1.8- Evaporation.
We have seen that how small amount of liquid gets dried up or vaporized without actually applying any heat e.g.- liquids in the wet clothes or small patches of water on the ground. The liquid has higher kinetic energy and its particles are able to break away and convert into vapour. The phenomenon of change of a liquid into vapours at any temperature below its boiling point is known as evaporation.
1.8.1- Factors that affect evaporation.
The rate of evaporation gets affected by the following factors:-
- Increasing the surface area:On increasing surface area, rate of evaporation increases. For instance, spreading out wet clothes before drying them makes them to dry faster.
- Increasing the temperature: Increasing temperature provides more kinetic energy to the particles of liquid for faster evaporation.
- Decreasing the humidity: If the humidity or amount of water vapour in our atmosphere is already high, the rate of evaporation would slow down or decrease.
- Increasing wind speed: With increasing wind speed, the water vapour particles move away with the wind decreasing the amount of water vapour in the surrounding and thus evaporations becomes faster.
1.8.2- Cooling effect of evaporation.
The process of evaporation also has some cooling effect which can be observed in many ways. For instance, in an open vessel, the particles of liquid keep evaporating and absorbing energy from the surrounding to regain the lost energy from the surrounding that was lost during evaporation. This absorption from the surroundings makes the surroundings cool.
Another example showing the effect of cooling of evaporation is when we pour some acetone (nail polish remover) on our hand or palm, we feel cool because of the evaporation. Yet another example of this effect is the sprinkling of water on the roofs and grounds that will vaporise and make the surroundings cool.
Also, there are some more points that you must look at:
- Wearing cotton clothes in the summer season:People wear cotton clothes in summer because cotton is a good absorber of water and helps in absorbing the sweat and exposing it to the atmosphere for easy evaporation and thus provide cooling.
- A glass containing ice-cold water has water droplets on its outer surface: The water vapour that is present in the air, on coming in contact with the cold surface of the glass containing ice-cold water loses its energy and gets converted into the liquid state, which is visible in the form of water droplets on the outer surface of the glass.
