Air - Class 7 Chapter Wise Question and Answer

Q1. Write a short note on atmosphere.

Ans: Our earth is surrounded by a huge blanket of air called atmosphere. All living beings on this earth depend on the atmosphere for their survival. It provides us the air we breathe and protects us from the harmful effects of the sun’s rays.

Q2. Discuss about the composition of the atmosphere.
Ans: 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 and after that oxygen is the most plentiful gas in the air. Humans and animals use these gases. Green plants produce oxygen during photosynthesis. Carbon dioxide is another important gas. Green plants use carbon dioxide to make their food and release oxygen. Humans or animals release carbon dioxide.
Q3. Discuss about the structure of the atmosphere.
Ans: Our atmosphere is divided into five layers. These are –
I) Troposphere:
This layer is the most important layer of the atmosphere. Its average height is 13 km. Almost all the weather phenomena like rainfall, fog and hailstorm occur in this layer.
II) Stratosphere:
Above the troposphere lies the stratosphere. It extends up to a height of 50 km. One important feature of stratosphere is that it contains a layer of ozone gas.
III) 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.
IV) 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.
V) 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.

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