Class 11 Geography - KARNATAKA
Composition and Structure of Atmosphere
This chapter explores the composition and vertical structure of Earth's atmosphere, which is essential for Class 11 KSEEB Geography students. You will learn about the permanent and variable gases like nitrogen, oxygen, and carbon dioxide, water vapour, and dust particles that make up the air around us. The chapter details the five distinct atmospheric layers—troposphere, stratosphere, mesosphere, thermosphere, and exosphere—based on temperature variations. Understanding this chapter is crucial for board exams as it forms the foundational basis for upcoming topics on weather, climate, and insolation, frequently appearing in both short and descriptive question formats.
Start Learning FreeKey Concepts
Composition of the Atmosphere
The atmosphere is made up of gases, water vapour, and dust particles. Nitrogen (78.08%) and Oxygen (20.95%) make up the bulk of permanent gases, while carbon dioxide and ozone play vital roles in regulating heat and absorbing harmful UV radiation.
Troposphere
This is the lowest and densest layer of the atmosphere where all weather phenomena take place. Temperature decreases with increasing height at a normal lapse rate of 1°C for every 165 meters.
Stratosphere
Found above the troposphere, this layer contains the ozone layer which absorbs harmful ultraviolet rays from the Sun. It is ideal for flying jet aircraft because it is free from clouds and weather disturbances.
Mesosphere
Located above the stratosphere, this is the coldest layer of the atmosphere where temperatures drop down to -90°C. Meteors burn up upon entering this layer due to friction with gas molecules.
Thermosphere and Exosphere
The thermosphere contains electrically charged ions known as the ionosphere that reflect radio waves back to Earth. The exosphere is the outermost layer where the atmosphere merges into outer space.
Important Formulas
Board Exam Info
In the Karnataka (KSEEB) Class 11 Geography annual examinations, this chapter typically carries around 4 to 6 marks. Common question types include 1-mark objective questions, 2-mark definitions (like the normal lapse rate or ozone layer), and 5-mark descriptive questions asking to explain the structure of the atmosphere with a labelled diagram.
Frequently Asked Questions
Why does temperature decrease with height in the troposphere?
The troposphere is heated from below by terrestrial radiation (heat radiated from Earth's surface) rather than directly by the Sun, so air gets colder as you move farther away from the heat source.
What is the importance of the ozone layer in the stratosphere?
The ozone layer absorbs harmful ultraviolet (UV) radiation coming from the Sun, protecting living organisms on Earth from skin cancer, blindness, and DNA damage.
Why do meteors burn up in the mesosphere?
Even though the air is very thin in the mesosphere, it is dense enough to create friction against fast-moving meteors, causing them to heat up and burn completely before hitting Earth's surface.
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