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NCERT Class 11 Geography Chapter 8 Composition and Structure of Atmosphere
Also, you can read the NCERT book online in these sections Solutions by Expert Teachers as per Central Board of Secondary Education (CBSE) Book guidelines. CBSE Class 11 Geography Solutions are part of All Subject Solutions. Here we have given NCERT Class 11 Geography Part I: Fundamentals of Physical Geography, Part II: Indian: Physical Environment, Part III: Practical Work in Geography. NCERT Class 11 Geography Chapter 8 Composition and Structure of Atmosphere Notes, NCERT Class 11 Geography Textbook Solutions for All Chapters, You can practice these here.
Composition and Structure of Atmosphere
Chapter: 8
GEOGRAPY [ PART – I ]
SHORT ANSWER TYPE QUESTIONS
Q.1. How is the atmosphere held to the earth?
Ans. Atmosphere is a gaseous envelope extending thousands of kilometres above the surface of the earth. It is held to it by the force of gravity.
Q.2. What is the tropopause?
Ans. The tropopause is an imaginary plane lying between stratosphere and troposphere.
Q.3. What is heterosphere?
Ans. Heterosphere is a layered thermosphere extending above the mesopause and continues to the edge of space about 600 km above the earth, surface.
Q.4. Which is the lowermost layer of the atmosphere?
Ans. Troposphere.
Q.5. Which layer reflects the radio waves back to the earth?
Ans. Ionosphere.
Q.6. Which of the layers of the atmos-phere is most ideal for flying the aeroplanes?
Ans. Stratosphere.
Q.7. Which layer of the atmosphere absorbs the ultraviolet rays of the sun?
Ans. The ozone layer absorbs the ultra- violet rays of the sun.
Q.8. What is the importance of ionosphere?
Ans. Ionosphere reflects back to the earth the radio waves transmitted from the earth.
Q.9. Which gases do not take part in the chemical reactions?
Ans. Neon, Argon, Krypton, Xenon and Radon.
Q.10. What are aerosols?
Ans. The huge amount of solid and liquid particles are collectively called aerosols.
Q.11. Which gas despite its small percentage is crucial in atmospheric processes?
Ans. Ozone.
Q.12. What is the importance of ionosphere?
Ans. Ionosphere reflects back to the earth the radio waves transmitted from the earth.
Q.13. Which gas is the most essential for life?
Ans. Oxygen.
Q.14. Which constituents of atmosphere are great importance for the earth’s climatic conditions?
Ans. Carbon dioxide, dust particles, water vapour and ozone.
Q.15. Which are the major constituents of clean dry air of atmosphere?
Ans. Gases like nitrogen, oxygen, etc.
Q.16. Name two major constituents of the atmosphere apart from the gases.
Ans. Dust particles and the water vapour.
Q.17. Name the thin layer which separates troposphere and stratosphere.
Ans. Tropopause.
Q.18. What is the height of troposphere at the equator and the poles respectively.
Ans. 18 km and 8 km respectively.
Q.19. Give a single term for each of the following:
(i) The layer which separates the troposphere and stratosphere.
Ans. Tropopause.
(ii) Lowermost layer of the atmosphere.
Ans. Troposphere.
(iii) A useful gas found in small amount in the atmosphere that shields the earth from the ultra-violet rays.
Ans. Ozone.
(iv) Sheet-like displays of light in the Northern Hemisphere caused by ionised particles in the atmosphere.
Ans. Aurora borealis.
(v) Physical condition or state of atmosphere at any given time.
Ans. Weather.
(vi) The luminous phenomena seen in the night sky in high altitudes in the Southern Hemisphere.
Ans. Aurora borealis.
Q.20. What is meant by the normal lapse rate?
Ans. The temperature decreases with the height in the troposphere at the rate of 0.65°C per 100 metre or 1°C per 165 metre of ascent. This is known as the normal lapse rate.
SHORT ANSWER TYPE QUESTIONS
Q.1. What do you understand by atmosphere?
Ans. Atmosphere is a vast expanse of air which envelope the earth all around. It is a mixture of different gases.
Q.2. What are the elements of weather and climate?
Ans. The elements of weather and climate are: wind, temperature, pressure, clouds, humidity and precipitation.
Q.3. What is the significance of small solid particles in the atmosphere?
Ans. The small solid particles present in the atmosphere originate from different sources and include sea salts, fine soil, smoke-soot, ash, pollen, dust and disintegrated particles of meteors. Most of the solid particles are kept in suspension in the atmosphere. These particulates help in the scattering of solar radiation which adds varying charming colour of red and orange at dawn and dusk. The selective scattering of solar radiation by dust particles make the sky appear blue. Dust and salt particles act as hygroscopic nuclei around which water vapour condenses to produce clouds. Thus there is a great significance of small solid dust particles (the particulate matter) in the atmosphere.
