NCERT Solutions for Class 11 Geography Chapter 8 Composition and Structure of Atmosphere

Detailed, Step-by-Step NCERT Solutions for Class 11 Geography Chapter 8 Composition and Structure of Atmosphere Questions and Answers were solved by Expert Teachers as per NCERT (CBSE) Book guidelines covering each topic in chapter to ensure complete preparation.

Composition and Structure of Atmosphere NCERT Solutions for Class 11 Geography Chapter 8

Composition and Structure of Atmosphere Questions and Answers Class 11 Geography Chapter 8

Question 1.
Multiple choice questions :
(i) Which one of the following gases constitutes the major portion of the atmosphere?
(a) Oxygen
(b) Nitrogen
(c) Argon
(d) Carbon dioxide
Answer:
(b) Nitrogen.

NCERT Solutions for Class 11 Geography Chapter 8 Composition and Structure of Atmosphere

(ii) Atmospheric layer important for human beings is …………
(a) Stratosphere
(b) Mesosphere
(c) Troposphere
(d) Ionosphere
Answer:
(c) Troposphere.

(iii) Sea salt, pollen, ash, smoke, soot, fine soil – these are associated with
(a) Gases
(b) Dust particles
(c) Water vapour
(d) Meteors
Answer:
(b) Dust particles.

(iv) Oxygen gas is in negligible quantity at the height of atmosphere
(a) 90 km
(b) 120 km
(c) 100 km
(d) 150 km
Answer:
(b) 120 km.

NCERT Solutions for Class 11 Geography Chapter 8 Composition and Structure of Atmosphere

(v) Which one of the following gases Ls transparent to incoming solar radiation and opaque to outgoing terrestrial radiation?
(a) Oxygen
(b) Nitrogen
(c) Helium
(d) Carbon dioxide
Answer:
(d) Carbon dioxide.

Question 2.
Answer the following questions in about 30 words each :

(i) What do you understand by atmosphere?
Answer:
Atmosphere is a mixture of different gases, which envelopes the earth all round. It contains life-giving gases like oxygen for man and animals and carbon-dioxide for plants.

(ii) What are the elements of weather and climate?
Answer:
Wind, temperature, pressure, clouds, humidity and precipitation are the chief elements of weather and climate.

(iii) Describe the composition of atmosphere.
Answer:
Atmosphere is a mixture of various gases. Pure dry air consists of nitrogen, oxygen, argon and carbon dioxide.

Composition of the atmosphere

Component % by volume
Nitrogen (N2) 78.08
Oxygen (O2) 20.94
Argon (Ar) 0.93
Carbon dioxide (CO,) 0.03
Neon (Ne) 0.0018
Helium (He) 0.00005
Ozone (O) 0.00006
Hydrogen (H) 0.00005
Methane (CH4) Trace
Krypton (Kr) Trace
Xenone (Xe) Trace

Dust particles, smoke, salt, water vapour are also present in the lower layer of the atmosphere.

NCERT Solutions for Class 11 Geography Chapter 8 Composition and Structure of Atmosphere

(iv) Why is troposphere the most important layer of all the layers of the atmosphere?
Answer:
Because this layer contains dust particles and water vapour. Its thickness is greatest at the equator (about 18 km) because heat is transported to great heights by strong place in this layer. This is the most important layer for all biological activity. This helps to maintain the temperature of the earth.

Question 3.
Answer the following questions in about 150 words each :
(i) Describe the composition of the atmosphere.
Answer:
The composition of the atmosphere is shown in Table 8.2. It is clear from the table 8.2 that nitrogen and oxygen make up 99% of the clean dry air of the atmosphere. In addition, it contains small amount of C02, water vapour, ozone, inert gases like xenon, krypton, neon and argon and amounts of solid and liquid particles, collectively called aerosols.

Even though nitrogen and oxygen comprise 99% of the total volume of the atmosphere, they are climatically of little consequence. Nitrogen does not easily enter into chemical union with other substances, but gets fixed in the soil. It serves mainly as diluent or dissolves. It regulates combustion. Oxygen, on the other hand, combines with all the elements and is most combustible.

Carbon dioxide although constitutes a small percentage, it is an important gas in the atmospheric process. It can absorb heat and thus allows the lower atmosphere to be warmed up by heat radiation coming from the sun and from earth’s surface. Green plants in the process of photosynthesis utilise carbon dioxide from the atmosphere.

NCERT Solutions for Class 11 Geography Chapter 8 Composition and Structure of Atmosphere

(ii) Draw a suitable diagram for the structure of the atmosphere and label and describe it.
Answer:
The atmosphere is divided into two broad layers – homosphere and heterosphere and ten sub-layers (Table 8.1). Homosphere consists of 6 sub-layers and there are four in heterosphere.

The homosphere extends up to the height of 90 km. It is characterised by uniformity in chemical composition. It consists of three thermal layers – troposphere, stratosphere and mesosphere.

The lowest layer of homosphere is called troposphere. It is 10 km. thick at the poles and 16 km. at the equator.

Troposphere is overlain by tropopause. It separates it from the overlying layer of stratosphere. In the troposphere temperature ceases to decrease with increasing height.

The layer above the tropopause, stratosphere is the zone of clean and clear air. Jet aircrafts fly through the lower stratosphere because it provides easiest flying conditions. Stratosphere contains the ozone layer,

which absorbs the sun’s harmful ultraviolet rays. The upper boundary of the stratosphere is called stratopause. It lies at a varying altitude of about 50 km. Above the stratopause lies mesosphere. The mesosphere extend from 50-90 km. in altitude.

The second major layer, heterosphere, has heterogeneous chemical composition with layered structure of nitrogen, oxygen, helium and hydrogen. Its first layer, thermosphere, extends above mesopause, and continues to edge of space about 60,000 km. less above the earth’s surface.

NCERT Solutions for Class 11 Geography Chapter 8 Composition and Structure of Atmosphere

Temperature rises spectacularly in this layer and reaches 900°C at 350 km. Thermosphere absorbs ultraviolet radiation. This region is the source of ionosphere. Disturbances in this region appear as glowing lights of varying colours – aurora. This layer reflects radio waves. Ionized particles intermittently create a sheet like display of light called Aurora Borealis in the northern hemisphere and Aurora Australis in the southern hemisphere.

Exosphere and magnetosphere are other layers of heterosphere. Exosphere is extremely rarefied and is composed mainly of hydrogen and helium.

Magnetosphere is the outermost layer of the atmosphere. It has distinct layers of nitrogen, oxygen, helium and hydrogen.

 

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