NCERT Solutions Curiosity Chapter 7 .2 Convection — In-text Questions

Book page 937 Updated on2026-09-05

Q1.

You observed that the cup under which the candle was placed, rises up (Fig. 7.3b). Why is it so?

Answer

Because the air inside that cup becomes hot, expands and turns lighter, and rising hot air lifts the cup.

Candle flame heats the air around it
Air inside the cup warms up
Warm air expands → occupies more space
Same air in a bigger space → becomes lighter
⇒ it rises up and the cup goes up

Try This: place a partially inflated balloon in the Sun (Fig. 7.4). After some time the air inside gets heated, expands, and the balloon becomes visibly larger — the same expansion, made easy to see.

Q2.

How does heat transfer take place in liquids? Do liquids also rise up when heated like air?

Answer

Heat travels through liquids mainly by convection — and yes, a liquid also rises when it is heated, exactly as air does.

Water at the bottom gets heated
It expands → becomes lighter → rises
Cooler, heavier water at the sides comes down to take its place
This water is heated in turn and also rises
⇒ a convection current is set up until all the water is hot

Why it happens: unlike a solid, the particles of a liquid can move about freely. So they do not merely pass heat to their neighbours — they carry the heat with them from one place to another. That is the whole difference between conduction and convection.

Check it yourself: Activity 7.3, with a grain of potassium permanganate at the bottom of a beaker, makes this invisible current visible as a coloured streak.

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