Q.4. Distinguish between the troposphere and stratosphere.
Ans.
| Troposphere | Stratosphere |
| 1. It is the lowermost layer of the atmosphere. | 1. It is the second layer of the atmosphere above the earth. |
| 2. Its height varies from 8 km at the poles to 18 km at the equator. | 2. Its height goes upto 50 km. |
| 3. In this layer the temperature decreases at the rate of 1°C per 165 metres. | 3. In this layer temperature is very low and mainly constant. |
| 4. It is a zone of convection currents. | 4. It is the non-convective zone of the atmosphere. |
| 5. Most of the water vapours, clouds and dust particles are found in this layer. | 5. Clouds, dust particles and water vapours are practically absent in this layer. |
| 6. Atmospheric disturbances are confined to this zone. | 6. This zone is free from atmospheric disturbances. |
Q.5. Describe the composition of atmosphere.
Ans. Atmosphere is a mixture of many discrete gases, water vapours, and dust particles.
1. Gases: Nitrogen (78%), Oxygen (21%) are the two major gases. The remaining 1% is composed of a number of gases like hydrogen argon, ozone, helium, carbon dioxide, etc. oxygen is the most vital gas for sustaining life.
The various gases present in the atmosphere are as:
| Constituent | Formula | Percentage by Volume |
| Nitrogen | N₂ | 78.08 |
| Oxygen | O₂ | 20.95 |
| Argon | Ar | 0.93 |
| Carbon dioxide | CO₂ | 0.036 |
| Neon | Ne | 0.002 |
| Helium | He | 0.0005 |
| Krypton | Kr | 0.001 |
| Xenon | Xe | 0.00009 |
| Hydrogen | H₂ | 0.00005 |
2. Water Vapour: The amount of water vapour varies from place to place and time to time. It represents 2% of the air by volume. It is mostly found in the lower layers.
3. Dust Particles: These are also found in the atmosphere in different sizes. The major sources of dust particle are deserts, lakes and dry rivers etc. These are found in the lower layers of the atmosphere. These are responsible for the formation of clouds, fog and smog.
Q.6. Why is troposphere the most important of all the layers of the atmosphere?
Ans. The troposphere is the most important of all the layers of the atmosphere because:
1. All the weather-making processes take place this layer.
2. Great contrast in climate and weather patterns are observed at different altitudes due to changes of temperature in this layer.
3. The presence of the large amount of water vapour in this layer is responsible for condensation, clouds and precipitation.
4. Dust particles give rise to fog, clouds smog, etc. in this layer.
5. Convection currents are formed to this layer for the heating and cooling of the air.
6. The air is unstable in this layer and gives rise to atmospheric disturbances like stormy cyclones.
Q.7. Explain important features of ionosphere.
Ans. The ionosphere is located between 80 and 400 km above the mesopause. It contains electrically charged particles known as ionosphere. Radio waves transmitted from the earth are reflected back to the earth by this layer. Temperature here starts increasing with height.
Q.8. Explain about dust particles
Ans. Dust particles:
(i) Dust particles are concentrated in the lower layers of the atmosphere but some time conventional currents take them to the higher height.
(ii) Dust particles includes sea salts, fine soil smoke ashes pollens dust disintegrated particles of metiors.
(iii) Dust particles produce optical phenomenon which makes the sky look beautiful at dawn and dusk.
(iv) Sky looks blue due to the presence of dust particles and water vapour which are scattered in the atmosphere.
(v) Dust particles and salt particles act as a hygroscapic into water vapour to produce clouds.
Q.9. Explain the importance of Ozone gas.
Ans. Ozone sphere extends between 10-15 km above the surface of earth. It acts as a filter and absorbs the ultra violet rays radiating from the sun. These rays do not reach the earth. It shield the life on the earth from intense harmful form of energy.
Q.10. What are the main characteristics of atmosphere ?
Ans. 1. The atmosphere is a vast envelope of gases.
2. The heavier gases are found in lower layers.
3. The atmospheric pressure decreases with altitude.
4. Atmosphere is mobile, elastic and both compressible and expansible.
Q.11. What is the importance of atmosphere to man?
Ans. The atmosphere is important to the man in the following ways:
1. Atmosphere makes the earth habitable.
2. Life supporting gases are found in the atmosphere. These are oxygen and nitrogen for animal and plant life.
3. It is the store house of water vapour.
4. It protects us from the falling meteors.
5. It absorbs ultraviolet rays.
Q.12. What are the properties of the troposphere?
Ans. 1. It is the lowest layer of the atmosphere.
