1. Ans : 750 C to Kelvin
00 Celsius = 273 K
750 C = 273 + 75
= 348 K
2. 450 C to Kelvin
00 Celsius = 273 K
450 C = 273 + 45
= 318 K
Q-21. Convert the following temperature from Kelvin to degree Celsius.
1. Ans : 280 K to degree Celsius
273 K = 00 Celsius
280 K = 280 – 273
= 7 0 Celsius
5