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NCERT Solutions for Class 7 Geography Social Science Chapter 4 Air

The Earth's atmosphere comprises a blend of various gases, primarily composed of roughly 78 percent nitrogen and 21 percent oxygen. Divided into five layers—Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere—the atmosphere plays a vital role. Weather denotes short-term atmospheric conditions, while climate represents the long-term average weather pattern of a region. For Class 7 students, the NCERT Solutions for Geography deliver comprehensive knowledge, offering a robust foundation for exam preparation.

Air

Question 1 :

Answer the following questions.

(i) What is the atmosphere?

(ii) Which two gases make the bulk of the atmosphere?

(iii) Which gas creates a greenhouse effect in the atmosphere?

(iv) What is weather?

(v) Name three types of rainfall.

(vi) What is air pressure?

Answer :

(i) The blanket of air surrounding the earth is called the atmosphere. The atmosphere primarily comprises nitrogen and oxygen in bulk and other gases like carbon dioxide, helium, ozone, etc. in less quantities. All living beings on earth depend on the atmosphere for their survival.

(ii) The two gases that make the bulk of the atmosphere are:

  1. Oxygen (21%)

  2. Nitrogen (78%)

(iii) Carbon dioxide is the gas that creates the greenhouse effect in the atmosphere.

(iv) The hour-to-hour or the day-to-day condition of the atmosphere is called weather. Weather can change dramatically from day-to-day. It may be classified as hot, dry, cold or wet.

(v) The three types of rainfall are as follows:

  1. Convectional rainfall

  2. Orographic rainfall

  3. Cyclonic rainfall

(vi)  Air pressure is defined as the pressure exerted by the weight of air on the earth’s surface. The air pressure decreases as height increases and is the highest at the sea level.


Question 2 :

Tick the correct answer.

(i) Which of the following gases protects us from harmful sun rays?

     (a) Carbon dioxide

     (b) Nitrogen

     (c) Ozone

(ii) The most important layer of the atmosphere is

     (a) Troposphere

     (b) Thermosphere

     (c) Mesosphere

(iii) Which of the following layers of the atmosphere is free from clouds?

     (a) Troposphere

     (b) Stratosphere

     (c) Mesosphere

(iv) As we go up the layers of the atmosphere, the pressure

     (a) Increases

     (b) Decreases

     (c) Remains the same

(v) When precipitation comes down to the earth in the liquid form, it is called

     (a) Cloud

     (b) Rain

     (c) Snow

 

Answer :

(i) c

(ii) a

(iii) b

(iv) b

(v) b


Question 3 :

Match the following.

(i) Trade Winds

(a) Incoming solar energy

(ii) Loo

(b) Seasonal wind

(iii) Monsoon

(c) The horizontal movement of air

(iv) Wind

(d) A layer of ozone gas

 

(e) Permanent wind

 

(f) Local wind

 

Answer :

(i) Trade Winds

(e) Permanent wind

(ii) Loo

(f) Local wind

(iii) Monsoon

(b) Seasonal wind

(iv) Wind

(c) The horizontal movement of air

 


Question 4 :

Give reasons.

(i) Wet clothes take longer time to dry on a humid day?

(ii) Amount of insolation decreases from the equator towards poles?

Answer :

(i) Wet clothes take longer time to dry on a humid day because the amount of water in the air is more on a humid day than on a sunny day. Due to this, the rate of evaporation decreases and air soaks in less water from the clothes.

(ii) Insolation is the incoming solar energy intercepted by the earth. Amount of insolation decreases from the equator toward poles because sun rays fall vertically on the equator and slant on the poles.


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