Looking for an exam-oriented collection of extra questions and answers for SEBA Class 9 Social Science Geography Chapter 2 (Atmosphere: Structure, Air Pressure and Wind System / বায়ুমণ্ডল: গঠন, বায়ুৰ চাপ আৰু বায়ু প্ৰবাহ) for the 2026–27 academic session? Access thoroughly solved Short Answer Questions (2–3 marks), Long Analytical Questions (4–5 marks), comparative distinction tables, and atmospheric diagrams. Master high-yield exam topics covering the vertical thermal structure of the atmosphere (Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere); normal lapse rate and the ozonosphere; global air pressure belts (Equatorial Low Pressure Belt/Doldrums, Subtropical High Pressure Belts/Horse Latitudes, Subpolar Lows, and Polar Highs); factors controlling atmospheric pressure; planetary wind systems (Trade Winds, Westerlies, and Polar Easterlies); Ferrel’s Law and Coriolis Effect; periodic winds including land and sea breezes, mountain and valley breezes, and monsoon winds; local winds (Loo, Chinook, Foehn, Mistral); mechanisms and structural differences between tropical cyclones and extra-tropical temperate cyclones; and anticyclones, structured strictly according to the Assam Board (SEBA) examination pattern.
Q.1. What is the gaseous envelope of air surrounding the earth called?
Answer: Atmosphere
Q.2. Up to what vertical altitude does the earth’s atmosphere extend?
Answer: Around 10,000 km
Q.3. Which natural force keeps the atmosphere attached to the earth?
Answer: Earth’s gravitational force
Q.4. Which gas constitutes the largest volume (78.08%) in the atmosphere?
Answer: Nitrogen
Q.5. What is the volumetric percentage of oxygen in the atmosphere?
Answer: 20.94%
Q.6. What is the percentage of carbon dioxide present in the atmosphere?
Answer: 0.036%
Q.7. Which atmospheric layer extends from the earth’s surface up to about 80 km where the chemical composition remains almost the same?
Answer: Homosphere
Q.8. What is the atmospheric layer above 80 km with varying chemical composition called?
Answer: Heterosphere
Q.9. What is the lowermost layer of the atmosphere touching the earth’s surface?
Answer: Troposphere
Q.10. What is the average vertical height of the troposphere?
Answer: 12 km
SEBA Class 9 Geography Chapter 2 Extra Questions
Q.11. What is the rate of decrease of temperature with increasing height in the troposphere called?
Answer: Lapse Rate
Q.12. What is the normal value of the lapse rate per kilometre of ascent?
Answer: 6.5°C per km
Q.13. What is the boundary line separating the troposphere and the stratosphere called?
Answer: Tropopause
Q.14. Which specific gas found in the stratosphere absorbs harmful solar ultraviolet rays?
Answer: Ozone
Q.15. What is the uppermost boundary of the stratosphere called?
Answer: Stratopause
Q.16. In which atmospheric layer does the temperature drop to a minimum of about -100°C?
Answer: Mesosphere
Q.17. Which layer of the atmosphere contains electrically charged ions and reflects radio waves?
Answer: Ionosphere (or Thermosphere)
Q.18. What is the outermost layer of the atmosphere extending from 400 km up to 10,000 km?
Answer: Exosphere
Q.19. Which instrument is used to measure atmospheric pressure?
Answer: Barometer
Q.20. What is the standard atmospheric pressure at sea level measured in millibars (mb)?
Answer: 1013.2 mb
Atmosphere Structure Air Pressure and Wind System Important Questions 2026-27
Q.21. What is the normal height of the mercury column at sea level in inches?
Answer: 29.92 inches (or 76 cm)
Q.22. What is horizontal air movement parallel to the earth’s surface called?
Answer: Wind
Q.23. What is vertical air movement called?
Answer: Air current
Q.24. What is the calm equatorial low pressure belt situated between 10° N and 10° S called?
Answer: Doldrums
Q.25. What is the sub-tropical high pressure belt located between 25° and 35° latitudes historically called?
Answer: Horse Latitudes
Q.26. Which scientific law explains that winds deflect to the right in the Northern Hemisphere and to the left in the Southern Hemisphere?
Answer: Ferrel’s Law
Q.27. Where is the Coriolis force equal to zero on the earth?
Answer: At the equator
Q.28. What are the strong, high-velocity upper-tropospheric winds blowing towards the east called?
Answer: Jet Stream
Q.29. What is the line of discontinuity formed when two contrasting air masses meet called?
Answer: Front
Q.30. Who introduced the term ‘Anticyclone’ in the year 1861?
Answer: Sir Francis Galton
Class 9 Social Science Geography Chapter 2 Extra Q&A SEBA
SHORT-ANSWER QUESTIONS AND ANSWERS
Q.1. What is the Biosphere?
Answer: The Biosphere is the life-supporting zone of the earth created by the interaction of the atmosphere, lithosphere, and hydrosphere, providing air, water, and land necessary for living organisms.
Q.2. Why is carbon dioxide important for life on earth despite its low amount?
