NCERT Solutions For Class 7 Science Chapter 4 – Heat

Oct 26, 2020

NCERT Solutions For Class 7 Science Chapter 4 – Heat

Learn from School Connect Online in this chapter we will learn about heat where heat is a form of energy which makes the substance hot. In winter, it is our common experience that we feel cold inside the house and if we come out in front of sun rays, then we feel warm.

Exercise Questions

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

Solution:

Similarities

• Both are made of glass and consist of long narrow glass tube.
• At one end both of them have a bulb.
• Bulbs of both the thermometers consist of mercury
• Celsius scale is present in both the thermometer

Differences

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

Solution:

Conductors: Iron and Copper

Insulators: Plastic and wood

3.Fill in the blanks :

(a) The hotness of an object is determined by its __________.

Sol : The hotness of an object is determined by its temperature.

(b) Temperature of boiling water cannot be measured by a _____________ thermometer.

Sol : Temperature of boiling water cannot be measured by a clinical thermometer.

(c) Temperature is measured in degree ______________.

Sol : Temperature is measured in degree Celcius.

(d) No medium is required for transfer of heat by the process of __________.

Sol : No medium is required for transfer of heat by the process of radiation.

(e) A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of ______________.

Sol : A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of conduction.

(f ) Clothes of ______________ colours absorb more heat better than clothes of light colours.

Sol : Clothes of dark colours absorb more heat better than clothes of light colours.

4. Match the following :

Solution:

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

Solution:

More layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing because air gets trapped in-between layers. As air is a bad conductor of heat it does not allow the escape of the heat from the body.

6. Look at Fig. 4.13. Mark where the heat is being transferred by conduction, by convection and by radiation.

Solution:

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

Solution:

In places of hot climate, it is advised that the outer walls of houses be painted white because white colour reflects back most of the heat that is incident on it as white is a poor absorber of heat. This helps in keeping the house cool.

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

Solution:

The temperature of the mixture will be between 30°C and 50°C because hot water loses the heat and simultaneously cold water gains heat this keeps the temperature in 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

(a) flow from iron ball to water.

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

(c) flow from water to iron ball.

(d) increase the temperature of both.

Solution:

Answer is (b) not flow from iron ball to water or from water to iron ball because both of them have the same temperature of 40°C.

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

(a) becomes cold by the process of conduction.

(b) becomes cold by the process of convection.

(c) becomes cold by the process of radiation.

(d) does not become cold.

Solution:

The answer is (d) does not become cold because wood is a bad conductor of heat.

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

(a) copper bottom makes the pan more durable.

(b) such pans appear colourful.

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

(d) copper is easier to clean than stainless steel.

Solution:

The answer is (c) copper is a better conductor of heat than the stainless steel.

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