Evaporation Process :
Evaporation is the process in which a liquid changes to gaseous state at the free surface, below the boiling point through the transfer of heat energy.
The net escape of water molecules from the water surface from liquid to gaseous state constitutes evaporation.
How the Evaporation is caused :
Consider a water body in a pond. The molecules of water are in a constant motion with different velocity ranges. When some heat is added to the water body then the velocity range and the average velocity will increase. When some molecules will possess sufficient kinetic energy, they may come over the water surface.
Similarly, the atmosphere in the neighborhood of the water surface also contains water molecules. Some of them may loses energy and penetrate the water surface. The net escape of water molecules from the water body from the liquid state to the gaseous state constitutes the Evaporation.