NCERT Solutions Class 7 Science Chapter 4 Heat

NCERT Solutions for Class 7 Science Chapter 4 Heat

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

Ans. 1 - Similarities between clinical and laboratory thermometers are as follows:

1. Both of them are used for measuring temperature.
2. Both of them use mercury as an indicator for rise and fall in temperature.

Differences between clinical and laboratory thermometers are as follows:

1. Clinical thermometer is used to measure body temperature whereas; laboratory thermometer is used to measure temperature of substances.
2. The range of clinical thermometer is from 35°C to 42°C while that of laboratory thermometer is from minus 10°C to 110°C.

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

Ans. 2 The examples of conductors of heat are as follows:

1. Aluminium
2. Copper

The examples of insulators of heat are as follows:

1. Wood
2. Rubber

Question - 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. It transfers heat to its other end by the process of .

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

Ans. 3

(a) Temperature
(b) Clinical
(c) Celsius
(d) Radiation
(e) Conduction
(f) dark

Question - 4 Match the following:
 

Ans.4 The correctly matched contents of the two given columns are as follows:

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

Ans.5 Wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing because in between the multiple layers of clothing, air is trapped that prevents the loss of heat from the body to the surroundings. Air is a poor conductor of heat and prevents the transfer of heat from one region to the other. This trapped air in between the layers of clothing keeps us warmer than the single thick clothing.

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

Ans. 6 Various modes of transfer of the heat in the given diagram can be shown as follows:

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

Ans.7 The outer walls are advised to be painted white in hot climate conditions because white colour reflects maximum amount of heat back into the surroundings, that falls on it. Therefore, white coloured walls absorb least amount of heat and keep the house cool.

Question - 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. 8
(d) between 30°C and 50°C.

Question - 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.9 (a) flow from iron ball to water.

Question - 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.

Ans. 10 (d) does not become cold.

Question - 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. 11 (c) copper is a better conductor of heat than the stainless steel.