Q1.
Place a small damp cloth in the Sun. Keep another damp cloth in the shade. Which one do you think will dry first? Why?
Answer
The cloth in the Sun dries first. It dries faster because sunlight gives heat, and heat turns the water in the cloth into water vapour more quickly.
How to test it:
- Take two pieces of the same cloth, of the same size.
- Dip both in water and squeeze both the same amount.
- Spread one in bright sunlight and one in the shade, at the same time.
- Touch both after 15 minutes, then after 30 minutes.
| Time | Cloth in the Sun | Cloth in the shade |
|---|---|---|
| After 15 minutes | Only slightly damp | Still clearly wet |
| After 30 minutes | Dry, and warm to touch | Still damp in the middle |
Why it happens: To dry, the water in the cloth must leave it as an invisible gas called water vapour. Heat helps the water do that. Sunlight brings heat, so the water in the sunlit cloth turns into vapour quickly and goes into the air. The cloth in the shade gets very little heat, so its water leaves slowly. A breeze helps too — it carries the vapour away and lets more water leave.
Where you have seen this: clothes on the line dry fastest on a hot, windy afternoon. Papads and mango slices are put out in the Sun to dry. Salt is made by letting sea water dry in the Sun. All of it is free energy from the Sun, and no plug is needed.