Question

The rate of evaporation decreases with an increase in____________.
a.) Humidity
b.) Temperature
c.) Wind speed
d.) Surface area

Answer 1

Hint: We should carefully observe the options. We have to relate each option with our day to day life. Temperature, wind speed and surface area can easily be related but humidity is the amount of water vapour present in the air.

Complete step-by-step answer:
In simple words, we will now understand about evaporation. Evaporation is the conversion of liquid into gas. A simple example is if we boil water continuously, all the water will convert into water vapour.
Now, to answer our question let us study each and every option. Rate of evaporation is the time taken by liquid to convert into gas phase. It depends on many factors. These factors are explained below:
Temperature: By taking an example we will understand this. If we want to boil water, we know that if we provide maximum heat then only it will take less time to boil water. Or we can say that we put our wet clothes on a sunny day because we know that clothes will dry faster in high temperatures.
Humidity: So, let us think about the holding capacity of us. How many books can you hold in your hands? It might be five books, ten books. There is a limit for each of us. We can only hold books according to our capacity. We can store data in a computer according to its storage capacity. Same is for air. Humidity is the amount of water vapour present in air. Or we can say that the water holding capacity of air is humidity. If we are saying that air humidity is high, then the amount of water vapour is high in air. So, now water vapour intake capacity of air is decreased. But evaporation is the process by which extra water vapour is added to the atmosphere. So, naturally with more humidity the evaporation rate decreases. Humid air adds an extra pressure on water reservoirs, which in turn helps the surface molecules of the reservoirs to stay in contact with the rest of the molecules.
Wind speed: We should know that Evaporation increases with the increase in wind speed. Vapour particles move away when the speed of wind increases. This leads to an increase in the amount of water vapour in the atmosphere.
Surface area: We should know that substance which has a larger surface area will evaporate faster, as there are more surface molecules per unit of volume that are potentially able to escape.
So, from the above points we discuss we came to know that if we increase temperature, wind speed and surface it will increase evaporation. And increase in humidity will decrease the rate of evaporation. The answer to this question is option A.

Note: We should note that the rate of evaporation at a given place is always dependent on the humidity of that place because if the air is already filled with water vapour, it will not have any place to hold excess vapour and therefore, evaporation will occur at an extremely slow rate.
Let us consider an example. If we take two wet cloths and hang one cloth in ample sunlight while the other in a shaded area, which one of the two will dry faster? It will be the one that is in the sunlight because the air in that area is hot and the humidity is low. It will have more capacity to hold water vapour and thus the rate of evaporation will be faster. On the other hand, the cloth in the shaded area is surrounded by air that is cooler. As cold air has less capacity to hold water vapour than hot air, the rate of evaporation of water from the wet cloth will be slower too.