NCERT Solutions for Class 7th Science
Chapter 4 - HEAT
(Complete Downloadable Chapter Solution PDF file is at the bottom of the page)
Q.1 State similarities and differences between the laboratory thermometer and the clinical thermometer.
Ans Similarities:
1) Both the thermometer consists of a long, narrow, uniform glass tube with a bulb at one end.
2) Both thermometer uses mercury for measuring temperature.
Differences:
1) Clinical thermometer is used to measure temperature of human beings only whereas laboratory thermometer is used to measure temperature of other objects in laboratories.
2) Clinical thermometer measures temperature from 35°C to 42°C whereas laboratory thermometer measures temperature from -10°C to 110°C.
3) A clinical thermometer can be tilted while taking reading whereas laboratory thermometer should be kept upright.
Q.2 Give two examples each of conductors and insulators of heat.
Ans Conductors: Iron and Copper
Insulators: Plastic and wood
Q.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 (a) The hotness of an object is determined by its temperature.
(b) Temperature of boiling water cannot be measured by a clinical thermometer.
Q.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
Q.5 Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.
Q.6 Look at Fig. 4.13. Mark where the heat is being transferred by conduction, by convection and by radiation.
Q.7 In places of hot climate it is advised that the outer walls of houses be painted white. Explain.
Q.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
Q.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.
Q.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.
Q.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.