Heat class 7 Science NCERT Solutions

Heat class 7 Science NCERT Solutions: Heat is the chapter 4 from class 7 Science NCERT. Here you'll get Heat class 7 Heat class 7 Science NCERT Solutions. 

Heat class 7 Science Main Points/Heat class 7 Science Notes

Our sense of touch is not always a reliable guide to the degree of hotness of an object. Temperature is a measure of the degree of hotness of an object.

Thermometer is a device used for measuring temperature. Clinical thermometer is used to measure our body temperature. The range of this thermometer is from 35°C to 42°C. For other purposes, we use the laboratory thermometers. The range of these thermometers is usually from –10°C to 110°C. The normal temperature of the human body is 37°C.

The heat flows from a body at a higher temperature to a body at a lower temperature. There are three ways in which heat can flow from one object to another. These are conduction, convection and radiation.

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.

The materials which allow heat to pass through them easily are conductors of heat. The materials which do not allow heat to pass through them easily are called insulators.

Dark-coloured objects absorb more heat than the light-coloured objects. That is the reason we feel more comfortable in light-coloured clothes in the summer.

Woollen 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 fibres.

Class 7 Science Chapter 3 Heat Questions Answers

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

Ans: Similarities:

(i) Both thermometers consist of long narrow uniform glass tubes.

(ii) Both have a bulb at one end.

(iii) Both contain mercury in bulb.

(iv) Both use Celsius scale on the glass tube.

Differences:

(i) A clinical thermometer reads temperature 35°C to 45°C while the range of laboratory thermometer is -10°C to 110°C.

(ii) Clinical thermometer has a kink near the bulb while there is no kink in the laboratory thermometer.

(iii) Due to kink mercury does not fall down on its own in clinical thermometer.

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

Ans: Conductors—aluminium, iron 

          Insulators—plastic, wood.

3. Fill in the blanks :

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

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

(c) Temperature is measured in degree ______________.

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

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

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

Ans:

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

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

(c) Temperature is measured in degree celcius.

(d) 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 conduction.

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

NCERT Solutions of Heat class 7 Science

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                              (d) night

(ii) Sea breeze blows during                               (c) day

(iii) Dark coloured clothes are preferred during        (b) winter

(iv) Light coloured clothes are preferred during        (a) summer

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

Ans: More layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing because air gets trapped in-between layer. 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.

Ans:

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

Ans: 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.

NCERT Solutions for Heat class 7 Science

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: 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.

Ans: Not flow from iron ball to water or from water to iron ball

10. A wooden spoon is dipped in a cup lof 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.

Ans: Does not become cold.

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 the stainless steel.

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

Ans: Copper is a better conductor of heat than the stainless steel.