Air - Class 7 Geograpahy ncert

Air - Class 7 Geograpahy ncert

by Anusha Gupta

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​I HOPE YOU WILL ENJLOY THE LESSON AND THE QUESTIONS

Overview ​

Atmosphere: An atmosphere is a layer of air surrounding our planet Earth. All living beings on this earth depend on the atmosphere for their survival. It is this mass of air that has made the temperature on the earth liveable.​

Composition of the Atmosphere​

In the atmosphere, nitrogen and oxygen are found in bulk quantities. 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. Nitrogen is the most plentiful gas in the air. When we inhale, we take some amount of nitrogen into our lungs and exhale it.

Nitrogen is essential for plants to survive. They cannot take nitrogen directly from the air. Bacteria, that live in the soil and roots of some plants, take nitrogen from the air and change its form so that plants can use it.

Oxygen is the second most plentiful gas in the air. Humans and animals take oxygen from the air as they breathe. During photosynthesis, green plants produce oxygen. In this way, oxygen content in the air remains constant.

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Composition of the Atmosphere (contd.)​

Carbon dioxide is another important gas. Green plants use carbon dioxide to make their food and release oxygen. Humans or animals release carbon dioxide. The amount of carbon dioxide released by humans or animals seems to be equal to the amount used by the plants which make a perfect balance.​

​Structure of the Atmosphere

​The atmosphere is divided into five layers starting from the earth’s surface. These are Troposphere, Stratosphere, Mesosphere, Thermosphere and Exosphere.

Troposphere: This layer is the most important layer of the atmosphere. Its average height is 13 km and the air we breathe exists here. In this layer, all-weather phenomena like rainfall, fog and hailstorm occur.

Stratosphere: Above the troposphere lies the stratosphere. It extends up to a height of 50 km. This layer is free from clouds and associated weather phenomenon, which makes it most ideal for flying aeroplanes. It contains a layer of ozone gas.

Structure of the Atmosphere (contd.)​

​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 space.

Thermosphere: In thermosphere, temperature rises very rapidly with increasing height. Ionosphere is a part of this layer. It extends between 80-400 km. 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 exosphere. This layer has very thin air. Light gases like helium and hydrogen float into space from here.​

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​Weather and Climate

​Weather and Climate

Temperature: The temperature that we feel every day is the temperature of the atmosphere. The degree of hotness and coldness of the air is known as temperature. The temperature changes between day and night and season to season. Summers are hotter than winters.

Insolation: An important factor that influences the distribution of temperature is insolation. Insolation is the incoming solar energy intercepted by the earth. The amount of insolation decreases from the equator towards the poles. Therefore, the temperature decreases in the same manner.

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Weather and Climate (contd.)

Temperature​

​Temperature in cities is much higher than that of villages. The concrete and metals in buildings and the asphalt of roads get heated up during the day. This heat is released during the night. Also, the crowded high rise buildings of the cities trap the warm air and thus, raise the temperature of the cities.

​Weather and Climate ( contd.)

​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. Horizontally the distribution of air pressure is influenced by the temperature of the 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 and wet weather. In areas having lower temperature, the air is cold and heavy.

Heavy air sinks and creates a high pressure area. High pressure is associated with clear and sunny skies. The air always moves from high-pressure areas to low-pressure areas.​

​Weather and Climate (contd.)

​Wind

The movement of air from high-pressure areas to low-pressure areas is called wind. Winds can be broadly divided into three types.

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.​

Weather and Climate (contd.)

​Moisture

When water evaporates from land and different water bodies, it becomes water vapour. Moisture in the air is known as humidity. When the air is full of water vapour we call it a humid day. As the air gets warmer, its capacity to hold the water vapour increases and so it becomes more and more humid.

When the water vapour rises, it starts cooling. The water vapour condenses causing formation of droplets of water. Clouds are masses of such water droplets. When these droplets of water become too heavy to float in the air, then they come down as precipitation.

Precipitation that comes down to the earth in liquid form is called rain. On the basis of mechanism, there are three types of rainfall: the convectional rainfall, the orographic rainfall and the cyclonic rainfall.​

​Now let's proceed with some questions !!

Multiple Choice

Air is made up of atoms and molecules.

• True

• False

Multiple Choice

Air is made up of atoms and molecules.

• True

• False

Multiple Choice

What are the pollutants known to cause acid rain?

• nitrogen oxides and sulfur dioxide (sulfur compounds)

• Low pH and Acid

• Lemon Juice and Battery Acid

• Particulate Matter and Carbon Dioxide

Multiple Choice

Air has no weight.

• True

• False

Multiple Choice

What can humans do to reduce the effects of acid rain?

• Develop Alternate Energy Sources (Solar Power, Wind Energy)

• Use Less Energy

• Stop Burning Fossil Fuels

• All of the Answers are Correct

Multiple Choice

Air is made up of a mixture of many different kinds of gases.

• True

• False

Multiple Choice

Smog or ground ozone forms in the troposphere. Which pollutants are most responsible for smog or ground ozone?

• sulfur and particulate matter

• volatile organic compounds and nitrogen oxides

• carbon monoxide and carbon dioxide

• none of these answers are correct

Multiple Choice

Gases are invisible

• True

• False

Multiple Choice

CFC's cause harm to our 

• Troposphere

• Inversion Layer

• Ozone Layer

• Carbon Dioxide

Multiple Choice

Which gas is the most common in our air?

• Nitrogen

• Hydrogen

• Helium

• Oxygen

Multiple Choice

Where is the Ozone Layer found in our atmosphere?

• Troposphere (lower portion)

• Stratosphere (upper portion)

Multiple Choice

Which box below shows a more dense object?

• Left

• Right

Multiple Choice

When the Ozone Layer loses Ozone what happens to organisms on the earth's surface?

• They are exposed to Smog

• Nothing happens

• They are exposed to Acid Rain

• They are exposed to Ultraviolet B Radiation

Multiple Choice

Define Density

• The weight of a column of air pushing down on an area

• The Amount of Mass in a given volume

• The force pushing on an area

• The distance above sea level

Multiple Choice

Humans cause long and short term harm to their environment.

• true

• false

Multiple Choice

Define Pressure

• The weight of a column of air pushing down on an area

• The Amount of Mass in a given volume

• The force pushing on an area

• The distance above sea level

Multiple Choice

Burning fossil fuels cause ________ that cause pollution.

• temperature decrease

• headaches

• emissions

• natural pollution

Multiple Choice

Define Altitude

• The weight of a column of air pushing down on an area

• The Amount of Mass in a given volume

• The force pushing on an area

• The distance above sea level

Multiple Choice

These are two ways people can reduce air pollution.

• Drive vehicles that get low gas mileage / Burn trash at home

• Burn less fossil fuels / walk and ride bikes

• Create major forest fires / Use CFC's

• Burn styrofoam at landfills / Use more chlorine

Multiple Choice

Define Air Pressure

• The weight of a column of air pushing down on an area

• The Amount of Mass in a given volume

• The force pushing on an area

• The distance above sea level

Multiple Choice

Select the natural form of air pollution.

• CFC's

• Burning Fossil Fuels

• Forest Fires

• Paints and Solvents

Multiple Choice

Air pressure is measured with a

• thermometer

• hot-air balloon

• satellite

• barometer

Multiple Choice

The force pushing on an area is called density.

• True

• False

Multiple Choice

Clouds are made of water vapor (gas).

• True

• False

Multiple Choice

As I walk up Mt Everest, the density of air...

• decreases

• increases

​THANKS FOR ATTENDING THIS SESSION. I HOPE YOU LIKED IT !!