Class 7 Geography Chapter 4 Question Answers - Air

Q1. Define the term atmosphere.

Ans: The atmosphere is a vast layer of air that surrounds the Earth. It is essential for life as it:

• Provides the air we breathe.
• Protects us from harmful sun rays.
• Regulates the planet's temperature, making it suitable for living beings.

Without this protective blanket, the Earth would experience extreme temperatures, making survival impossible.

Q2. Atmosphere plays a dynamic role how?

Ans: The atmosphere acts as Earth's protective blanket, playing a vital role in sustaining life. Its functions include:

• Maintaining a comfortable temperature by trapping heat.
• Creating various weather conditions, such as rain and snow.
• Providing the air we breathe, which is essential for survival.
• Supporting plant growth by supplying carbon dioxide for photosynthesis.

Key components of the atmosphere include:

• Nitrogen (78%) - the most abundant gas.
• Oxygen (21%) - essential for respiration.
• Carbon dioxide (0.03%) - contributes to the greenhouse effect, trapping heat.

However, increased levels of carbon dioxide from pollution can lead to global warming, causing climate changes and rising sea levels, which may threaten various species.

Q3. What is air circulation?

Ans: Air circulation refers to the movement of air caused by temperature differences. Here’s how it works:

• When air is heated, it becomes lighter and rises.
• Cold air is denser and sinks, creating a high-pressure area.
• As hot air rises, cold air rushes in to fill the gap, leading to continuous air movement.

This process is essential for weather patterns:

• Low-pressure areas are often associated with cloudy skies and wet weather.
• High-pressure areas typically bring clear skies and sunshine.

Wind is the movement of air from high-pressure to low-pressure areas. It can be gentle or strong, affecting our environment in various ways:

• Gentle winds can move smoke or dust.
• Strong winds can cause damage, such as uprooting trees.

Overall, air circulation plays a crucial role in our weather and climate.

Q4. Name the different layers of the atmosphere.

Ans: The atmosphere is divided into five distinct layers:

• Troposphere: This is the lowest layer, averaging 13 km in height. It contains the air we breathe and is where most weather events, such as rainfall and fog, occur.
• Stratosphere: Above the troposphere, this layer extends up to 50 km. It is mostly free from clouds and weather, making it ideal for flying. It also contains the ozone layer, which protects us from harmful sun rays.
• Mesosphere: This third layer lies above the stratosphere and extends up to 80 km. It is where meteorites burn up upon entering the atmosphere.
• Thermosphere: In this layer, temperatures rise rapidly with height. It extends from 80 km to about 400 km and includes the ionosphere, which aids in radio transmission by reflecting radio waves back to Earth.
• Exosphere: The outermost layer, characterised by very thin air, where light gases like helium and hydrogen can escape into space.

Q5. What is the greenhouse effect?

Ans: The greenhouse effect occurs when carbon dioxide in the atmosphere traps heat radiated from the Earth. This process is essential for maintaining livable temperatures on our planet.

Key points about the greenhouse effect:

• Without the greenhouse effect, the Earth would be too cold for life.
• Increased emissions from vehicles and factories raise carbon dioxide levels.
• This leads to higher temperatures, a phenomenon known as global warming.
• Global warming causes ice to melt in colder regions, resulting in rising sea levels.
• Rising sea levels can lead to flooding in coastal areas.
• Climate change may cause drastic shifts in local climates, potentially leading to the extinction of some plants and animals.

The Earth is surrounded by a protective layer of air called the atmosphere, which is vital for all living beings. It provides the air we breathe and shields us from harmful solar radiation.

While humans and animals release carbon dioxide, plants absorb it, maintaining a natural balance. However, this balance is disrupted by the burning of fossil fuels, which adds billions of tonnes of carbon dioxide into the atmosphere each year, affecting the Earth's weather and climate.

Q6. (i) Which layer makes weather phenomena possible? 
        (ii) Which layer has the most suitable conditions for flying aeroplanes?
        (iii) Which layer makes radio communication possible? 
        (iv) Which layer protects us from meteors and obsolete satellites from outer space?

Ans:

(i) Troposphere: This layer is crucial for weather phenomena, including rainfall, fog, and hailstorms. It has an average height of 13 km.

(ii) Stratosphere: Ideal for flying aeroplanes, this layer extends up to 50 km and is mostly free from clouds. It also contains ozone gas, which protects us from harmful sun rays.

(iii) Ionosphere: Part of the thermosphere, this layer facilitates radio communication by reflecting radio waves back to Earth.

(iv) Thermosphere: This layer protects us from meteors and obsolete satellites. It extends from 80 km up to 400 km, where meteors burn up upon entry.

Q7. Name the instrument which measures temperature.

Ans: Temperature is measured using a thermometer. For outdoor conditions, a mercury thermometer is commonly used.

Q8. Define low and high pressure.

Ans: Low pressure occurs when air is heated and rises, creating an area with less air pressing down. This is often linked to cloudy skies and wet weather.

High pressure happens in cooler areas where cold, heavy air sinks. This results in more air pressing down and is usually associated with clear and sunny skies.

Air moves from high pressure to low pressure areas, creating winds. Winds can vary in strength:

• Gentle winds can move leaves and dust.
• Strong winds can uproot trees and make it hard to walk.

Air pressure is the weight of air pressing down on the Earth's surface. It is highest at sea level and decreases with altitude. The distribution of air pressure is influenced by temperature:

• High temperatures lead to low pressure as air rises.
• Low temperatures result in high pressure as air sinks.

Understanding these concepts helps explain weather patterns and phenomena.

Q9. Which layer is free from water vapour and dust particles?

Ans: The stratosphere is the layer of the atmosphere that is free from water vapour and dust particles.

