COMPOSITION AND STRUCTURE-ATMOSPHERE
What is meant by the composition of the atmosphere? Name the main gases present in the atmosphere.
The composition of the atmosphere refers to the different gases present in the air and the proportion in which they occur.
Nitrogen
Oxygen
Argon
Carbon dioxide
Small amounts of other gases like neon, helium, and water vapour are also present.
Name the different layers of the atmosphere
Troposphere:
Stratosphere:
Mesosphere:
Thermosphere:
Exosphere:
Define wind. Name any two types of winds.
Wind is the movement of air from a region of high pressure to a region of low pressure.
Two types of winds:
Permanent winds (e.g., Trade Winds)
Local winds (e.g., Land and Sea Breezes)
Define air pressure.
Define temperature
Air Pressure: The force exerted by the weight of air on the surface of the Earth.
Measure of degree of hotness or coldness of a place.
Commercial airplanes usually fly in the lower part of the stratosphere rather than in the troposphere. Using your knowledge of the structure of the atmosphere, explain why this layer is more suitable for air travel.
The stratosphere has stable air conditions with very little weather disturbance.
There are fewer clouds, storms, and turbulence compared to the troposphere.
How does the mesosphere help in protecting life on Earth? Explain in points.
The mesosphere burns up most meteors due to friction, preventing them from reaching Earth.
By absorbing and burning meteors, it helps maintain a safe environment for life on Earth.
Explain what seasonal winds are and how they affect the climate and life in different parts of India. Give examples.
Seasonal winds are winds that change their direction with the seasons.
Monsoon winds are an example:
Southwest monsoon (summer) brings heavy rainfall to India, helping in agriculture.
Northeast monsoon (winter) is dry in most parts of India but brings rain to Tamil Nadu and southeast coast.
How does temperature affect air pressure?
Effect of Temperature on Air Pressure:
High temperature → air expands → air becomes lighter → low air pressure.
Low temperature → air contracts → air becomes denser → high air pressure.
Oxygen forms only about 21% of the atmosphere, yet it is essential for most living organisms. Why would an increase or decrease in the percentage of oxygen disturb life on Earth?
A decrease in oxygen would make breathing difficult for humans and animals.
An increase in oxygen could lead to frequent and intense fires, as oxygen supports burning.
The balance of gases in the atmosphere is necessary to maintain stable life conditions.
If the thermosphere did not contain ionised gases, how would modern communication and space activities be affected? Explain.
Long-distance radio communication would be disrupted because ionised gases help reflect radio waves.
Satellite communication systems such as GPS and weather monitoring would become less effective.
In a coastal town, people notice that during the day, strong winds blow from the sea toward the land, and at night, the direction reverses. Farmers say these winds affect their crops, and fishermen use them to plan their work. Analyze the situation and answer the following:
Identify the type of local wind described.
Explain why these winds change direction between day and night.
Type of wind:
These are local winds, specifically Sea Breeze (day) and Land Breeze (night).
2. Reason for direction change:
During the day: Land heats up faster than sea → air above land rises → cooler air from sea moves toward land → Sea Breeze.
During the night: Land cools faster than sea → air above sea rises → cooler air from land moves toward sea → Land Breeze.
Ravi, a student, noticed that during summer, some parts of India experience strong winds and very hot weather, while during winter, the same regions feel very cold and calm. He wants to understand why these changes occur.
Tasks:
Explain how temperature differences lead to changes in air pressure.
Describe how these changes in air pressure cause winds to blow.
Temperature differences and air pressure:
Land and air heat up faster than water during summer → air above land becomes lighter → low pressure.
Land cools faster than water during winter → air above land becomes denser → high pressure.
2. Air pressure and wind formation:
Air always moves from high-pressure areas to low-pressure areas.
This movement of air is experienced as wind.
Carbon dioxide is present in a very small amount in the atmosphere. How can an increase in this small percentage affect Earth’s temperature and climate patterns?
Increased carbon dioxide traps more heat, leading to global warming.
It can cause changes in rainfall patterns and increase extreme weather events.
Rising temperatures can affect ecosystems, agriculture, and human life.
Scientists have observed that the Earth's average temperature is gradually increasing due to excessive greenhouse gases. If these gases were completely removed from the atmosphere, what changes would you expect in the Earth’s climate and life on it? Explain your reasoning.
Without greenhouse gases, the Earth would become extremely cold, as heat from the Sun would escape back into space.
Average global temperature would drop, making survival difficult for many plants, animals, and humans.
Natural greenhouse effect is essential for maintaining life-friendly temperatures; removing it entirely would disrupt ecosystems.
India experiences different types of winds, including permanent, seasonal, and local winds. Imagine you are a weather expert preparing a report for farmers, fishermen, and city planners.
Tasks:
Classify the winds of India into permanent, seasonal, and local winds, giving examples of each.
Explain how each type of wind affects agriculture, water resources, and daily life.
Suggest measures that people can take to benefit from favorable winds and minimize harm from harmful winds.
Classification of winds:
Permanent winds: Blow throughout the year.
Example: Trade Winds, Westerlies, Polar Easterlies.
Seasonal winds: Change direction with seasons.
Example: Southwest Monsoon (summer), Northeast Monsoon (winter).
Local winds: Blow over a small area and last for a short duration.
Example: Sea Breeze, Land Breeze, Loo, Mountain Breeze, Valley Breeze
Permanent winds: Indirectly influence rainfall and agricultural productivity.
Seasonal winds: Brings rainfall essential for crops like rice, sugarcane, and wheat.
Local winds:
Sea and Land Breezes: Help fishermen and farmers plan work.
Plant crops according to seasonal wind patterns; use windbreaks to protect crops.
Plan trips based on sea and land breezes.
During summer, some coastal areas experience strong sea breezes, while inland areas feel extremely hot and dry. In winter, the situation reverses, and the winds come from the land toward the sea. Analyze the situation and answer the following:
Explain why the direction of the wind changes between day and night or between seasons.
How are these changes related to temperature and air pressure differences?
Direction of winds:
Daytime / Summer: Land heats up faster → air above land rises → low pressure over land → cooler air from sea moves toward land → sea breeze.
Relation to temperature and air pressure:
High temperature → air expands → low air pressure.
Low temperature → air contracts → high air pressure.
Winds always blow from high-pressure areas to low-pressure areas.