Class 7 Geography: Air – Topic-wise Important Questions & Answers
(CBSE NCERT) | Horizon Academy
Greenhouse effect and Global Warming
1. What is the greenhouse effect?
The greenhouse effect is the process in which gases like carbon dioxide trap heat from the sun in the earth’s atmosphere. This keeps the earth warm and makes it possible for life to exist.
2. Why is carbon dioxide called a greenhouse gas?
Carbon dioxide is called a greenhouse gas because it traps the heat radiated from the earth, just like glass traps heat inside a greenhouse.
3. What would happen if there was no carbon dioxide in the atmosphere?
If there was no carbon dioxide in the atmosphere, the earth would have been too cold for living beings to survive. We need some carbon dioxide to keep the earth warm enough for life.
4. What is global warming?
Global warming is the increase in the temperature of the earth due to more greenhouse gases like carbon dioxide being added to the atmosphere, mainly from factory smoke or car fumes.
5. How does carbon dioxide increase in the atmosphere?
Carbon dioxide increases in the atmosphere due to burning of fuels in factories and vehicles, such as from factory smoke and car fumes.
6. What are the effects of global warming?
- Melting of snow and ice in the coldest regions of the world
- Sea level rises, causing floods in coastal areas
- Drastic changes in climate at different places
- Extinction of some plants and animals in the long run
7. How can sea level rise because of global warming?
When the temperature of the earth increases, the snow and ice in very cold places melt. This water goes into the sea and makes the sea level rise, which can cause floods in areas near the coast.
8. Why is the greenhouse effect both good and bad?
The greenhouse effect is good because it keeps our earth warm enough to live. But too much greenhouse effect (due to more carbon dioxide) is bad because it makes the earth too hot.
9. What can happen if climate changes drastically due to global warming?
Drastic changes in climate due to global warming can lead to some plants and animals not being able to survive. This can cause them to become extinct.
10. Name two main sources that increase carbon dioxide levels in the atmosphere.
The two main sources are:
- Smoke from factories
- Fumes from cars and other vehicles
11. How does the greenhouse effect relate to the survival of living beings on earth?
The greenhouse effect keeps the earth’s temperature suitable for living beings. Without it, the earth would be too cold to live on.
Composition of Atmosphere
1. What is the atmosphere?
The atmosphere is a huge blanket of air that surrounds the earth. It is very important for the survival of all living beings on earth.
2. How does the atmosphere help living beings?
The atmosphere provides us the air we breathe and protects us from the harmful rays of the sun. It keeps the temperature of the earth suitable for life. Without the atmosphere, days would be extremely hot and nights would be very cold, making life impossible.
3. Why is the air described as a mixture of gases?
Air is described as a mixture of gases because it is made up of many different gases like nitrogen, oxygen, carbon dioxide, helium, ozone, argon, and hydrogen. Tiny dust particles are also present in the air.
4. Which are the two main gases present in the atmosphere and what is their importance?
The two main gases in the atmosphere are nitrogen and oxygen.
- Nitrogen is the most plentiful gas. Plants need nitrogen for their growth, but they cannot use it directly from the air. Bacteria in the soil and in plant roots help change nitrogen into a form that plants can use.
- Oxygen is needed by humans and animals to breathe. Green plants produce oxygen during photosynthesis, helping to keep the amount of oxygen in the air constant.
5. What are the other gases present in the atmosphere in small amounts?
Besides nitrogen and oxygen, the atmosphere also contains carbon dioxide, helium, ozone, argon, and hydrogen in smaller quantities. There are also tiny dust particles in the air.
6. How do plants use nitrogen, and why can't they take it directly from the air?
Plants need nitrogen for survival, but they cannot take it directly from the air. Bacteria in the soil and in the roots of some plants take nitrogen from the air and change its form so that plants can use it.
7. How is the balance of oxygen maintained in the atmosphere?
The balance of oxygen in the air is maintained as green plants produce oxygen during photosynthesis and humans and animals use oxygen while breathing. This cycle helps keep the oxygen level constant. Cutting trees can disturb this balance.
8. What is the role of carbon dioxide in the atmosphere?
Carbon dioxide is used by green plants to make food and in the process, they release oxygen. Humans and animals release carbon dioxide when they breathe out. Usually, the amount of carbon dioxide released and used stays balanced.
