CLASS-7
GEOGRAPHY
CHAPTER-4
AIR
1. Name the different layers of the atmosphere.
Ans.- Our atmosphere is divided into five layers starting from the earth’s surface. These are –
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere and
- Exosphere
2. Explain the composition of atmosphere.
Ans.- Composition of atmosphere-
- Nitrogen and oxygen are two gases which make up the bulk of the atmosphere.
- Carbon dioxide, helium, ozone, argon and hydrogen are found in lesser quantities.
- Apart from these gases, tiny dust particles are also present in the air.
3. Define humidity.Why do wet clothes take longer to dry and sweat from our body not evaporate easily on a humid day?
Ans.- Moisture in the air at any time is known as humidity.
On a humid day the air already has sufficient amount of water vapor present. As a result the rate of evaporation decreases and hence it takes long to dry wet clothes in humid weather.
4. What is global warming? How does it affect us?
Ans.- When the level of carbon dioxide increases in the atmosphere due to factory smoke or car fumes, the heat retained increases the temperature of the earth. This is called global warming.
Effects of global warming-
- This rise in temperature causes the snow in coldest parts of the world to melt.
- As a result the sea level rises, causing floods in the coastal areas.
- There may be drastic changes in the climate of a place leading to extinction of some plants and animals in the long run.
5. Define air pressure. How are low pressure and high-pressure areas created?
Ans.-
- Air pressure is defined as the pressure exerted by the weight of air on the earth’s surface.
- In areas where temperature is high the air gets heated and rises. This creates a low pressure area.
- In areas having lower temperature, the air is cold. It is therefore heavy. Heavy air sinks and creates a high pressure area.
6. Mention any three importance of rainfall.
Ans.-
- Rainfall is very important for the survival of plants and animals.
- It brings fresh water to the earth’s surface.
- If rainfall is less – water scarcity and drought occur. On the other hand if it is more, floods take place.
7. What is wind? Explain the 3 types of winds.
Ans.- Wind– Moving air is known as wind.
Three types of wind are-
- Permanent winds
- Seasonal winds
- Local winds
- 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.
8. Give the characteristics of Thermosphere.
Ans.- The three characteristics of Thermosphere are as follows-
- In this layer, temperature rises rapidly with height.
- Ionosphere is a part of this layer.
- It helps in radio transmission.
9. What are the main characteristics of Stratosphere?
Ans.- The three characteristics of Stratosphere are as follows-
- This layer is almost free from clouds and associated weather phenomenon, making conditions most ideal for flying aeroplanes.
- It contains a layer of ozone gas.
- It also protects us from the harmful effect of the sun rays.
10. Name the three different types of rainfall. Discuss the main features of each one.
Ans.- On the basis of mechanism, there are three types of rainfall:
- Convectional rainfall
- Orographic rainfall
- Cyclonic rainfall
- Conventional rainfall
This type of rainfall occurs in areas of high temperature, particularly during summer months. When solar intensity increases during the afternoon, large-scale moisture is evaporated rapidly and they condense at high altitude causing intensive rainfall. Ex: In northern India during summer months. - Orographic rainfall
This form of rainfall happens at the foot and windward side of a mountain. As moisture-laden clouds approach high mountains, they ascend along the slope, and as a result, they condense and form rainfall. This rainfall usually results in some areas at the other side of the mountain become drought-prone. Ex: The Western Ghats in India. - Cyclonic rainfall
Cyclonic rainfall occurs when pressure difference creates storms and cyclones. The cyclonic system will bring large amount of rainfall as it approaches land. Ex: Coastal India.
11. A super cyclone occurred on 29thoct 1999, that devastated large portion of Odisha.
i) Which factors caused the damage?
Ans.- The damages caused were mainly due to three factors: wind velocity, rain and tidal surge.
ii) What were the impacts of the cyclone?
Impacts of the cyclone
- Houses were also blown away.
- Power supply and telecom lines snapped completely.
- Heavy rain occurred. These rains led to flooding.