2. Its average height is about 16 km.
3. In this layer the temperature decreases at the rate of 1°C per 165 m.
4. It is a zone of convection currents.
Q.13. Write short notes on:
(i) Origin of the atmosphere.
Ans. Today’s atmosphere is the result of very gradual changes starting about 5 billion years ago, by accretion of cold particles, chiefly of iron and magnesium, silicate iron and graphite. Then the earth was too small to retain the primordial atmosphere of light gases. Gravitational collapse and radioactive decay caused earth to heat up and the materials differentiated giving central solid nickle-iron core, liquid iron silicate shell mantle and lithosphere. In this way degassing took place forming a new atmosphere and hydrosphere.
(ii) The lowermost layer of Homosphere.
Ans. The lowermost layer of the homosphere is called troposphere. It is 16 km thick at the equator and 9-10 km thick at the poles. The temperatures decreases with altitude because the atmosphere is heated more by the heat radiated from the earth’s surface. In this layer the temperature because upward at the rate of 0.65°C per 100 metre. Most of the atmospheric processes take place in this layer.
Q.14. What is the significance of dust particles in the atmosphere?
Ans. Atmosphere contains many impurities in the form of dust particles. The sources of these dust particles include hot desert lake beds beaches dry river beds, volcanic eruptions and metears. Dust particles are important due to the following reasons:
(i) These play an important part in heating and cooling of the atmosphere.
(ii) These affect insolation by the processes of scattering and absorbing sun rays.
(iii) The dust particles serve as hygroscopic nuclie for the condensation of water vapour.
(iv) These are responsible for formation of clouds sunset haze fog and smog.
(v) It effects the visibility of the atmosphere.
Q.15. Give the difference between weather and climate.
Ans.
| Weather | Climate |
| 1. Weather stands for actual atmospheric conditions for a short period. | 1.Climate is the aggregate of atmosphere conditions for a longer period (say 35 years). |
| 2. The weather changes from day to day thus cannot be generalised. | 2. The climate is everlasting and static. It does not change so frequently. |
| 3. Weather depends up on the dominent element at the particular time say rainfall temperature etc. | 3. Climate is the composit picture of all the elements spread over a longer period. |
| 4. Weather is actually present at a place. It is what you get. | 4. Climate is what you expect. It is arrived at by means or average. |
Q.16. What is an important feature of troposphere?
Ans. The troposphere is the lowermost layer of the atmosphere. Its average height is 13 km and extends roughly to a height of 8 km near the poles and about 18 km at the equator. Thickness of the troposphere is greatest at the equator because heat is transported to great heights by strong convectional currents. This layer contains dust particles and water vapour. All changes in climate and weather take place in this layer. The temperature in this layer decreases at the rate of 1 C for every 165 m of height.
Q.17. Write a short note on water vapours.
Ans. • The amount of water vapour decreases with the altitudes. In warm and wet tropics, it accounts for 4% of the air by volume whereas in dry and cold areas of deserts and polar regions, it may be less then 1% of the air.
• It also decreases from the equator towards the poles.
• It absorbs parts of the insolation received from the sun and preserves the earth’s radiated heat and thus acts as a blanket by allowing the earth neither to become too hot nor too cold.
Q.18. Explain about dust particles.
Ans. • Dust particles are concentrated in the lower layers of the atmosphere but sometimes conventional currents take them to the higher height.
• Dust particles includes sea salts, fine soil, smoke, ashes, pollens, dust, disintegrated particles of meteors.
• Dust particles and salt particles act as a hygroscopic nuclei around which water condenses into water vapour to produce clouds.
• Dust particles produce optical phenomenon which makes the sky look beautiful at dawn and dusk.
• Sky looks blue due to the presence of dust particles and water vapour which are scattered in the atmosphere.
LONG ANSWER TYPE QUESTIONS
Q.1. Describe the composition of the atmosphere.
Or
What is the importance of oxygen,nitrogen and carbon dioxide in the atmosphere.
Ans. Many gases are found in the atmosphere but it can be considered to be composed of mainly nitrogen and oxygen. A rough estimate of the composition of the atmosphere is given in the following Table:
| S. No. | Gases | Percentage Composition |
| 1. | Nitrogen (N₂) | 78.08 |
| 2. | Oxygen (O₂) | 20.94 |
| 3. | Argons and (Ar) other rare gases | Less than 1 |
| 4. | Carbon dioxide (CO₂) | 0.03 |
| 5. | Neon (Ne) | 0.0018 |
| 6. | Helium (He) | 0.0005 |
| 7. | Ozone (O₂) | 0.00006 |
| 8. | Hydrogen (H) | 0.00005 |
Other rare gases are hydrogen, helium and ozone. Besides water vapour, dust particles, smoke, salts and other impurities are also present in the air, in varying quantities. As a result, the composition of air is never constant. It varies from time to time and place to place. However, if these variable elements are removed from the atmosphere, its make-up would be fairly constant all over the earth, at least in the lower atmosphere.