9. How is the balance of carbon dioxide disturbed, and what are the results?
The balance of carbon dioxide is disturbed when fuels like coal and oil are burned. This adds billions of tons of carbon dioxide to the atmosphere each year, which affects the earth's weather and climate.
10. What will happen if the atmosphere does not exist?
If the atmosphere did not exist, we would not have air to breathe. Also, without the protection of the atmosphere, the heat from the sun would make the earth extremely hot during the day and freezing cold at night, making life impossible.
11. What are the tiny particles present in air besides gases?
Besides gases, tiny dust particles are also present in the air.
12. Why is cutting trees harmful for the balance of gases in the atmosphere?
Cutting trees is harmful because it reduces the number of plants available to produce oxygen and use carbon dioxide. This disturbs the balance of gases in the atmosphere.
Air Circulation
1. What happens to air when it is heated?
When air is heated, it expands, becomes lighter, and rises up.
2. What happens to cold air?
Cold air is denser and heavier, so it tends to sink down.
3. Why does hot air rise and cold air sink?
Hot air rises because it becomes light after expanding. Cold air sinks because it is heavy and dense.
4. What causes air circulation?
Air circulation is caused when hot air rises and cold air moves in to take its place. This movement of air creates air circulation.
5. How does cold air fill in the gap left by hot air?
When hot air rises up, a gap is left behind. Cold air from the surrounding area rushes in to fill the gap, creating movement of air.
6. What is air circulation?
Air circulation is the movement of air caused by hot air rising and cold air coming in to take its place.
7. Why is cold air called “denser”?
Cold air is called denser because its particles are packed closer together, making it heavier than hot air.
8. What is the difference between hot air and cold air?
Hot air: Expands, becomes light, and rises.
Structure of the Atmosphere
1. How many layers does the atmosphere have?
The atmosphere has five layers, starting from the Earth's surface.
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere
- Exosphere
2. What is the name of the lowest layer of the atmosphere?
The lowest layer of the atmosphere is called the Troposphere.
3. What is the average height of the troposphere?
The average height of the troposphere is about 13 km.
4. Why is the troposphere important?
The troposphere is important because:
- We breathe the air that exists in this layer.
- All weather phenomena like rainfall, fog, and hailstorms occur here.
5. What is the second layer of the atmosphere?
The second layer above the troposphere is the Stratosphere.
6. What is the height of the stratosphere?
The stratosphere extends up to about 50 km above the Earth's surface.
7. Why is the stratosphere suitable for flying airplanes?
The stratosphere is suitable for flying airplanes because it is almost free from clouds and weather disturbances, making the air more stable.
8. What important gas layer is found in the stratosphere?
The ozone layer is found in the stratosphere. It protects us from the harmful rays of the sun.
9. What is the third layer of the atmosphere?
The third layer is the Mesosphere.
10. What is the height of the mesosphere?
The mesosphere lies above the stratosphere and extends up to 80 km.
11. What happens in the mesosphere?
In the mesosphere, meteorites burn up when they enter from space.
12. What is the fourth layer of the atmosphere?
The fourth layer is the Thermosphere.
13. What is special about temperature in the thermosphere?
In the thermosphere, the temperature increases very rapidly with height.
14. What is the ionosphere?
The ionosphere is a part of the thermosphere. It lies between 80 to 400 km above the earth.
15. How does the ionosphere help in communication?
The ionosphere helps in radio transmission. It reflects radio waves back to the earth, allowing them to travel long distances.
16. What is the fifth and outermost layer of the atmosphere?
The outermost layer is the Exosphere.
17. What type of gases are found in the exosphere?
The exosphere contains very thin air. It has light gases like helium and hydrogen, which can float into space.
18. Write the names of all the layers of the atmosphere in order from the earth’s surface.
The five layers of the atmosphere from the earth’s surface in order are:
- Troposphere
- Stratosphere
- Mesosphere
- Thermosphere
- Exosphere
19. In which layer of the atmosphere do weather changes like rainfall and fog occur?
Weather changes like rainfall, fog, and hailstorms occur in the troposphere.
20. In which layer do meteorites burn up?
Meteorites burn up in the mesosphere when they enter the earth’s atmosphere from space.
21. Why is the exosphere called the outermost layer of the atmosphere?
The exosphere is called the outermost layer because it is the last layer where the atmosphere merges into outer space.
