# Heat

## NCERT Solution

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

Differences
Clinical ThermometerLaboratory Thermometer
The range of clinical thermometer is from 35°C to 42°C or from 94°F to 108°F.The range of laboratory thermometer is from -10°C to 110°C.
Mercury level does not fall on its own, as there is a kink near the bulb to prevent the fall of mercury level.Mercury level falls on its own as no kink is present.
Temperature can be read after removing the thermometer from armpit or mouth.Temperature is read while keeping the thermometer in the source of temperature, e.g. a liquid or any other thing.
To lower the mercury level jerks are given.No need to give jerk to lower the mercury level.
It is used for taking the body temperature.It is used to take temperature in laboratory.

#### Similarities:

• Both are made of glass tube.
• Both are filled with mercury.
• Both are generally graduated on Celsius scale.

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

Answer: Examples of conductor: Iron, copper

Examples of insulator: Rubber, plastic

Question 3: Fill in the blanks:

1. The hotness of an object is determined by its __________.
2. Temperature of boiling water cannot be measured by a _____________ thermometer.
3. Temperature is measured in degree ______________.
4. No medium is required for transfer of heat by the process of __________.
5. A cold steel spoon is dipped in a cup of hot milk. It transfers heat to its other end by the process of ______________.
6. Clothes of ______________ colours absorb heat better than clothes of light colours.

Answer: (a) temperature, (b) clinical thermometer Dark, (c) Celsius, (d) Radiation, (e) Conduction, (f) dark

Question: 4 - Match the following:

Column AColumn B
(1) Land breeze blows during(a) Summer
(2) Sea breeze blows during(b) Winter
(3) Dark coloured clothes are preferred during(c) Day
(4) Light coloured clothes are preferred during(d) Night

Answer: (1) d, (2) c, (3) b, (4) a

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

Answer: By wearing more layers of clothing, air gets trapped between different layers. This makes different layers of insulation and thus provides better protection against cold. On the other hand, wearing just one piece of clothing creates just one insulator layer and hence is less effective in beating the cold.

Question 6: Look at Fig. 4.13 (in NCERT Text Book). Mark where the heat is being transferred by conduction, by convection and by radiation.

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

Answer: 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 house be painted white.

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

1. 80°C
2. more than 50°C but less than 80°C
3. 20°C
4. between 30°C and 50°C

Answer: (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

1. flow from iron ball to water.
2. not flow from iron ball to water or from water to iron ball.
3. flow from water to iron ball.
4. increase the temperature of both.

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

Question 10: A wooden spoon is dipped in a cup of ice cream. Its other end

1. becomes cold by the process of conduction.
2. becomes cold by the process of convection.
3. becomes cold by the process of radiation.
4. does not become cold.

Answer: (d) does not become cold.

Question: 11: Stainless steel pans are usually provided with copper bottoms. The reason for this could be that

1. copper bottom makes the pan more durable.
2. such pans appear colourful.
3. copper is a better conductor of heat than the stainless steel.
4. copper is easier to clean than the stainless steel.

Answer: (c) Copper is a better conductor of heat than the stainless steel.