NCERT Solutions for class 7 Science Heat

Exercise

1. State similarities and differences between the laboratory thermometer and the clinical thermometer.

Ans: Similarities: Both clinical thermometer and laboratory thermometer are used to measure the temperature and they contain mercury inside.

Differences: Clinical thermometer is used to measure body temperature. While laboratory thermometer is used to measure the temperature of objects that has temperature higher or lower than body temperature.

2. Give two examples each of conductors and insulators of heat.

Ans: Conductors of heat: Copper and Aluminum

Insulators of heat: Wood and paper

3. Fill in the blanks :

1. The hotness of an object is determined by its temperature.
2. Temperature of boiling water cannot be measured by a clinical thermometer.
3. Temperature is measured in degree Celsius.
4. No medium is required for transfer of heat by the process of radiation.
5. A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of conduction.
6. Clothes of dark colours absorb more heat better than clothes of light colours.

4. Match the following:

i. Land breeze blows during	a. summer
ii. Sea breeze blows during	b. winter
iii. Dark coloured clothes are preferred during	c. day
iv. Light coloured clothes are preferred during	d. night

Ans:

i. Land breeze blows during	a. night
ii. Sea breeze blows during	b. day
iii. Dark coloured clothes are preferred during	c. winter
iv. Light coloured clothes are preferred during	d. summer

5. Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing .

Ans: Wearing more layers of clothing during winter keeps us warmer because it doesn’t allows our body heat to easily pass through it because it contains air spaces and air is the bad conductor of heat.

7. In places of hot climate it is advised that the outer walls of houses be painted white. Explain.

Ans: Since light color reflects most of the heat energy, it protects the house from rising its temperature inside and makes it comfortable to live. Thus, in hot climates it is advised to paint the outer wall with white paint.

8. One litre of water at 30°C is mixed with one litre of water at 50°C. The temperature of the mixture will be

(a) 80°C (b) more than 50°C but less than 80°C (c) 20°C (d) between 30°C and 50°C

Ans: (d) B between 30°C and 50°C

9. An iron ball at 40°C is dropped in a mug containing water at 40°C. The heat will

1. flow from iron ball to water.
2. not flow from iron ball to water or from water to iron ball.
3. flow from water to iron ball.
4. increase the temperature of both.

Ans: (b) not flow from iron ball to water or from water to iron ball.

10. A wooden spoon is dipped in a cup of ice cream. Its other end

1. becomes cold by the process of conduction.
2. becomes cold by the process of convection.
3. becomes cold by the process of radiation.
4. does not become cold.

Ans: (d) does not become cold

11. Stainless steel pans are usually provided with copper bottoms. The reason for this could be that

1. copper bottom makes the pan more durable.
2. such pans appear colourful.
3. copper is a better conductor of heat than the stainless steel.
4. copper is easier to clean than the stainless steel.

Ans: (c) copper is a better conductor of heat than the stainless steel.

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