22. Which layer helps in reflecting radio waves back to earth and what is this part called?
The thermosphere, specifically its ionosphere part, helps in reflecting radio waves back to earth, making radio communication possible.
23. What happens to meteorites as they enter the earth’s atmosphere?
Most meteorites burn up in the mesosphere due to friction with air when entering the earth’s atmosphere.
24. Why does the temperature increase quickly in the thermosphere?
The temperature in the thermosphere increases quickly because it receives direct and intense sunlight and absorbs a lot of energy from the sun.
25. Which gases are common in the exosphere, and what happens to them?
Light gases like helium and hydrogen are common in the exosphere. These gases sometimes escape into space because the air is so thin.
26. What is the main feature of the stratosphere that makes it different from the troposphere?
The stratosphere is mainly free from clouds and weather changes, unlike the troposphere where weather changes occur.
27. Why do airplanes prefer to fly in the stratosphere?
Airplanes prefer to fly in the stratosphere because the air is stable and almost free from clouds and weather disturbances, which makes the flight smoother.
28. What is the height range of the thermosphere?
The thermosphere lies between 80 km and 400 km above the earth's surface.
29. What happens to the temperature in the thermosphere as height increases?
In the thermosphere, the temperature increases very quickly with height.
30. Which part of the thermosphere helps in radio transmission?
The ionosphere, which is a part of the thermosphere, helps in radio transmission.
31. How does the ionosphere help in radio communication?
The ionosphere reflects radio waves that are sent from the earth back to the ground. This helps the radio signals travel long distances.
32. What is the uppermost layer of the atmosphere called?
The uppermost layer is called the exosphere.
33. What kind of air is found in the exosphere?
The exosphere has very thin air, much thinner than any other layer.
34. Which gases are found in the exosphere?
The exosphere contains light gases like helium and hydrogen.
35. What happens to the gases in the exosphere?
Light gases like helium and hydrogen in the exosphere can float into space from this layer.
Weather and Climate
1. What is weather?
Weather is the hour-to-hour or day-to-day condition of the atmosphere. It includes things like temperature, rainfall, wind, humidity, and sunshine.
2. How often can weather change?
Weather can change quickly and dramatically, sometimes within a few hours or by the next day.
3. How does weather affect our mood or behaviour?
- Hot or humid weather can make a person feel uncomfortable or irritable.
- Pleasant, cool, or breezy weather can make someone feel happy or cheerful and even encourage them to plan outdoor activities.
4. What is meant by climate?
Climate is the average weather condition of a place recorded over a longer period of time (usually 30 years or more).
5. How is climate different from weather?
- Weather changes daily or even hourly.
- Climate is the long-term average weather of a place over many years.
6. Why do we check or hear daily weather forecasts?
We check daily weather forecasts to know what the weather will be like in the coming hours or days. This helps people plan their daily activities, travel, sports events, etc.
7. What are weather forecasts used for in daily life? Give an example.
Weather forecasts help us prepare for the weather. For example, cricket fans may check the weather to see if a One Day match might be cancelled due to rain.
8. What is a fun way to understand how weather affects us, as described in the passage?
In the passage, it is described that if our body is like a radio and our mind is its speaker, then weather is like the hand turning the control knob — it changes how we feel or behave!
9. How much of the sun's energy does the earth receive?
The earth receives only 1 part out of 2,000,000,000 (two billion) parts of the sun’s total energy.
10. What activity can you do to study weather changes?
You can note down the daily weather report from a local newspaper for ten days and observe the changes that occur in the weather.
11. What might happen if no one gave or checked weather forecasts?
If no weather forecasts were available, people wouldn’t be prepared for rain, storms, or heatwaves, which could cause damaged crops, travel problems, or health risks.
Temperature
1. What is temperature?
Temperature is the degree of hotness or coldness of the air. It tells us how hot or cold the atmosphere is.
2. What causes the air temperature to change?
The main factor that causes changes in air temperature is insolation — the amount of solar energy (sunlight) received by the earth.
Other reasons include:
Other reasons include:
- Time of day (day is warmer, night is cooler)
- Seasons (summer is hotter, winter is colder)
- Location (places near the equator are warmer than the poles)
3. What is insolation?
Insolation is the incoming solar energy that is received by the earth from the sun.
4. How does insolation affect temperature?
Insolation is not the same everywhere — it decreases from the equator to the poles. So, the equator is warmer, and the poles are colder. This is why areas near the poles are covered with snow.