Answer: Carbon dioxide absorbs heat radiated from the earth’s surface to maintain an average global temperature of 15°C, and plants use it during photosynthesis to make food.
Q.3. What causes Global Warming?
Answer: Global warming is caused by large-scale deforestation and the burning of fossil fuels like coal and petroleum, which increase carbon dioxide levels and trap extra heat in the atmosphere.
Q.4. What is the role of dust particles in the atmosphere?
Answer: Dust particles act as condensation nuclei, allowing water vapour in the air to condense around them to form clouds, fog, and rain.
Q.5. Name the four atomic gas layers present in the Heterosphere according to altitude.
Answer: The four layers arranged by atomic weight are the Nitrogen layer, Oxygen layer, Helium layer, and Hydrogen layer.
Q.6. Why do aeroplanes prefer to fly in the lower stratosphere?
Answer: Aeroplanes fly in the lower stratosphere because this layer is free from clouds, storms, and other violent weather disturbances, offering smooth horizontal air movement.
Q.7. What is atmospheric pressure?
Answer: Atmospheric pressure is the force or weight exerted by the column of air per unit area on the earth’s surface.
Q.8. How does an increase in air temperature affect atmospheric pressure?
Answer: When air temperature rises, the air expands, becomes less dense, and rises upward, resulting in lower atmospheric pressure.
Q.9. How does altitude affect air pressure?
Answer: As altitude increases, the overlying column of air becomes thinner and less dense, causing atmospheric pressure to decrease (about 1 inch or 34 mb for every 900 feet of ascent).
Q.10. Why is the equatorial region characterized by permanent low pressure?
Answer: The equatorial region receives direct vertical sun rays all year, keeping the air hot, light, and full of water vapour, which causes it to rise continuously.
SEBA Class 9 Geography Pressure Belts Planetary Winds Cyclones Notes
Q.11. Why is the sub-polar belt a low pressure zone?
Answer: Due to the earth’s rotation, air from the sub-polar regions is thrown outward and deflected towards the sub-tropics, reducing the volume of air and forming low pressure.
Q.12. Why do polar regions have high atmospheric pressure throughout the year?
Answer: Polar regions receive very little solar heat, making the air extremely cold, dense, and heavy, with almost no moisture, which causes permanent high pressure.
Q.13. What is the basic difference between wind and air current?
Answer: Wind refers to the horizontal movement of air parallel to the earth’s surface, while an air current refers to the vertical upward or downward movement of air.
Q.14. What is Ferrel’s Law?
Answer: Ferrel’s Law states that due to the Coriolis force caused by the earth’s rotation, all moving winds deflect to their right in the Northern Hemisphere and to their left in the Southern Hemisphere.
Q.15. Why are the Westerlies very strong in the Southern Hemisphere?
Answer: Between 40° S and 60° S latitudes, the Southern Hemisphere is covered almost entirely by vast oceans with little land to cause friction, making the Westerlies very strong and constant.
Q.16. What are the Roaring Forties, Furious Fifties, and Screaming Sixties?
Answer: These are nautical names given by sailors to the stormy, powerful Westerly winds blowing across the open oceans of the Southern Hemisphere between 40° and 70° south latitudes.
Q.17. What is an air mass?
Answer: An air mass is a large body of air spreading over hundreds of kilometres that has nearly uniform temperature and moisture characteristics throughout.
Q.18. Name the four primary types of air masses.
Answer: The four main air masses are Tropical Continental (cT), Tropical Maritime (mT), Polar Continental (cP), and Polar Maritime (mP).
Q.19. What is the difference between a cold front and a warm front?
Answer: A cold front occurs when an advancing cold air mass pushes under and displaces warm air, while a warm front occurs when an advancing warm air mass glides up over retreating cold air.
Q.20. What is an Anticyclone?
Answer: An anticyclone is a high-pressure weather system where atmospheric pressure is highest at the center, causing winds to blow outward in a diverging clockwise pattern in the Northern Hemisphere and anticlockwise in the Southern Hemisphere.
LONG QUESTIONS AND ANSWERS (3 MARKS EACH)
Q.1. Describe the key characteristics of the Troposphere.
Answer: 1. It is the lowest atmospheric layer touching the earth’s surface, having an average height of 12 km (16 km at the equator and 8 km at the poles).
2. It contains roughly three-fourths of all atmospheric gases, nearly all water vapour, and dust particles.
3. All weather phenomena like clouds, rainfall, fog, storms, and cyclones take place here, and temperature decreases with height at the lapse rate of 6.5°C per km.
Q.2. Write a short note on the Stratosphere and explain why it is vital for living organisms.
Answer: 1. The stratosphere lies directly above the tropopause and extends up to about 50 km from the earth’s surface.
2. It contains the ozone layer (mainly concentrated between 40 and 50 km), which absorbs dangerous ultraviolet (UV) radiation from the sun, protecting humans, animals, and plants from severe health hazards.
3. Temperature increases from -60°C to about 0°C across this layer due to UV absorption, and its dry, cloud-free conditions make it ideal for flying jet planes.
Q.3. Explain the main characteristics of the Thermosphere (Ionosphere).
