Solution of Chapter 4. Heat (NCERT Science Book)

State few similarities and differences between the laboratory thermometer and the clinical thermometer.

Give any two examples each of conductors and insulators of heat.

Fill in the blanks:

a. The hotness of an object is determined by its _____.

b. Temperature of boiling water cannot be measured by _______ 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.

Match the following:

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

Look at Fig. 4.13. Mark where the heat is being transferred by

conduction, by convection and by radiation.

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

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

An iron ball at 40⁰C is dropped in a mug containing water at 40⁰C. 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.

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.

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.

Go to a doctor or your nearest health centre. Observe the doctor taking temperature of patients. Enquire:

a. why she dips the thermometer in a liquid before use.

b. whey the thermometer is kept under the tongue.

c. whether the body temperature can be measured by keeping the thermometer at some place other than the mouth.

d. whether the temperature of different parts of the body is the same or different.

You can add more questions which come to your mind.

Go to a veterinary doctor (a doctor treats animals). Discuss and find out the normal temperature of domestic animals and birds.

Wrap a thin paper strip tightly around an iron rod. Try to burn the paper with candle while rotating the iron rod continuously. Does it burn? Explain your observation.

Take a sheet of paper. Draw a spiral on it as shown in the Fig. 4.14. Cut out the paper along the line. Suspend the paper as shown in Fig. 4.14 above a lighted candle. Observe what happens. Think of an explanation.

Take two similar transparent glasses of bottles having wide mouths. Put a few crystals of potassium permanganate or pour a few drops of ink in the bottle. Fill this bottle with hot water. Fill the other bottle with cold water. Cover the cold water bottle with a thick piece of paper such as a post card. Press the post card firmly with one hand and hold the bottle with the other hand. Invert the bottle and place it on top of the hot water bottle. Hold both the bottles firmly. Ask some other person to pull the post card. Observe what happens. Explain.