Question

Evaporation causes
(A) Cooling
(B) Heating effect
(C) An increase in weight
(D) An increase in density

Answer 1

Evaporation is a surface phenomenon. It can be seen in daily activities. The process of evaporation is very useful in many activities like drying, production of salt, etc.

Complete step by step solution:

To answer this question first we should know what the definition of evaporation is.
Evaporation is the process of conversion of a liquid into its gaseous form. It is a surface phenomenon which means that only surface molecules take part in the process of evaporation.
In evaporation, the molecules of the liquid absorb energy from the surroundings and increase their internal energy. These high energy molecules then start colliding more frequently and try to leave the surface of the liquid. While low energy molecules remain inside the liquid.
Since, the molecules absorb energy from the surrounding and also leave the liquid, evaporation causes a cooling effect.
This property of evaporation is used in natural cooling of water. Water is kept in earthen pots, these pots have tiny pore through which high energy water molecules escape leaving the water cool inside the pot.
When water molecules leave the liquid then the volume of the liquid also decreases. The density of a substance is inversely proportional of volume, so when volume of water decreases then the density increases.
Therefore, evaporation causes cooling and increase in density.
Hence, the answers for the given question are option (A) and (D).

Note: Students can confuse evaporation with transpiration. Transpiration is a biological phenomenon. It is similar to evaporation but it happens on leaf surfaces. In transpiration the water is lost from the stomata of the leaf by the process of evaporation. The rate of transpiration is maximum during the day.