Evaporation
Topic: Water in the Atmosphere: Humidity, Condensation, Clouds and Precipitation · NCERT: Class 11, Ch 10 "Water in the Atmosphere"; Class 11, Ch 12 "Water (Oceans)"
Meaning
Evaporation is the change of water from liquid into vapour. Heat is its main cause. It is faster when the air is:
- warm, because warm air can hold more vapour;
- dry, because dry air has room for more moisture;
- moving, because wind carries away the damp layer over the water and brings in drier air.
Evaporation takes in latent heat (hidden heat stored in the vapour), so it cools the surface it leaves. It is highest over subtropical oceans under the trade winds.
Example
An earthen pot (matka) in an Indian home keeps water cool in summer. Water seeps through tiny pores to the outside and evaporates, and this takes heat away from the water inside.
Don't confuse with
- Transpiration: this is vapour released by plants through tiny pores in their leaves. Evaporation is from open water, soil and other surfaces.