Here are important questions from Class 7 NCERT Geography Chapter 4 Air

1. What is atmosphere?

Atmosphere is the huge blanket of air that surrounds our earth.

2. Why is carbon dioxide considered a greenhouse gas?

Carbon dioxide traps the heat radiated by the earth and creates a green house effect. Hence, it is called a green house gas. If there were no carbon dioxide in the atmosphere the earth would be too cold to live in.

3. What is global warming?

When the level of carbon dioxide increases in the atmosphere due to the burning of fossil fuels or other reasons, the heat retained by it increases and hence the temperature of the earth also increases. This is called global warming.

4. What are the harmful effects of global warming?

When the temperature of earth increases, ice in the polar regions will melt. This causes sea levels to rise and there is flooding in coastal regions. Low lying coastal areas may also become submerged in water. Global warming also causes extreme changes in the climate. This can lead to the extinction of many plants and animals.

5. What is the importance of atmosphere?

The atmosphere provides us with the oxygen we breathe and protects us from the harmful effects of solar rays. If there were no atmosphere, the earth would be too hot during the day and too cold during the night and life would not be possible.

6. Which is the most abundant gas in the atmosphere?

Nitrogen

7. What percent of the atmosphere is constituted by nitrogen?

78%

8. What are the gases present in the atmosphere?

Nitrogen, oxygen, carbon dioxide, helium, ozone, argon and hydrogen are the gases present in the atmosphere. Nitrogen and oxygen constitute 99% of the atmosphere.

9. How important is nitrogen?

Nitrogen is essential for the survival of plants. Since plants cannot directly absorb nitrogen from the atmosphere, they depend on a bacterium that lives in the soil and the roots of some plants to convert atmospheric nitrogen into a form that plants can use.

10. Why is it important to preserve green plants?

Humans and animals need oxygen for their survival. Green plants produce oxygen during photosynthesis and thus oxygen content in the atmosphere remains the same. Large scale deforestation will upset this balance.

11. What causes an increase in the amount of carbon dioxide in the atmosphere?

The normal composition of carbon dioxide in the atmosphere is 0.03%. When humans and animals exhale, they release carbon dioxide into the air. Plants need carbon dioxide to make their food and to release oxygen which is breathed by animals. In normal circumstances, the amount of carbon dioxide released by humans and animals is equal to the amount of carbon dioxide absorbed by plants and this maintains the balance. However, activities such as the burning of fossil fuels upset this balance by releasing tons of carbon dioxide into the atmosphere each year. Since carbon dioxide traps the heat radiated by earth, when there is an increase in the amount of carbon dioxide, it leads to global warming which causes drastic changes in climate.

12. Name the five layers of atmosphere

The five layers are – troposphere, stratosphere, mesosphere, thermosphere and exosphere

13. Write a short note on different layers of atmosphere

Troposphere

Troposphere is the lower most layer of the atmosphere and extends up to a height of 13 km. The air we breathe exists here and weather phenomena like rain, hailstorm and snow also occur in this layer.

Stratosphere

Stratosphere is the layer above troposphere. It extends up to a height of 50 km. As this layer is free of clouds and associated weather phenomena, it is ideal for flying aeroplanes. Stratosphere has a layer of ozone gas which protects the earth from the harmful ultraviolet rays of sun.

Mesosphere

Mesosphere is the third layer of atmosphere and extends up to a height of 80 km. This is the layer of the atmosphere where meteorites burn up.

Thermosphere

This is the fourth layer of atmosphere. As we go up this layer, there is a rapid rise in temperature. Ionosphere is part of this layer and extends up to 400 km. This is the layer that helps in radio transmission by reflecting back the radio waves transmitted from the earth.

Exosphere

This is the uppermost layer of the atmosphere. There is very thin air in this layer.

14. What is weather?

Weather is the hour-to-hour, day-to-day condition of the atmosphere. It can change dramatically from day to day. For example, it can be sunny today and rainy tomorrow.

15. What is climate?

Climate is the average weather condition of a place over many years.

16. What is insolation?

Insolation is the incoming solar energy intercepted by the earth.

17. How does insolation affect the distribution of temperature?

The amount of insolation decreases from equator to the poles. This is because at the equator the sun rays fall vertically and greater amounts of them are intercepted by the earth. That is why places near the equator are hotter and those near the poles are colder.

18. What is air pressure?

Air pressure is the pressure exerted by the weight of air on the earth’s surface.

19. As we go up the different layers of the atmosphere, the air pressure, ………………………..

decreases

20. What is wind?

Wind is the movement of air from high pressure area to low pressure area.

21. What are the three types of wind?

Permanent winds, seasonal winds and local winds.

22. What are permanent winds

Permanent winds blow constantly throughout the year in a particular direction. Examples are trade winds, westerlies and easterlies.

23. What are seasonal winds?

These are winds that change their direction in different seasons. Example: monsoon winds of India

24. What are local winds?

These are the winds that blow during a particular period of the day or the year in a small area. Example: land and sea breeze

25. What is loo?

Loo is the hot and dry local wind of northern planes of India.

26. What is humidity?

Humidity is the moisture in the air at any time.

27. Why is it difficult to dry clothes on a humid day?

On a humid day there is too much water vapour in the air. Consequently, it becomes difficult to dry clothes.

28. How does it rain?

On hot days, the air gets warmer. Warm air has greater capacity to hold water vapour. When the water vapour carried by warm air rises, it begins to cool down. This condensation causes the formation of droplets of water. Clouds are large masses of such water droplets. When they become too heavy to float in the air, they come down as precipitation. When precipitation occurs in liquid form, it is rain. It can also come down as snow, hail or sleet.