Question

Why do we wear cotton clothes in summer?
A. Cotton is a bad conductor of heat and doesn’t allow passage of warmer air near body
B. Cotton is a good conductor of heat and allows body heat to escape in the atmosphere
C. Cotton absorbs sweat from the body, exposing it to atmosphere for easy evaporation
D. None of the above

Answer 1

Hint: We need to check the realities behind every possibility that is given. After eliminating the wrong options, we will find the right answer. We will also need to know some properties of cotton to get the answer.

Formula used: $ H=m \times L $

Complete step-by-step solution:
First of all, we need to know two important properties of cotton.
1. It is porous. It means there are a lot of holes or free space inside the structure of cotton.
2. It’s usually a good insulation for heat. It means, cotton doesn’t conduct heat. It’s because air is a bad conductor of heat and cotton is basically filled with air (usually).
Now, here we have to remember that, cotton acts as the best insulation of heat when it’s filled with air. But in summer, our body produces a lot of sweat. So, the holes in cotton clothes will be partially filled with water. And, the insulation property of cotton is of no great help.
On the other hand, when sweat enters the whole, it gets access to the atmospheric air. And air fastens the process of evaporation of sweat (or any other liquid). Evaporation takes a lot of heat from the surrounding i.e. from the body. Hence the body is cooled.
If m gm of sweat be evaporated, the heat taken is,
$H=m \times L $
L is called the latent heat of vaporization.
So, option C is the correct answer.

Additional information:
We wear woolen clothes in winter because it's a good insulator for heat.

Note: In this problem, it’s easy to think that the insulation of cotton may be the answer. But this is not the case. You have to consider other reasons as well. In this way, we saw that evaporation of sweat played a much important role here.