Answer: 1. The thermosphere extends from the mesopause at an altitude of 80 km up to roughly 400 km.
2. Temperature rises rapidly with height, reaching up to 1650°C, while air density drops near zero.
3. It contains electrically charged ions, which reflect ground-based radio waves back to the earth, enabling long-distance wireless telecommunication.
Q.4. Explain how temperature and altitude influence atmospheric pressure.
Answer: Effect of Temperature: Heating causes air molecules to expand, turn light, and rise, resulting in low pressure. Cooling contracts air, makes it denser, and causes it to sink, resulting in high pressure.
Effect of Altitude: As height increases, the overlying mass of the atmosphere decreases, which lowers air density. As a result, air pressure drops by roughly 1 inch (34 mb) for every 900 feet of ascent.
Q.5. How are the Sub-Tropical High Pressure Belts formed, and why are they called ‘Horse Latitudes’?
Answer: Formation: Hot air rising from the equator moves toward the poles, cools, becomes heavier, and sinks down around 25° to 35° North and South latitudes, creating sub-tropical high pressure belts with calm, descending air.
Origin of Name: In the age of sailing ships, vessels often got stranded in these calm, windless seas for weeks. To conserve drinking water and lighten ship weight, European sailors threw their horses overboard, leading to the name “Horse Latitudes”.
Assam Board Class 9 Geography Chapter 2 Solved Extra Questions PDF
Q.6. What is Coriolis force? Explain its influence on global wind direction.
Answer: 1. The Coriolis force is an apparent deflecting force produced by the earth’s rotation on its axis.
2. It deflects all moving air to the right of its path in the Northern Hemisphere and to the left of its path in the Southern Hemisphere (Ferrel’s Law).
3. The force is zero at the equator and reaches its maximum value at the poles, controlling the rotational direction of global planetary winds and cyclones.
Q.7. What is a Jet Stream and what is its meteorological significance?
Answer: 1. A Jet Stream is a narrow, fast-flowing current of air moving west-to-east at high speeds (up to 640 km/h) in the upper troposphere.
2. It is generated by strong temperature contrasts between polar and tropical air masses.
3. Jet streams guide surface weather systems, direct cyclonic storms, and significantly influence monsoons and seasonal weather patterns.
Q.8. What is a Front? State the essential conditions required for frontogenesis (formation of a front).
Answer: A front is a boundary zone or surface of discontinuity separating two air masses of contrasting temperature, humidity, and density.
Condition 1: The two meeting air masses must have contrasting physical properties, with one being distinctly colder and denser than the other.
Condition 2: The wind circulation must be convergent, forcing the two air masses to move toward each other so that the lighter warm air is pushed upward over the denser cold air.
Q.9. Distinguish between a Cyclone and an Anticyclone.
Answer: Pressure Structure: A cyclone has an intense low-pressure centre with high pressure outside, whereas an anticyclone has a high-pressure centre with lower pressure outward.
Wind Circulation: In a cyclone, winds blow inward in a convergent spiral (anticlockwise in the Northern Hemisphere, clockwise in the Southern Hemisphere). In an anticyclone, winds blow outward in a divergent pattern (clockwise in the Northern Hemisphere, anticlockwise in the Southern Hemisphere).
Weather Conditions: Cyclones bring thick clouds, heavy rain, and stormy weather, while anticyclones bring dry, calm, and clear skies (fair weather).
Q.10. What is meant by Secondary Circulation? Give examples.
Answer: 1. Secondary circulation refers to regional and seasonal wind systems caused by temperature differences, seasonal pressure changes, and the unequal heating of land and water bodies.
2. Unlike global planetary winds, these systems are temporary or seasonal and cover specific geographic regions.
3. Common examples include tropical and temperate cyclones, anticyclones, air masses, frontal weather systems, and the seasonal monsoons.
🌤️ Class 9 Social Science Exam Preparation Notice: This page features curated SEBA Class 9 Social Science (Geography Section) Chapter 2: Atmosphere: Structure, Air Pressure and Wind System Extra Questions, Answers & Solutions updated for the 2026–27 academic session. Tailored strictly to target high-frequency descriptive, analytical, and diagram-based questions tested in school unit evaluations, half-yearly exams, and annual examinations, this revision guide explores beyond standard textbook exercises—providing structured, point-wise evaluations of atmospheric layering, vertical temperature gradients, global pressure belts, planetary and periodic wind systems, Coriolis deflection, and cyclonic circulation patterns—to guarantee full marks in your 2-mark, 3-mark, and 5-mark exam questions.
💡 Master SEBA Class 9 Geography Chapter Extra Questions:
- Having difficulty structuring a comprehensive 5-mark answer explaining how the planetary wind belts correspond with global high and low pressure cells, detailing the working principles of Ferrel’s Law and the Coriolis Effect, or comparing the weather conditions of tropical cyclones versus anticyclones? Leave your query in the comments section below!
- Bookmark this page for quick revision of thermal lapse rates, wind classification tables (permanent, periodic, local), and isobaric pressure gradient diagrams before your upcoming unit evaluations, half-yearly exams, and final annual examinations.
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