EVAPORATION

  • In liquids, a small fraction of particles at the surface, having higher kinetic energy, is able to break away from the forces of attraction of other particles and gets converted into vapour. This phenomenon of change of a liquid into vapours at any temperature below its boiling point is called evaporation.

1.Factors affecting evaporation

  • The rate of evaporation increases with
  • increase of surface area
  • increase of temperature
  • decrease in humidity
  • increase in wind speed

1. How does evaporation cause cooling?

The particles of liquid absorb energy from the surrounding to regain the energy lost during evaporation. This absorption of energy from the surroundings makes the surroundings cold.

-Why should we wear cotton clothes in summer?

* During summer, we perspire more because of the mechanism of our body which keeps us cool. We know that during evaporation, the particles at the surface of the liquid gain energy from the surroundings or body surface and change into vapour. The heat energy equal to the latent heat of vaporisation is absorbed from the body leaving the body cool. Cotton, being a good absorber of water helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation.

-Why do we see water droplets on the outer surface of a glass containing ice-cold water?

* If we take some ice-cold water in a tumbler. Soon water droplets forms on the outer surface of the tumbler. The water vapour present in air, on coming in contact with the cold glass of water, loses energy and gets converted to liquid state, which we see as water droplets.