What is Evaporation
It is the phenomena of change of liquid into water vapour
Example 1
-
When we put
wet clothes on the terrace
,
it gets dried up
This is because the water in clothes gets evaporated due to the
heat rays of the sun
Example 2
-
If we
boil water,
its quantity decreases after some time
This is because water in the bowl gets evaporated due to heat of flame
What causes Evaporation?
- We know that liquids like water are made up of a number of molecules
- All these molecules have a different level of kinetic energy in them
- Those molecules at surface have higher level of kinetic energy move away from other molecules and
- This energy is more than force of attraction binding different molecules
- This causes water to get converted into water vapour and cause evaporation
Different Factors Affecting Evaporation
- Temperature: As the temperature increases, the rate of evaporation also increases.
- Surface area: As the surface area increases, the rate of evaporation increases.
- Humidity: The rate of evaporation decreases with an increase in humidity.
- Wind speed: As the wind speed increases, the rate of evaporation increases.
Let's look at them one by one
Increase in Temperature
More the temperature, more the level of evaporation
(Clothes dry up faster in summers rather than winters due to high temperature)
It is because due to higher temperature, molecules of water achieve higher kinetic energy
This makes them move away and get converted into water vapour
Increase in Surface Area
More the surface area, more the evaporation
When we dry our clothes, we spread them instead of folding them
This is to increase the surface area so that more heat from the sun can reach the clothes and clothes dry faster
Increase in Wind Speed
More the wind speed, more the evaporation
This is because due to higher winds, molecules of water obtain more kinetic energy
This makes them move away from other water molecules and evaporate faster
Decrease in Humidity
Humidity is the amount of water vapour present in air
When the level of humidity is high, evaporation is low
This is because air already has such a high amount of water vapour. It is not able to hold more water vapour due to evaporation
How does Evaporation Cause Cooling?
We know that evaporation is a process in which Liquid gets converted into gas
In this process, liquid absorbs energy from surroundings
This makes surroundings cool
Example 1
On a hot day, people sprinkle water on roof
This causes the roof to cool
This is because water sprinkled gets converted into water vapour
During its process, energy is used from surroundings (roof in this case) causing roof to become cool
Example 2
When we pour some acetone (nail polish remover) on our palm
We feel cool
This is because when acetone evaporates (convert into vapour)
It uses heat from surroundings (palm in our case)
This causes our palm to feel cool
Example 3
Sweating help us to cool
Sweating helps to maintain our body temperature and cool us down
In summers, when we feel heat. Liquid from our body comes out as sweat
It gets evaporated (converted into water vapour)
Latent Heat of our body is consumed in this process of evaporation
Since heat is consumed from our body, This causes our body to cool and our body temperature is maintained
Try these Questions
Why we should wear cotton clothes in summer?
In summers, we perspire more (more sweat comes from our body)
Cotton clothes are good absorber of water
They absorb water from our sweat better compared to nylon clothes
Hence they leave our body cool
Why do we see water droplets on outer of glass containing ice cold water
Water vapour present in the air gets in contact with ice-cold water
It loses energy and gets converted from gaseous state to liquid state
Thus, we see them as water droplets