5. Why is temperature in cities higher than that of villages?
Cities are hotter because:
- Buildings made of concrete and metal get heated during the day.
- Asphalt roads absorb heat and release it at night.
- Tall buildings trap warm air.
6. What is the standard unit for measuring temperature?
The standard unit is degree Celsius (°C).
7. Who invented the Celsius scale?
Anders Celsius invented the Celsius scale.
8. At what temperature does water freeze and boil on the Celsius scale?
- Water freezes at 0°C
- Water boils at 100°C
9. What are some instruments used to measure weather conditions?
Here are some weather instruments and what they measure:
- Thermometer – measures temperature
- Barometer – measures atmospheric pressure
- Rain Gauge – measures amount of rainfall
- Wind Vane – shows the direction of the wind
10. How can rising temperatures affect crops?
If the earth’s temperature rises too high, it can become too warm for some crops to grow, which may harm agriculture.
Air Pressure
1. What is air pressure?
Air pressure is the pressure exerted by the weight of air on the Earth's surface.
2. Why don’t we feel the air pressure on our body?
We don’t feel air pressure because the air presses us from all directions, and our body also pushes back by exerting an equal counter pressure, which is called blood pressure. This balance between the air pressure and our blood pressure keeps us from feeling the pressure on our body.
3. At which place is air pressure highest?
Air pressure is highest at sea level.
4. What happens to air pressure as we go higher up in the atmosphere?
As we go higher up in the atmosphere, the air pressure decreases rapidly.
5. What causes the distribution of air pressure to change horizontally?
The temperature of air at a place affects the horizontal distribution of air pressure.
6. What happens to air in areas with high temperature?
In areas with high temperature, the air gets heated and rises, creating a low-pressure area.
7. What kind of weather is usually found in low-pressure areas?
Low-pressure areas are usually associated with cloudy skies and wet weather.
8. What happens to air in areas with low temperature?
In cooler areas, air becomes cold and heavy, so it sinks and forms a high-pressure area.
9. What kind of weather is usually found in high-pressure areas?
High-pressure areas are usually associated with clear and sunny skies.
10. In which direction does air move?
Air always moves from high-pressure areas to low-pressure areas.
11. Why do astronauts wear special suits on the moon?
On the moon, there is no air and no air pressure, so astronauts must wear special space suits filled with air to protect their bodies.
12. What would happen if astronauts did not wear space suits?
If astronauts didn’t wear space suits, the counter pressure from their body would make their blood vessels burst, and they would bleed.
13. Why do mountain climbers find it harder to breathe at high altitudes?
At high altitudes, air pressure is lower, so there is less oxygen in the air, making it harder to breathe.
Wind and Cyclones
1. What is wind?
Wind is the movement of air from a high pressure area to a low pressure area.
2. How can you see or feel the presence of wind?
- Wind blows dry leaves down the road.
- It can uproot trees during a storm.
- Gentle wind blows away smoke or fine dust.
- Strong winds make it hard to walk or to hold an umbrella outside.
3. What problems can strong winds create?
- Uproot or break trees
- Damage or blow away roofs of houses and sheds
- Make it difficult to walk or bike
- Cause problems for people using umbrellas or carrying light objects
4. How are winds named?
A wind is named from the direction it comes from. For example, wind blowing from the west is called a westerly.
5. Into how many types can winds be broadly divided? Name them.
Winds are broadly divided into three types:
- Permanent winds
- Seasonal winds
- Local winds
6. What are permanent winds? Give examples.
- Permanent winds blow constantly throughout the year in a specific direction.
- Examples: Trade winds, westerlies, and easterlies.
7. What are seasonal winds? Give an example.
- Seasonal winds change their direction in different seasons.
- Example: Monsoons in India.
8. What are local winds? Give examples.
- Local winds blow only during a particular period of the day or year in a small area.
- Examples: Land breeze, sea breeze, and the hot dry "loo" of northern India.
9. What is a cyclone?
A cyclone is a violent storm with very strong winds, often causing damage and usually followed by heavy rain and sea surges.
10. Describe the effects of the supercyclone that hit Odisha in October 1999.
- Cyclone winds reached up to 260 km per hour and lasted for over 36 hours.
- Trees and kutcha houses were uprooted and destroyed.
- Roofs of industrial sheds and houses were blown away.
- Power supply and communication lines were snapped.
