Question

Methanol is used for cleaning paint brushes. A painter notices that when she spills some methanol onto the back of her hand the methanol dries up quickly. While her hand is drying it feels cold. Explain how the evaporating methanol cools down her hand.

When water is spilled on a table, it is found that the water will dry more quickly if it is spread over a large area. Explain why this is so.

How would you expect the rate of cooling of a hot drink in a cup with a large diameter compared with the rate of cooling in a cup with a small diameter?

Answer 1

Answer:

1st answer:

You should always remember the fact that , materials in a liquid state take up specific latent heat and get converted to gas.

In this case also, the methanol takes up the latent heat of evaporation from the surface of the body and undergoes change in state.

Since heat is taken away from the body, the skin feels cold.

2nd answer:

You should again remember the fact that evaporation is a surface phenomenon mediated by the free surface molecules.

Now higher the surface area, more is the evaporation.

Hence, rate of cooling of hot drink in a large diameter cup will be faster as compared to smaller diameter cup.