CBSE · NCERT · Class 7 Science · Chapter 3

NCERT Solutions: Class 7 Science Chapter 3 - Heat

11 textbook Q&A11 verifiedFree Content

Chapter-wise NCERT intext questions and exercise answers for Heat, grounded in the official textbook.

Questions are taken verbatim from the NCERT textbook; answers were grounded against the chapter's content during generation. Items needing review are marked.
Sections in this chapter
Exercises 11
Your Progress - Chapter 30% complete
1Exercises11 questions
Q.1State similarities and differences between the laboratory thermometer and the clinical thermometer.v
Answer:

Similarity: both thermometers measure temperature and have a glass tube with a liquid column. Differences: a clinical thermometer has a narrow range, usually 35 °C to 42 °C, and has a kink to hold the mercury level for reading body temperature. A laboratory thermometer has a wider range, commonly -10 °C to 110 °C, and has no kink, so it must be read while it is still in contact with the object.

✓ Verified and validated
Q.2Give two examples each of conductors and insulators of heat.v
Answer:

Conductors of heat: copper and aluminium. Insulators of heat: wood and plastic.

✓ Verified and validated
Q.3Fill 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.v
Answer:

(a) temperature
(b) clinical
(c) Celsius
(d) radiation
(e) conduction
(f) dark

✓ Verified and validated
Q.4Match the following: Column I: Land breeze blows during, Sea breeze blows during, Dark coloured clothes are preferred during, Light coloured clothes are preferred during. Column II: Summer, Winter, Day, Night.v
Answer:

Land breeze blows during - Night; Sea breeze blows during - Day; Dark coloured clothes are preferred during - Winter; Light coloured clothes are preferred during - Summer.

✓ Verified and validated
Q.5Discuss why wearing more layers of clothing during winter keeps us warmer than wearing just one thick piece of clothing.v
Answer:

More layers of clothing trap air between them. Air is a poor conductor of heat, so these trapped air layers reduce heat loss from the body and keep us warmer than a single thick piece of clothing.

✓ Verified and validated
Q.6Look at Fig. 3.13. Mark where the heat is being transferred by conduction, by convection and by radiation. The figure shows water boiling in a metal pan kept on a burner flame, with a metal handle attached to the pan.v
Solution

Identify conduction in solids, convection in liquids/gases and radiation from the flame without direct contact.

Answer:

Mark conduction in the metal pan and along its metal handle. Mark convection in the water inside the pan, where hot water rises and cooler water sinks. Mark radiation from the burner flame to the pan and to nearby surroundings.

✓ Verified and validated
Q.7In places of hot climate it is advised that the outer walls of houses be painted white. Explain.v
Answer:

White surfaces reflect most of the heat radiation falling on them and absorb less heat. Painting outer walls white keeps the house cooler in hot climates.

✓ Verified and validated
Q.8One 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 °Cv
  1. a. 80 °C
  2. b. more than 50 °C but less than 80 °C
  3. c. 20 °C
  4. d. between 30 °C and 50 °C
Solution

When equal amounts of water at different temperatures are mixed, heat flows from the hotter water to the colder water until an intermediate temperature is reached.

Answer:

(d) between 30 °C and 50 °C

✓ Verified and validated
Q.9An 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.v
  1. a. flow from iron ball to water
  2. b. not flow from iron ball to water or from water to iron ball
  3. c. flow from water to iron ball
  4. d. increase the temperature of both
Solution

Heat flows only when there is a temperature difference. Since both are at 40 °C, there is no net heat flow.

Answer:

(b) not flow from iron ball to water or from water to iron ball.

✓ Verified and validated
Q.10A 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.v
  1. a. becomes cold by the process of conduction
  2. b. becomes cold by the process of convection
  3. c. becomes cold by the process of radiation
  4. d. does not become cold
Solution

Wood is a poor conductor of heat, so the coldness is not conducted effectively to the other end.

Answer:

(d) does not become cold.

✓ Verified and validated
Q.11Stainless 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.v
  1. a. copper bottom makes the pan more durable
  2. b. such pans appear colourful
  3. c. copper is a better conductor of heat than the stainless steel
  4. d. copper is easier to clean than the stainless steel
Solution

Copper conducts heat well, so it helps the pan heat quickly and evenly.

Answer:

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

✓ Verified and validated
Back: Ch.2
Next: Ch.4