Q10. Define wind.

Ans: Wind is the movement of air from areas of high pressure to areas of low pressure. It can be observed in various ways:

• It can blow dry leaves along the pavement.
• During storms, it can uproot trees.
• Gentle winds can disperse smoke or fine dust.
• Strong winds can make it difficult to walk or hold an umbrella.

Winds can be classified into three main types:

• Permanent winds: These include trade winds, westerlies, and easterlies, which blow consistently throughout the year.
• Seasonal winds: These change direction with the seasons, such as the monsoons in India.
• Local winds: These occur in specific areas and times, like land and sea breezes. An example is the hot, dry wind known as loo in northern India.

Q11. What is rain? What is the importance of rainfall?

Ans:

Rain is liquid precipitation that falls to the earth's surface. It is essential for the survival of both plants and animals.

• Rain provides fresh water to the environment.
• It supports the growth of plants, which in turn sustain animal life.
• Insufficient rainfall can lead to drought and water scarcity.
• Excessive rainfall can result in floods and other natural disasters.

There are three main types of rainfall:

• Convectional rainfall
• Orographic rainfall
• Cyclonic rainfall

Overall, rainfall is crucial for maintaining the balance of our ecosystems.

Long Answer Type Questions

Q1. Describe the composition of the atmosphere.

Ans: The atmosphere is a mixture of gases with a relatively uniform composition in its lower layer. An average sample of pure dry air consists of:

• Nitrogen: 78%
• Oxygen: 21%
• Argon: 0.9%
• Other gases (like carbon dioxide, hydrogen, helium, and ozone) are present in very small amounts.

Additionally, the lower atmosphere contains water vapour in varying quantities.

Key points about the gases in the atmosphere:

• Nitrogen is the most abundant gas. While we inhale nitrogen, it is essential for plants, which cannot use it directly from the air.
• Oxygen is the second most abundant gas. Humans and animals breathe it in, while plants produce it during photosynthesis.
• Carbon dioxide is crucial for plants to make food and is released by humans and animals, maintaining a balance in the atmosphere.

Composition of atmosphere

Q2. What is global warming? What is its effect?

Ans: Global warming occurs when the heat trapped by greenhouse gases raises the Earth's temperature. This phenomenon is primarily caused by:

• Burning fossil fuels such as coal and oil.
• Deforestation, which disrupts the natural balance of gases.

The effects of global warming include:

• Melting snow and ice in polar regions.
• Rising sea levels, leading to flooding in coastal areas.
• Changes in weather patterns and climate.
• Potential extinction of certain plant and animal species.

In summary, global warming poses significant risks to our environment and biodiversity.

Q3. Explain how the oxygen and carbon dioxide balance is maintained in the air.

Ans: Green plants play a crucial role in maintaining the balance of oxygen and carbon dioxide in the air:

• Photosynthesis: Plants absorb carbon dioxide and produce oxygen.
• Respiration: Humans and animals inhale oxygen and exhale carbon dioxide.
• The amount of carbon dioxide released by humans and animals is roughly equal to what plants use, creating a natural balance.

However, this balance is disrupted by:

• Burning fossil fuels: Activities like burning coal and oil release excess carbon dioxide into the atmosphere.
• This increase in carbon dioxide contributes to global warming and affects the Earth's climate.

Additionally, deforestation can disturb this balance, leading to further environmental issues.

Q19. What is the difference between weather and climate?

Ans: Weather refers to the short-term conditions of the atmosphere, including:

• Hourly and daily changes
• Factors like temperature, humidity, and wind
• Can affect mood and activities, e.g., hot weather may cause irritability, while pleasant weather can encourage outings

Climate, on the other hand, is the long-term average of weather conditions in a specific area, typically measured over 30 years or more. It helps us understand:

• The typical weather patterns of a region
• Why we rely on daily weather forecasts to prepare for immediate conditions

Temperature is a key aspect of weather, defined as:

• The degree of hotness or coldness of the air
• Varies between day and night, and across seasons
• Influenced by insolation, the solar energy received by the Earth

In summary, while weather is about immediate atmospheric conditions, climate is about long-term trends.

Q4. What is global warming? What is its effect?

Ans: Global warming occurs when the heat trapped by greenhouse gases raises the Earth's temperature. This process is affected by human activities such as:

• Burning fossil fuels like coal and oil
• Deforestation

This increase in temperature leads to:

• Melting snow in polar regions
• Rising sea levels, which can cause floods in coastal areas
• Changes in weather patterns
• Potential extinction of certain plant and animal species

The balance of gases in the atmosphere is crucial for life. While plants absorb carbon dioxide, excessive emissions from human activities disrupt this balance, contributing to global warming.

Q5. What is the relation between temperature and pressure?

Ans: The relationship between temperature and pressure is significant in understanding weather patterns:

• High temperatures cause air to heat up and rise, leading to a low-pressure area.
• Low-pressure areas are often associated with cloudy skies and wet weather.
• In contrast, low temperatures make the air cold and heavy, causing it to sink and create a high-pressure area.
• High-pressure areas typically bring clear and sunny skies.
• Air moves from high-pressure to low-pressure areas, creating wind.

Wind can be observed in various ways:

• It can blow dry leaves along the pavement.
• Strong winds can uproot trees during storms.
• Gentle winds may disperse smoke or dust.
• Strong winds can make it difficult to walk or hold an umbrella.

Air pressure is the force exerted by the weight of air on the Earth's surface. It is highest at sea level and decreases with altitude. The distribution of air pressure is influenced by:

• Temperature: Warm air rises, creating low pressure.
• Weather conditions: Changes in temperature affect atmospheric pressure.

Understanding these concepts helps explain daily weather variations and the overall climate of a region.