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NIOS Class 12 Geography Chapter 9 Structure And Composition of Atmosphere
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Structure And Composition of Atmosphere
Chapter: 9
GEOGRAPHY
TEXTUAL QUESTION & ANSWER
INTEXT QUESTION 9.1
Q.1. Which are the two main gases of the atmosphere?
Ans. (a) Nitrogen.
(b) Oxygen.
Q.2. In which region the maximum amount of water vapour is found?
Ans. In hot wet region.
Q.3. What is the main function of ozone gas?
Ans. The main function of the ozone gas is to absorb the harmful ultra violet rays of the sun.
INTEXT QUESTIONS 9.2
Q.1. Define tropopause.
Ans. The upper limit of the troposphere is called tropopause. This is a transitional zone.
Q.2. Why is there a difference in the height of troposphere?
Ans. The difference in the height of troposphere is the presence of hot convectional currents that push the gases upward.
Q.3. In which two spheres the temperature increases with the height?
Ans. In stratosphere and in ionosphere.
Q.4. From which sphere are the radio waves reflected?
Ans. From ionosphere.
Q.5. In which layer of the atmosphere the density of the air is the least?
Ans. Exosphere.
Q.6. In which layer of the atmosphere is the ozone gas found?
Ans. Stratosphere.
INTEXT QUESTIONS 9.3
Q.1. What is the main source of carbon?
Ans. The main source of carbon is fossil fuels like coal, petroleum and natural gas.
Q.2. What is the main source of oxygen?
Ans. The main source of oxygen are plants and trees.
Q.3. What is the percentage of nitrogen in the atmosphere?
Ans. It is 78%.
TERMINAL QUESTIONS
Q.1. Which is called atmosphere?
Ans. The air surrounding the earth is called atmosphere. The atmosphere is made of different type of gases including water vapour and dust particles.
Q.2. Distinguish between troposphere and stratosphere.
Ans.
| Troposphere | Stratosphere |
| 1. This is the lowest layer of the atmosphere. | 1. This layer is above troposphere. |
| 2. The height of this layer is about 18 km on equator and 8 km on poles. | 2. It is spread upto the height of 50 km. |
| 3. All the weather phenomena take place in this layer. | 3. The temperature remains almost same in the lower part of this layer. |
| 4. The temperature decrease with 1°C per 165 m of height. | 4. This layer is suitable for flying of aircrafts. |
| 5. The upper limit of this layer is called tropopause. It is a transition zone. | 5. Weather related phenomena do not take place in this layer. |
Q.3. State the importance of ozone gas.
Ans. 1. Ozone gas is very important to us.
2. It protects the living beings by absorbing the ultra violet rays of the sun.
3. If there was no ozone gas in the atmosphere there would not have been existence of living beings and plants on the earth’s surface.
Q.4. Explain the cycle process of nitrogen gas.
Ans. Nitrogen gas are important element for life. The amount of nitrogen gas in the atmosphere is 78%. The main source of nitrogen are nitrates present in the soil. From the atmosphere nitrogen enters into biocomponents through the biological and industrial process. Nitrogen compounds from the plants are transferred to the animals through food chain. The process of transformation of nitrogen gas of the atmosphere into nitrogen components is called nitrogen fixation. Bacterias decompose dried plants and dead animals. It produces nitrogen gas which goes back into the atmosphere. In this way the cycle of nitrogen gas is complete.
Q.5. Explain the oxygen cycle with the help of a diagram.
Ans. Oxygen Cycle: The amount of oxygen is about 21% in the atmosphere and all living beings use oxygen present in the atmosphere. It is essential to burning fuel like coal, wood and gas etc. The main source of oxygen in the atmosphere are plants and tree. Higher the number of trees and plants the availability of oxygen will be more. Oxygen also produced through photosynthesis by the green plants goes back to the atmosphere. In this way the process of oxygen cycle goes on continuously.
Q.6. Describe the structure of the atmosphere with the help of a diagram.
Ans. The atmosphere is an integral part of the earth. It surrounds the earth from all sides. It can be divided into five layers according to the diversity of temperature and density these are:
1. Troposphere.
2. Stratosphere.
3. Mesosphere.
4. Ionosphere.
5. Exosphere.
Troposphere: It is the lowest layer of the atmosphere. It’s thickness is 8 km on the poles ana 18 km on the equator. The temperature decrease in troposphere with the increase in hight at an average rate of 1°C per 165 metres. All forms of life exist in this layer. All the weather phenomena take place in this layer.
Stratosphere: It is beyond the troposphere. Ozone is present in the upper portion of the troposphere. This layer presents the ideal condition for the air flights. Ozone present in this layer prevent the ultra violet rays of the sun.
Mesosphere: Mesosphere is the third layer of the atmosphere. It is above the stratosphere. It extends upto an average height of 80 km from the mean sea level. Temperature decrease again and reaches upto 100°C at the hight of 80 km. Meteors or falling stars occur in this layer.
Ionosphere: This is the forth layer of the atmosphere. It is like located above the mesosphere. It contains electrically charged ions that reflect the radio waves back to the earth, thus wireless communication and radio broadcasting process has become possible.
Exosphere: This is the uppermost layer of the atmosphere. The exact height of this layer is uncertain. It is transition zone between the atmosphere and space. The density of this layer is very low.
