NIOS CLASS 12 GEOGRAPHY (316) IMPORTANT NOTES FOR EXAM
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Q.
Explain the composition of Atmosphere.
(A) Gases of the atmosphere:
The atmosphere is the mixture of different types of gases, including water vapour and dust particles. Nitrogen and Oxygen are the two main gases of the atmosphere. 99 percent part of it is made up of these two gases. Other gases like organ, carbon dioxide, hydrogen, nion, helium etc. form the remaining part of atmosphere.
Ozone Gas: The amount of ozone gas in the atmosphere is very little. It is limited to the ozone layer but it is very important. It protects the living beings by absorbing the ultraviolet rays of the sun. If there was no ozone gas in the atmosphere, there would not have been existence of living beings and plants on the earth surface.
(B) Water vapour: Gaseous form of water present in the atmosphere is called water vapour. Water vapour present in the atmosphere has made life possible on the earth Water vapour is the source of all kinds of precipitation. Its maximum amount in the atmosphere could be upto 4 percent. Maximum amount of water vapour is found in hot-wet regions and its least amount is found in the dry regions. Generally, the amount of water vapour goes on decreasing from low latitudes to high latitudes.
(C) Dust Particles: Dust particles are generally
found in the lower layers of the atmosphere. These particles are found in the
form of sand, smoke and oceanic salt. Sand particle have important place in the
atmosphere. These dust particles help in the condensation of water vapour
Q.
Mention the importance of the Atmosphere.
(i) Oxygen is very important for the living beings.
(ii) Carbon dioxide is very useful for the plants.
(iii) Dust particles present in the atmosphere create suitable conditions for the precipitation.
(iv) The amount of water vapour in the atmosphere goes on changing and directly affects the plants and living beings.
(v) Ozone protects all kinds of life on the earth from the harmful ultra violet rays of the sun
Q. Describe the Structure of the Atmosphere.
The atmosphere can be divided into five layers according to the diversity of temperature and density.
1. Troposphere:
a. This is the lowest layer of the atmosphere.
b. The height of this layer is about 18 kms on the equator and 8 kms on the poles. The main reason of higher height at the equator is due to presence of hot convection currents that push the gases upward.
c. This is the most important layer of the atmosphere because all kinds of weather changes take place only in this layer. Due to these changes development of living world take place on the earth. The air never remains static in this layer. Therefore this layer is called changing sphere or troposphere.
d. The environmental temperature decreases with increasing height of atmosphere. It decreases at the rate of 10C at the height of 165 metre. This is called Normal lapse rate.
e. The upper limit of the troposphere is called tropopause. This is a transitional zone. In this zone characteristics of both the troposphere and ionosphere are found.
2.
Stratosphere:
a.
This layer is above the troposphere.
b.
This layer is spread upto the height of 50
kms from the Earth’s surface. Its average extent 40 kms.
c.
The temperature remains almost the same in
the lower part of this layer upto the height of 20 kms. After this the
temperature increases slowly with the increase in the height. The temperature
increases due to the presence of ozone gas in the upper part of this layer.
d.
Weather related incidents do not take place
in this layer. The air blows horizontally here. Therefore this layer is
considered ideal for flying of aircrafts
3.
Mesosphere:
a.
It is the third layer of the atmosphere
spreading over stratosphere.
b.
It spreads upto the height of 80 kms. from
the surface of the earth. It’s extent is 30 kms.
c.
Temperature goes on decreasing and drops
upto – 1000C.
d.
‘Meteors’ or falling stars occur in this
layer.
4.
Ionosphere:
a.
This is the fourth layer of the atmosphere.
It is located above the mesosphere.
b.
This layer spreads upto the height of 400
kms. from the surface of the earth. The width of this layer is about 300 kms.
c.
The temperature starts increasing again with
increasing height in this layer.
d.
Electrically charged currents flows in the
air in this sphere. Radio waves are reflected back on the earth from this
sphere and due to this radio broadcasting has become possible.
5.
Exosphere:
a.
This is the last layer of the atmosphere
located above ionosphere and extends to beyond 400 km above the earth.
b.
Gases are very sparse in this sphere due to
the lack of gravitational force. Therefore, the density of air is very less
here.