Evaporation is the process in which a liquid state of matter (water) is converted into a gaseous state of matter (vapour). In general terms, evaporation is defined as the process in which the liquid state is converted into gas. This process requires heat energy.
Examples of Evaporation
- Drying of clothes
Factors That Affect the Evaporation
- Temperature: As the temperature increases, the rate of evaporation also increases. Temperature and rate of evaporation are proportional to each other.
- Surface area: As the surface area increases, the rate of evaporation increases. The surface area and rate of evaporation are proportional to each other.
- Humidity: The rate of evaporation decreases with an increase in humidity. Humidity and the rate of evaporation are inversely proportional to each other.
- Wind speed: Increase in wind speed results in increased evaporation. Wind speed and rate of evaporation are proportional to each other.
Evaporation Causes Cooling
Evaporation causes cooling is the general process. The principle involved here is the matter must either gain or lose energy to change its state. Here, molecules move from liquid to gaseous state and so it needs potential energy and kinetic energy. Due to this, energy transfer occurs in the surroundings as well and this is transferred from substance to surroundings or vice versa. The change in temperature until the evaporation process will lead to cooling. Hence, evaporation causes a cooling effect. When a liquid evaporates, the particles of the liquid absorb energy from the surroundings to compensate for the loss of energy during evaporation. Since evaporation causes cooling, this makes the surroundings cool.
- An earthen pot or a Matka is porous in nature. Water placed in earthen pots is evaporated from minuscule pores it has as it is made of mud particles. This evaporation of water produces a cooling effect. Some of the heat energy that is generated is used in the process of evaporation. Hence, water stored in earthen pots tends to become cooler in summer.
- In a desert cooler, the water inside it is made to evaporate. This leads to the absorption of energy from the surroundings, thereby cooling the surroundings. Evaporation depends on the amount of water vapour present in the air (humidity). If the amount of water vapour present in the air is less, then evaporation is more. On a hot dry day, the amount of water vapour present in the air is less. Thus, water present inside the desert cooler evaporates more, thereby cooling the surroundings more. That is why a desert cooler cools better on a hot dry day.