Q1.
Sun-powered Water Warmer — 1. Fill two cups with water. 2. Place one cup in the sunlight and another in the shade. 3. Wait for 15 – 20 minutes and then touch the water in both the cups. What do you notice?
Answer
What you will notice: the water in the cup kept in the sunlight feels clearly warm. The water in the cup kept in the shade still feels cool. Both cups had the same water at the start, so the Sun must have done the warming.
How to do it properly:
- Take two cups of the same size and the same colour.
- Fill both with the same amount of water from the same pot, at the same time.
- Put one cup in bright sunlight — a sunny windowsill or the school ground.
- Put the other in the shade, close by, so the air around both is the same.
- Wait 15 to 20 minutes. Do not move them.
- Now dip a finger in each cup, one after the other, and compare.
| Cup | Where it was kept | How the water feels after 20 minutes |
|---|---|---|
| Cup 1 | In the sunlight | Warm — clearly warmer than when you poured it |
| Cup 2 | In the shade | Still cool — almost the same as at the start |
Why it happens: Sunlight is not just light. It carries heat energy as well. When sunlight falls on the cup and the water, that heat passes into the water and the water gets warm. The cup in the shade gets no sunlight, so nothing warms it. As the book says — this shows how the sunlight gives us heat energy.
Where you have already seen this: water in a black tank on a roof turns hot by afternoon; a solar water heater on a roof gives hot water without any gas or electricity; and a solar cooker cooks dal using only the Sun. Do you know? The Bhadla Solar Park in Rajasthan is one of the largest solar power plants in the world.