- Heavy rain for three days caused rivers to flood.
- Tidal waves of 7 to 10 meters high swept 20 km inland, damaging crops.
- Approximately 13 million people were affected.
- Many animals died; huge damage to crops (paddy, vegetables, fruit).
- Salinisation from tidal water made agricultural land infertile.
- Large areas of forest (sal, teak, bamboo, mangroves) disappeared.
11. How does a cyclone form?
- A cyclone can start as a depression (low-pressure area) over the sea (like the Gulf of Thailand).
- It moves, gains strength, and can become a supercyclone before hitting land.
12. Name three factors that caused damage during the Odisha supercyclone.
- Wind velocity (speed)
- Heavy rainfall
- Tidal surge (big waves from the sea)
13. What is the impact of tidal surges during a cyclone?
- Tidal surges can flood coastal areas very quickly.
- Bring salty water far inland, which damages or kills crops and plants.
- Make the soil salty and infertile.
14. What happens to forests during powerful cyclones?
- Large tracts of forests, such as sal, teak, bamboo, and mangroves, can be destroyed or completely vanish.
15. Why are cyclones common in places like Odisha?
Odisha is on the eastern coast of India, close to the Bay of Bengal where cyclones often originate and grow strong over the sea before hitting land.
Moisture and Rainfall
1. What is moisture in the air called?
Moisture in the air is called humidity.
2. What is humidity?
Humidity is the amount of water vapour present in the air at any given time.
3. What is a humid day?
A humid day is when the air is full of water vapour, making it feel very sticky and uncomfortable.
4. What happens to the air’s capacity to hold water vapour as it gets warmer?
As the air becomes warmer, its capacity to hold water vapour increases, so it becomes more humid.
5. Why do we feel sticky and uncomfortable on a humid day?
On a humid day:
- Sweat does not evaporate easily from our body.
- Clothes take longer to dry, making us feel sticky and hot.
6. How are clouds formed?
When water vapour rises, it cools and condenses to form tiny water droplets. These droplets gather to form clouds.
7. What is precipitation?
Precipitation is when water droplets in the clouds become too heavy and fall to the earth. It includes rain, snow, sleet, or hail.
8. What is rain?
Rain is the precipitation that comes down to the earth in liquid form.
9. What causes jet planes to leave a white trail in the sky?
The moisture released from the engines of jet planes condenses in the cold upper air, forming white trails, which are visible when there is no wind to disturb them.
10. What are the different types of rainfall based on the mechanism?
The three main types of rainfall are:
- Convectional Rainfall
- Relief (Orographic) Rainfall
- Cyclonic Rainfall
11. What is convectional rainfall?
Convectional rainfall occurs when the sun heats the ground, causing warm moist air to rise. The air cools and condenses, bringing rain.
12. What is orographic (relief) rainfall?
Orographic rainfall occurs when moist air hits a mountain, rises, cools, and causes rainfall on the windward side.
13. What is cyclonic rainfall?
Cyclonic rainfall occurs when warm moist air meets cold air, creating a low-pressure system that causes heavy rain.
14. Why is rainfall important?
Rainfall is important because:
- It brings fresh water to the earth.
- It helps in the growth of plants and survival of animals.
- Most groundwater comes from rainwater.
15. What problems happen when there is too little or too much rainfall?
- Too little rainfall causes water scarcity and drought.
- Too much rainfall causes floods.
16. How do plants help in preserving water?
Plant roots hold soil and water. When trees are present, they help retain rainwater and stop it from flowing away quickly.
17. What happens when trees on hillsides are cut down?
If trees on hills are cut:
- Rainwater flows down quickly,
- Flooding may occur in low-lying areas,
- Soil erosion increases
18. Name some other forms of precipitation besides rainfall.
Other forms of precipitation are: Snow, Sleet, Hail
19. What is the difference between snow, sleet and hail?
| Type | What Is It? | How It Feels & Looks When It Happens |
|---|---|---|
| Snow | Soft, white flakes | Light, fluffy, and cold; looks like feathers. When weather is very cold (below 0°C), usually in winter. |
| Sleet | Small ice pellets | Hard, tiny balls of ice; bounces when it falls. When rain passes through a layer of freezing air and freezes before hitting the ground. |
| Hail | Hard, round ice balls | Larger, hard balls of ice; can be loud and even hurt if they hit you! During strong storms, often in summer, with thunder and lightning. |
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