NCERT solutions for Science [English] Class 7 chapter 3 - Heat [Latest edition]

State similarities between the laboratory thermometer and the clinical thermometer.

State differences between the laboratory thermometer and the clinical thermometer.

Give two examples each of conductors and insulators of heat.

The hotness of an object is determined by its ______.

Temperature of boiling water cannot be measured by a ______ thermometer.

Temperature is measured in degree ______.

No medium is required for transfer of heat by the process of ______.

A cold steel spoon is dipped in a cup of hot milk. Heat is transferred to its other end by the process of ______.

Clothes of ______ colours absorb more heat better than clothes of light colours.

Match the following:

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

Look at Figure. 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 ______.

An iron ball at 40°C is dropped in a mug containing water at 40°C.

The heat will ______.

A wooden spoon is dipped in a cup of ice cream. Its other end ______.

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

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

1. Why she dips the thermometer in a liquid before use.
2. Why the thermometer is kept under the tongue.
3. Whether the body temperature can be measured by keeping the thermometer at some place other than the mouth.
4. 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 who 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 Figure. Cut out the paper along the line. Suspend the paper as shown in Figure above a lighted candle. Observe what happens. Think of an explanation.

Take two similar transparent glass bottles having wide mouths. Put a few crystals of potassium permanganate or pour a few drops of ink in one 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 postcard. Press the postcard 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 postcard. Observe what happens. Explain.