NCERT Solutions for Class 7 Social Science Geography Chapter 4 Air

Nitrogen and oxygen are two gases which make up the bulk of the atmosphere. Carbon dioxide, helium, ozone, argon and hydrogen are found in lesser quantities. Apart from these gases, tiny dust particles are also present in the air.

Nitrogen is the most plentiful gas in the air. When we inhale, we take some amount of nitrogen into our lungs and exhale it. But plants need nitrogen for their survival. They can’t take nitrogen directly from the air. Bacteria, that live in the soil and roots of some plants, take nitrogen from the air and change its form so that plants can use it.

Our atmosphere is divided into five layers starting from the earth’s surface. These are Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere.

Troposphere: This layer is the most important layer of the atmosphere. Its average height is 13 km. The air we breathe exists here. Almost all the weather phenomena like rainfall, fog and hailstorm occur in this layer.

Stratosphere: Above the troposphere lies the stratosphere. It extends up to a height of 50 km. This
layer is almost free from clouds and associated weather phenomenon, making conditions most ideal for flying aeroplanes. One important feature of stratosphere is that it contains a layer of ozone gas. We have just learnt how it protects us from the harmful effect of the sun rays.

Mesosphere: This is the third layer of the atmosphere. It lies above the stratosphere. It extends up to the height of 80 km. Meteorites burn up in this layer on entering from the space.

Thermosphere: In thermosphere temperature rises very rapidly with increasing height. Ionosphere is a part of this layer. It extends between 80-400 km. This layer helps in radio transmission. In fact, radio waves transmitted from the earth are reflected back to the earth by this layer.

Exosphere: The upper most layer of the atmosphere is known as exosphere. This layer has very thin air. Light gases like helium and hydrogen float into the space from here.

The plates move because of the movement of the molten magma inside the earth.

A huge blanket of air by which our earth is surrounded is called atmosphere. The atmosphere have following layers: Troposphere. Stratosphere Mesosphere Thermosphere Exosphere Out of these atmospheric layers, Troposphere is the most important layer of the atmosphere, which directly support life on this planet.

Nitrogen and oxygen make the bulk of the atmosphere.

Carbon dioxide creates the greenhouse effect in the atmosphere.

Whether is hour-to-hour, day to day conditions of the atmosphere. It is short-term state of the atmosphere. It is hot or cold, wet or dry.

Three types of rainfall are: Convectional rainfall Orographic rainfall Cyclonic rainfall

Air pressure is defined as the pressure exerted by the weight of air on the earth’s surface.

This happens because on a humid day, there is more water in air than a sunny day. So, air can soak less water from wet clothes i.e., rate of evaporation decreases.

Because sun rays fall vertical on the equator while slanting on the poles.

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