Question

Which of the following applications illustrates that evaporation leads to cooling?
A) Perspiration in human body
B) Transpiration in leaves
C) Water in earthen pot
D) All of the above

Answer 1

Hint: Evaporation is defined as the loss of water in the form of water vapour. The evaporation process requires energy in the form of heat to convert liquid into the vapour state. An example of evaporation is drying of clothes under sunlight.

Complete answer:
Evaporation is one of the most common phenomena taking place in our surroundings. It requires energy for conversion of the liquid into gaseous state. One of the greatest significance of evaporation is it causes cooling. The heat energy is taken away by the water molecules to convert it into gases and it escapes. As the heat is taken from the system. It causes the cooling effect in it due to heat loss. Few examples in our daily life that are given in the question -

Perspiration in the human body- perspiration means sweating. Our body releases water through the minute pores present on the skin. This water molecule under the effect of sun/heat is converted into gas for which it absorbs energy in the form of heat from the body. Thus, the loss of heat from the body causes cooling.

Transpiration in the leaves- Transpiration is the process by which the water is lost in the form of water vapour through the stomata. As the water absorbs heat and changes into vapour, it causes a cooling effect.

Water in earthen pots- The earthen pots have minute pores through which the water vapour can escape in the presence of heat. The water inside converts into the vapour or gas and escapes through the pores by absorbing heat. This loss of heat causes a cooling effect.

So we can say that all the above three processes cause cooling. The correct answer is D.

Note: Transpiration is also important for uptake of water and minerals from the soil. The sweat is released by the sweat glands present in the skin. They along with the water release excess salts like sodium chloride, urea, sugar, ammonia.