# NCERT Solutions for Class 7 Science Chapter 4

## Heat Class 7

### Exercise : Solutions of Questions on Page Number : 45

Q1 :

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

Similarities:

(i) Both clinical and laboratory thermometers have long, narrow, uniform glass tubes.

(ii) The bulbs of both the thermometers have mercury in them.

Differences:

(i) The temperature range of clinical thermometers is from 35°C to 42°C while that of laboratory thermometer is from -10°C to 110°C.

(ii) Clinical thermometer is used to measure the temperature of a human body. However, laboratory thermometer cannot be used to measure the temperature of a human body.

(iii) The least count of both the thermometers differs.

(iv) Unlike clinical thermometer that can be tilted, laboratory thermometer is kept upright while reading the temperature values.

Q2 :

Give two examples each of conductors and insulators of heat.

Two examples of conductors of heatare:

(i) Aluminium

(ii) Iron

Two examples of insulators of heat are:

(i) Wood

(ii) Plastic

Q3 :

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. It transfers heat to its other end by the process of __ _ _.

(f) Clothes of ___ _ colours absorb heat better than clothes of light colours.

Q4 :

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

Q5 :

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

Q6 :

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

Q7 :

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

Q8 :

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

Q9 :

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.

Q10 :

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.

Q11 :

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.