Composition and Structure of Atmosphere
NCERT Solutions • Class 11 Geography • Chapter 71. Multiple Choice Questions
(i) Which one of the following gases constitutes the major portion of the atmosphere?
(b) Nitrogen
Reason: Nitrogen makes up approximately 78.08% of the total volume of the atmosphere, followed by Oxygen at 20.95%.
Reason: Nitrogen makes up approximately 78.08% of the total volume of the atmosphere, followed by Oxygen at 20.95%.
(ii) Atmospheric layer important for human beings is:
(c) Troposphere
Reason: All weather phenomena (rainfall, clouds, storms) occur here, and it contains the air we breathe.
Reason: All weather phenomena (rainfall, clouds, storms) occur here, and it contains the air we breathe.
(iii) Sea salt, pollen, ash, smoke soot, fine soil — these are associated with:
(b) Dust particles
Reason: These are solid particles suspended in the air, acting as hygroscopic nuclei around which water vapour condenses to form clouds.
Reason: These are solid particles suspended in the air, acting as hygroscopic nuclei around which water vapour condenses to form clouds.
(iv) Oxygen gas is in negligible quantity at the height of atmosphere:
(b) 120 km
Reason: Oxygen becomes negligible at altitudes of 120 km, while carbon dioxide and water vapour are found only up to 90 km.
Reason: Oxygen becomes negligible at altitudes of 120 km, while carbon dioxide and water vapour are found only up to 90 km.
(v) Which one of the following gases is transparent to incoming solar radiation and opaque to outgoing terrestrial radiation?
(d) Carbon dioxide
Reason: This property creates the Greenhouse Effect, trapping heat near the earth’s surface.
Reason: This property creates the Greenhouse Effect, trapping heat near the earth’s surface.
2. Short Answer Questions
(i) What do you understand by atmosphere?
The atmosphere is a vast expanse of air that surrounds the earth on all sides, held to it by the force of gravity. It acts as a protective blanket, shielding life from harmful UV rays and regulating the planet’s temperature.
(ii) What are the elements of weather and climate?
The main elements are:
- Temperature: Degree of hotness or coldness.
- Pressure: Atmospheric weight.
- Wind: Moving air.
- Humidity: Moisture content.
- Clouds & Precipitation: Rainfall, snow, etc.
(iii) Describe the composition of atmosphere.
The atmosphere is a mixture of:
- Gases: Nitrogen (78%), Oxygen (21%), Argon (0.93%), Carbon Dioxide (0.03%), and traces of Neon, Helium, Ozone, etc.
- Water Vapour: Variable gas (0-4%) essential for weather.
- Dust Particles: Solid particulate matter (salt, ash, pollen).
(iv) Why is troposphere the most important of all the layers of the atmosphere?
It is the most important because:
- It contains the air we breathe.
- All weather phenomena (rain, fog, hailstorm) occur in this layer.
- It supports biological life on the earth’s surface.
3. Long Answer Questions
(i) Describe the composition of the atmosphere.
The atmosphere is composed of gases, water vapour, and dust particles.
1. Gases:
1. Gases:
- Nitrogen (78%) & Oxygen (21%): Make up 99% of clean, dry air. Oxygen is vital for breathing; Nitrogen acts as a diluent and is essential for plants.
- Carbon Dioxide ($CO_2$): Very small percentage (0.03%) but meteorologically crucial. It is transparent to incoming solar radiation but opaque to outgoing terrestrial radiation, causing the Greenhouse Effect.
- Ozone ($O_3$): Found in the stratosphere (10-50 km). It acts as a shield, absorbing harmful Ultraviolet (UV) rays from the sun.
- It is a variable gas, decreasing with altitude and from the equator towards the poles.
- It absorbs parts of the insolation from the sun and preserves earth’s radiated heat, acting like a blanket.
- Includes sea salts, fine soil, smoke-soot, ash, pollen.
- They act as hygroscopic nuclei around which water vapour condenses to produce clouds.
(ii) Draw a suitable diagram for the structure of the atmosphere and label it and describe it.
[Image of layers of atmosphere diagram]
The atmosphere consists of five distinct layers based on temperature variation:
1. Troposphere:
The atmosphere consists of five distinct layers based on temperature variation:
1. Troposphere:
- Lowest layer; average height 13 km (8 km at poles, 18 km at equator).
- Temperature decreases with height (Normal Lapse Rate: 1°C per 165m).
- Contains dust particles and water vapour; all weather changes happen here.
- Extends up to 50 km.
- Contains the Ozone layer which absorbs UV rays.
- Free from weather disturbances, making it ideal for flying jet aircraft.
- Extends up to 80 km.
- Coldest layer; temperature drops to -100°C.
- Meteorites burn up in this layer.
- Located between 80-400 km.
- Contains electrically charged particles known as ions.
- Radio waves transmitted from earth are reflected back by this layer.
- The uppermost layer; gradually merges with outer space.
- Extremely rarefied air (light gases like helium and hydrogen float here).