Evaporation

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