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NCERT Class 7 Geography: Chapter 4 Air explores the composition and significance of Earth’s atmosphere. It explains various layers of the atmosphere, such as the troposphere, stratosphere, mesosphere, thermosphere, and exosphere, detailing their distinct characteristics. The chapter emphasizes the importance of air for sustaining life and regulating climate. It introduces concepts like air pressure, wind, and their role in weather patterns. The chapter also touches upon natural phenomena like cyclones and explains their formation.
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Important Definitions in NCERT Class 7 Geography Chapter 4
- Troposphere: This layer is the most important layer of the atmosphere. Its average height is 13 km. The air we breathe exists here. Almost all the weather phenomena like rainfall, fog, and hailstorms occur in this layer.la
- Stratosphere: Above the troposphere lies the stratosphere. It extends up to a height of 50 km. This layer is almost free from clouds and associated weather phenomena, making conditions ideal for flying airplanes.
- Mesosphere: This is the third layer of the atmosphere. It lies above the stratosphere. It extends up to a height of 80 km. Meteorites burn up in this layer on entering from the space.
- Thermosphere: In the thermosphere, temperature rises very rapidly with increasing height. The ionosphere is a part of this layer. This layer helps in radio transmission. In fact, radio waves transmitted from the earth are reflected back to the earth by this layer.
- Exosphere: The uppermost layer of the atmosphere is known as the exosphere. This layer has very thin air. Light gases like helium and hydrogen float into space from here.
- Insolation: An important factor that influences the distribution of temperature is insolation. Insolation is the incoming solar energy intercepted by the earth.
- Air Pressure: Air pressure is defined as the pressure exerted by the weight of air on the earth’s surface. As we go up the layers of the atmosphere, the pressure falls rapidly. The air pressure is highest at sea level and decreases with height.
- Wind: The movement of air from high-pressure areas to low-pressure areas is called wind.
- Permanent winds: The trade winds, westerlies and easterlies are the permanent winds. These blow constantly throughout the year in a particular direction.
- Seasonal winds: These winds change their direction in different seasons. For example monsoons in India.
- Local winds: These blow only during a particular period of the day or year in a small area. For example, land and sea breeze.
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Also Read:
| NCERT Class 7 Geography: Chapter 1 Environment |
| NCERT Class 7 Geography: Chapter 2 Inside Our Earth (Free PDF) |
| NCERT Class 7 Geography: Chapter 3 Our Changing Earth |
Download Social Science Class 7 Geography Chapter 4 Important Questions and Answers PDF
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Important Questions in NCERT Class 7 Chapter 4: Free PDF Download
1. Answer the following questions.
(i) What is the atmosphere?
Ans: 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 smaller quantities. All living beings on Earth depend on the atmosphere for their survival.
(ii) Which two gases make the bulk of the atmosphere?
Ans: Nitrogen and oxygen are two gases which make up the bulk of the atmosphere.
(iii) Which gas creates a greenhouse effect in the atmosphere?
Ans: Carbon dioxide released in the atmosphere creates a greenhouse effect by trapping the heat radiated from the earth.
(iv) What is weather?
Ans: 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) Name three types of rainfall.
Ans: The three types of rainfall are:
- Convectional rainfall
- Orographic rainfall
- Cyclonic rainfall
(vi) What is air pressure?
Abs: Air pressure is defined as the pressure exerted by the weight of air on the earth’s surface. As we go up the layers of the atmosphere, the pressure falls rapidly. The air pressure is highest at sea level and decreases with height.
2. Tick the correct answer.
(i) Which of the following gases protects us from harmful sun rays?
(a) Carbon dioxide
(b) Nitrogen
(c) Ozone
Ans: c
(ii) The most important layer of the atmosphere is
(a) Troposphere
(b) Thermosphere
(c) Mesosphere
Ans: a
(iii) Which of the following layers of the atmosphere is free from clouds?
(a) Troposphere
(b) Stratosphere
(c) Mesosphere
Ans: b
(iv) As we go up the layers of the atmosphere, the pressure
(a) Increases
(b) Decreases
(c) Remains the same
Ans: b
(v) When precipitation comes down to the earth in the liquid form, it is called
(a) Cloud
(b) Rain
(c) Snow
Ans: b
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 |
Ans:
| (i) Trade Winds | (e) Permanent wind |
| (ii) Loo | (f) Local wind |
| (iii) Monsoon | (b) Seasonal wind |
| (iv) Wind | (c) The horizontal movement of air |
4. Give reasons.
(i) Wet clothes take a longer time to dry on a humid day?
Ans: 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) Amount of insolation decreases from the equator towards poles?
Ans: Insolation is the incoming solar energy intercepted by the earth. The amount of insolation decreases from the equator toward the poles because sun rays fall vertically on the equator and slant on the poles.
Explore Notes of All subjects of CBSE Class 7:-
| CBSE NCERT Notes Class 7 English | CBSE NCERT Notes Class 7 History | CBSE NCERT Notes Class 7 Geography |
| CBSE NCERT Notes Class 7 Civics | CBSE NCERT Notes Class 7 Mathematics | CBSE NCERT Notes Class 7 Science |
Check out Class 6 Geography Notes:
FAQs
Ans: Nitrogen and oxygen are two gases that make up the bulk of the atmosphere.
Ans: Carbon dioxide released in the atmosphere creates a greenhouse effect by trapping the heat radiated from the earth.
Ans: 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.
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