NCERT Class 7 Geography Chapter 4 - Air

Chapter 4 - Air

Question 1: How does nature balance our life? What is the result if this balance is disturbed.
Answer:
Human being release carbon dioxide in the environment which is taken up by the plants and releases oxygen which is taken by the human this makes of the balance in the nature. This balance gets disturb because of human beings as they cut the tree for their earnings of property in this way the balance of carbon dioxide and oxygen get disturbed.

Question 2: Write a short note on distribution of air pressure in atmosphere.
Answer:
Air pressure in defined as the pressure exerted by the weight of Air on Earth's surface. As we go up the layers of atmosphere the pressure falls rapidly. The air pressure is highest at sea level and decreases with height. Horizontally, the distribution of air pressure is influenced by temperature of air at a given place. In areas where temperature is high the air gets heated and rises. This creates a low pressure area. Low pressure is associated with cloudy skies.

Question 3: Give an account of different layers of atmosphere.
Answer:
There are five types of layer. They are:
1. Troposphere: It extends up to 13 km. Air is present here. All weather phenomena like rainfall, fog and hailstorm exists.
2. Stratosphere: It extends up to 50 km. It contains a layer of ozone layer. This layer is free from clouds.
3. Mesosphere: It extends up to 80 km. Meteorites burn in this layer. It is the third layer of the Earth.
4. Thermosphere: It extends up to 80 - 400 km. Ionosphere is also part of this layer. This layer helps in radio transmission.
5. Exosphere: It is the last layer. This layer is very thin. Helium and hydrogen gas float in space.

Question 4: What is wind? Mention its type.
Answer:
The movement of air from high pressure area to low pressure area is called wind. There are three types of wind. They are:
• Permanent wind: These winds constantly blow throughout the year in a particular direction. Example: the trade wind, westerlies and easterlies.
• Seasonal wind: These winds change their direction in different seasons. Example: Monsoon in India.
• Local wind: These winds blow only during a particular period of time. Example: Land and Sea breeze.

Question 5: Give an account of the composition of atmosphere.
Answer:
The composition of atmosphere contains Nitrogen (78%), Oxygen (21%). Some of the gases are present in small quantities they are Carbon dioxide (0.03%), Argon (0.93%) and other - Helium, Hydrogen, Ozone. Dust particles and water vapour are also found.

Question 6: What is the significance of greenhouse gas?
Answer:
The carbon dioxide is also called greenhouse gas as it traps the heat radiated from the Sun.

Question 7: Name the 3 type of rainfall.
Answer:
There are three types of rainfall. They are:
• Cyclonic rainfall
• Relief rainfall
• Convection rainfall

Question 8: What is insolation?
Answer:
Insolation is the incoming solar energy intercepted by the Earth. The amount of insolation decreases from the equator towards the pole.

Question 9: Give reasons
a) Wet clothes take longer time to dry on a humid day.
b) The amount of insolation decreases from equator towards poles?
Answer:

a) Wet clothes take longer time to dry on a humid day because the air has a lot of water vapour and so it can accommodate the water vapour created by the wet cloth. So, the water remains in the cloth for a long time.
b) Insolation is the incoming solar energy intercepted by the Earth. The amount of insolation decreases from the equator towards the pole. It happens as the sun rays fall slanting on the poles while they fall straight on the equator.

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