Of the many constituents, carbon dioxide, dust particles, water vapour and ozone are of great importance for the earth’s climatic conditions.
The nitrogen does not easily enters into chemical union with other substances, but gets fixed into the soil. It serves mainly as diluent or dissolver. It regulates combustion. Oxygen on the other hand combines with all the elements and is most combustible. Carbon dioxide is an important gas in the atmospheric processes. It can absorb heat and thus allows the lower atmosphere to be warmed up by the heat radiation coming from the sun and from the earth’s surface. Green plants in the process of photosynthesis utilise carbon dioxide from the atmosphere.
Q.2. Draw a suitable diagram for the structure of the atmosphere and label it and describe it.
Ans. Description of the structure of the atmosphere:
Atmosphere consists of almost concentric layers of air. These layers are of varying temperature and density. Density is highest near the earth’s surface and goes on decreasing upwards.
Atmosphere can be divided into five layers of air. They are:
1. Troposphere.
2. Stratosphere.
3. Mesosphere.
4. Ionosphere.
5. Exosphere.
1. Troposphere: It is the lowest layer of the atmosphere. It extends roughly up to a height of 9-10 km near the poles and about 18 km at the equator. The temperature decreases with the height in this layer. The normal lapse rate of temperature is 1°C for 165 metres. It is a vast physical laboratory of the air in which nature is always showing some experiment, on a grand scale. Formation of clouds and various forms of precipitation; heating and cooling and development of pressure system; blowing of winds and the acts of respiration by all types of life, are all taking place in this layer of the atmosphere. It is an unstable layer of the atmosphere. The vertical currents moving throughout the year make it unstable. All weather changes occur in this layer which are useful for the life on earth.
Tropopause: The upper layer of troposphere is called tropopause. It is a thin layer and its height changes according to latitudes. In fact, this is a transitional zone which connects the lower troposphere with the upper stratosphere.
2. Stratosphere: It extends up to the height of 50 km. The temperature remains constant up to the height of 20 km, in this layer. Afterwards, it increases upto the height of 50 km because of the presence of ozone. The ozone absorbs the most harmful ultraviolet rays of the sun. Clouds are almost absent in this layer. There is very little of dust particles and water-vapour in this. The air movements are horizontal. It provides ideal flying condition for jet aeroplanes because, it is free from clouds and other weather disturbances.
3. Mesosphere: The mesosphere lies above the stratosphere, which extends upto a height of 80 km. In this layer, once again, temperature starts decreasing and reaches upto to -100°C at the height of 80 km.
4. Ionosphere: It is located between 80 and 400 km. It is an electrically charged layer. Radio waves transmitted from the earth are reflected back to the earth by this layer. Temperature again starts to increase with height because of sun’s radiation.
5. Exosphere: It is the uppermost layer of the atmosphere extending beyond the ionosphere. This layer is extremely (rarefied) and gradually merges with the outer space.
In fact, we know very little about the atmosphere extending beyond 64 km above the sea-level.
Q.3. Discuss the principal elements of weather and climate and the major geographical factors affecting them.
Ans. The principal elements of weather and climate are temperature, pressure, winds, humidity, clouds and precipitation. They are called elements because they are the ingradients out of which various weather and climate types are formed. The temperature and precipitation are the main basic elements to which pressure, winds and other elements are related. Temperature expresses intensity of heat. Moisture present in the atmosphere may be precipitated in the form of rain, hail, and snow.
The various geographical factors affecting weather and climate are:
1. Latitude.
2. Distribution of land and water.
3. The great semi-permanent high and low pressure belts.
4. Winds.
5. Altitude.
6. Mountain barriers.
7. Ocean currents.
8. Storms of various kinds.
These control produce changes in temperature and precipitation which in turn give rise to a variety of weather and climates.
Q.4. Describe the role of water vapour in the weather processes.
Ans. Water vapour is the result of vaporation from water bodies on the earth. Water vapour represents about 2% of the air by volume. The presence of water vapour in the atmosphere is of primary importance in weather phenomena.
(i) It reduces the amount of insolution reaching the earth’s surface by absorption.
(ii) It acts like an insulating blanket by preserving the earth radiation. It allows the earth neither to become too cold nor too hot.
(iii) Water vapour condenses into clouds and fogs.
(iv) Water vapour is the main source of energy giving rise to cyclons storms etc.
(v) Water vapour both releases and consumes latent heat of condensation which cools and warms the air.
(vi) Water vapour makes the air stable and unstable.
(vii) Water vapour is the basic cause of all condensation and precipitation.
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