Class 11 Geography - MAHARASHTRA
Composition and Structure of Atmosphere
The chapter 'Composition and Structure of Atmosphere' for Class 11 Maharashtra State Board students explores the envelope of air surrounding the Earth. It covers the primary gases, water vapour, and dust particles that make up the atmosphere, along with their geographical significance. Students will learn about the vertical layering of the atmosphere—troposphere, stratosphere, mesosphere, thermosphere, and exosphere—based on temperature variations. Understanding this chapter is crucial for board exams as it forms the foundation for climatology, explaining weather phenomena, atmospheric pressure belts, and global temperature distribution.
Start Learning FreeKey Concepts
Composition of the Atmosphere
The atmosphere is made up of permanent gases like nitrogen (78%) and oxygen (21%), variable gases like carbon dioxide and ozone, water vapour, and solid dust particles.
Structure of the Atmosphere (Layers)
The atmosphere is vertically divided into five distinct layers—troposphere, stratosphere, mesosphere, thermosphere, and exosphere—based on changing temperature characteristics.
Troposphere
The lowest layer of the atmosphere where all weather phenomena occur, and temperature decreases with an increase in altitude at the normal lapse rate.
Stratosphere
The layer above the troposphere containing the ozone layer, which absorbs harmful ultraviolet rays from the Sun and causes temperatures to increase with altitude.
Normal Lapse Rate
The rate at which air temperature decreases with increasing altitude in the troposphere, which is approximately 6.5°C per 1,000 meters.
Important Formulas
Board Exam Info
In the Maharashtra (MSBSHSE) Class 11 Geography board-pattern exams, this chapter typically carries about 5 to 7 marks. Common question types include short answer questions on the structure of the atmosphere, distinguish between layers (like troposphere and stratosphere), diagram-based questions requiring the labeling of atmospheric layers, and objective questions on gas percentages.
Frequently Asked Questions
Why does temperature decrease with height in the troposphere?
The troposphere is heated from below by terrestrial radiation (heat radiated from the Earth's surface) rather than directly by the Sun, so air gets colder as you move further away from the surface.
What is the significance of the ozone layer in the stratosphere?
The ozone layer absorbs harmful ultraviolet (UV) radiation coming from the Sun, protecting life on Earth from skin cancer, eye damage, and ecological disruptions.
Are dust particles in the atmosphere useful?
Yes, dust particles act as hygroscopic nuclei (condensation nuclei) around which water vapour condenses to form clouds, fog, and precipitation, and they also help scatter sunlight, causing dawn and twilight.
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