NCERT Solutions for Class 7 Science - Heat

Exercises

Q1. State similarities and differences between the laboratory thermometer and the clinical thermometer.
Ans:

Clinical and Laboratory Thermometer

Q2. Give two examples each of conductors and insulators of heat.
Ans:
(i) Examples of conductors: Iron, copper
(ii) Examples of insulator: Wood, plastic

Q3. Fill in the blanks:
(a) The hotness of an object is determined by its ________.
Ans: Temperature.

(b) Temperature of boiling water cannot be measured by a ________ thermometer.
Ans: Clinical Thermometer

(c) Temperature is measured in degree ________.
Ans: Celsius

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

(e) A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of ________.
Ans: Conduction.

(f) Clothes of ________colours absorb heat better than clothes of light colours.
Ans: Dark

Q4. Match the following:

Ans: 

Q5. Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing?
Ans: By wearing more layers of clothing, air gets trapped between different layers. As air is a bad conductor of heat, it does not allow the escape of the heat from the body. On the other hand, wearing just one piece of clothing creates just one insulator layer and is less effective in beating the cold.

Q6. Look at Fig. (in NCERT Text Book). Mark where the heat is being transferred by conduction, by convection and by radiation.
Ans:

Q7. In places of hot climate it is advised that the outer walls of houses be painted white. Explain.
Ans: White colour reflects most of the heat falling on it. This makes the house colder. Thus, in places of hot climate, it is advised that the outer walls of the house be painted white.

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
Ans: (d)
Explanation: The temperature of the mixture will be between 30°C and 50°C because hot water loses heat and simultaneously cold water gains heat. This keeps the temperature 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.
Ans: (b)
Explanation: It does not flow from iron ball to water or from water to iron ball because both of them have the same temperature of 40°C. 

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.
Ans: (d)
Explanation: It does not become cold because wood is a bad conductor of heat 

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 stainless steel.
(d) copper is easier to clean than stainless steel.
Ans: (c)
Explanation: Copper is a better conductor of heat than stainless steel.