Maharashtra Board Class 8 Geography Chapter 3 Humidity And Clouds PDF Download

Humidity And Clouds

Can You Tell?

Look at the pictures shown in figure 3.1. Discuss the weather conditions shown in these pictures in the class and write the descriptions in the boxes below.

Geographical Explanation

Generally, we keep talking about the weather conditions. We can identify the weather conditions through the conversations above. We experience the dampness or dryness in the air throughout the year. The changes occurring in the weather conditions in desert areas, coastal areas and mountainous areas is evident from the figures.

Rajasthan lies in a region with dry and hot air. There is hardly any moisture in the air. People wear loose cotton clothes.

Kashmir valley lies in a region with cold and dry air. Moisture is minimal in the air. People cover themselves with warm clothes.

In Mumbai, the air is hot and humid. There the proportion of moisture is very high in the air. In addition, if dark clouds cover the sky, the content of moisture in the air increases.

In the above discussion, the words hot, moist, cool etc. show the condition of the air. They relate to the content of the moisture in the air. Moisture in the air is invisible. But it is the major component of air which is taken into consideration while discussing the weather of any place. For precipitation to occur in any place, presence of moisture in the air is very important.

Teacher's Note

Moisture in air makes weather feel wet or dry. In Mumbai, monsoon season has very high moisture, like an invisible water spray in the air.

Exam Trick

Remember: Moisture = water vapour in air. You cannot see it but you feel it. In summer, air is dry. In monsoon, air feels sticky because of moisture.

Points to Remember

Weather depends on moisture in the air.
Moisture is invisible water vapour.
Desert areas are dry with little moisture.
Coastal areas have high moisture in the air.
Moisture is needed for rain to fall.

Think About It

During winters, when you exhale on the glass of your mirror, what happens. If you try to do this in summer why doesn't this happen?

Evaporation

Evaporation is the process of converting water into steam or water vapour. Because of the sun's heat, the water on the earth gets converted into water vapour. The process of evaporation is dependent on the dryness, temperature and the speed of the wind.

If the air is dry and hot, the rate of evaporation increases. The process of evaporation continues even in dry and cold air. On the other hand, evaporation occurs very slowly in moist air. If the velocity and temperature of the air is high, then evaporation occurs rapidly. If the wind is blowing slowly and the air is cooler, then evaporation occurs slowly.

Can You Tell?

In which season do the clothes dry fast?

In which season do the clothes take time to dry? What could be the reason?

What happened to the water which was poured initially?

When you were pouring water on the sponge, what did you expect?

What happened when you poured more water on the sponge?

What conclusions can you draw from this?

Teacher's Note

Evaporation happens faster in hot and dry weather. In summer, wet clothes dry quickly because heat turns water into invisible steam.

Exam Trick

Remember: Hot + Dry + Wind = Fast evaporation. In summer near a fan, clothes dry quickly. In winter near a heater, clothes dry slowly.

Points to Remember

Sun's heat turns water into water vapour.
Hot air increases evaporation speed.
Dry air increases evaporation speed.
Wind speed increases evaporation speed.
Cold and moist air slows evaporation.

Humidity In The Air

The proportion of water vapour in the air is called its humidity. The dryness or dampness of the air depends on the proportion of water vapour.

Air can hold moisture in specific quantity at specific temperature only. As air cools down, its moisture holding capacity reduces. This implies that warmer air can hold more moisture than cold air.

At a certain temperature, the moisture holding capacity of air becomes equal to the proportion of moisture present in it. This condition of the air is called saturation of the air.

Try This

Carry out the following activity in a group.

Take a colander/ tray which is deeper in the centre.

Take a piece of sponge.

On the flat part of the tray, make holes with the help of nails.

Keep the sponge on the centre of the tray/ colander.

Make sure there is no water in the sponge.

Pour water on the sponge with a big spoon.

The students in the group should note how many spoons of water have been poured. Keep pouring water with the spoon till the sponge becomes wet with water. Note what happens if you keep pouring water even after that. Now answer the following questions.

Teacher's Note

This activity shows how air absorbs moisture like a sponge absorbs water. When a sponge is full, water overflows just like when air is full of moisture, rain happens.

Exam Trick

Remember: Sponge = Air, Water = Moisture. When sponge is full, water comes out. When air is full of moisture, rain comes down.

Points to Remember

Air can hold only a certain amount of moisture.
Warmer air holds more moisture than cold air.
When air is full of moisture, it is called saturated air.
Saturation means air cannot hold any more moisture.
Extra moisture falls as rain when air is saturated.

Use Your Brain Power

In which season do the clothes dry fast?

In which season do the clothes take time to dry? What could be the reason?

This is a preview of the first 3 pages. To get the complete book, click below.