NCERT Solutions Curiosity Chapter 7 .3 Radiation — In-text Questions

Book page 967 Updated on2026-09-05

Q1.

I wonder how heat from the fire reaches us?

Answer

The heat of the fire reaches us by radiation — it travels directly from the hot object (the fire) to us, and no medium is needed for this transfer.

Process	How heat moves	Medium needed?	Example here
Conduction	Particle passes heat to its neighbour; particles stay in place	Yes	Flame → metal pan
Convection	Heated particles themselves move from place to place	Yes	Smoke and hot air rising from the fire
Radiation	Heat travels straight from the hot object to us	No	Warmth felt by Pema and Palden facing the fire

Why it must be radiation: the hot air of the fire rises straight up, so convection cannot bring warmth sideways to the children's faces. Nor are they touching the fire, so conduction is ruled out. The warmth reaches them directly across the gap — that is radiation. The heat of the Sun reaches the Earth in the very same way, crossing empty space where there are no particles at all.

Q2.

You must have observed that a hot utensil kept away from the flame cools down after some time. What is the reason for it?

Answer

The hot utensil cools down by radiating heat to its surroundings.

Why it happens: all objects radiate heat. An object that is hotter than its surroundings gives out more heat than it receives, so its temperature falls until it becomes as warm as the room. The hot utensil keeps sending out heat to the cooler air, walls and table around it, and cools down. (Some heat also leaves by conduction into the platform it rests on and by convection into the air above it, but the utensil would cool down by radiation alone.)

Did you know? The exchange works both ways. A cold glass of water kept in a warm room gains heat by radiation from its surroundings and slowly becomes warm.

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