Class 11 Geography - CBSE
Composition and Structure of Atmosphere
The chapter 'Composition and Structure of Atmosphere' explores the blanket of gases surrounding the Earth, vital for sustaining life. Class 11 CBSE students study the permanent and variable gases like nitrogen, oxygen, and carbon dioxide, alongside water vapour and dust particles. The chapter details the vertical structure of the atmosphere, dividing it into five distinct layers: 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, global warming, and the greenhouse effect, frequently fetching direct and analytical questions.
Start Learning FreeKey Concepts
Composition of the Atmosphere
The atmosphere is made up of three components: gases, water vapour, and dust particles. Nitrogen (78.08%) and Oxygen (20.95%) make up the bulk of permanent gases.
Structure of the Atmosphere
The atmosphere is divided into layers based on temperature conditions: Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere.
Troposphere
The lowest and most dense layer of the atmosphere where all weather changes occur, and temperature decreases with increasing height at a rate of 1°C for every 165m.
Stratosphere
The layer above the troposphere that contains the ozone layer, which absorbs harmful ultraviolet rays, and where temperature increases with height.
Greenhouse Gases
Gases like carbon dioxide, methane, and ozone that are transparent to incoming solar radiation but opaque to outgoing terrestrial radiation, keeping the Earth warm.
Important Formulas
Board Exam Info
In CBSE Class 11 Geography exams, this chapter typically carries around 3 to 5 marks. Questions commonly include direct definitions, short-answer questions differentiating atmospheric layers (especially Troposphere and Stratosphere), and diagram-based or reasoning questions about temperature decrease with height.
Frequently Asked Questions
Why does temperature decrease with height in the troposphere?
Because the troposphere is heated from below by the Earth's surface, which absorbs solar radiation and radiates it back as terrestrial radiation.
What is the difference between weather and climate based on this chapter?
Weather is the day-to-day state of the atmosphere in a specific place (mostly occurring in the troposphere), while climate is the aggregate of weather conditions over a long period, usually 30 years or more.
Why is the ozone layer important and where is it found?
The ozone layer is found in the stratosphere and is crucial because it absorbs harmful ultraviolet (UV) radiation from the sun, protecting life on Earth from skin cancer and other severe health hazards.
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