UPSC Prelims 2004 Q71: Geography – Atmosphere & Climatology
- (a) Both A and R are individually true and R is the correct explanation of A
- (b) Both A and R are individually true but R is not the correct explanation of A
- (c) A is true but R is false
- (d) A is false but R is true
Answer: (a) Both A and R are individually true and R is the correct explanation of A
Explanation
> Note for students: Some answer keys give (d) A is false but R is true, but the atmosphere is in fact thickest over the Equator, so the correct answer by facts is (a). If your source key differs, trust the facts.
Thickness of the atmosphere over the Equator
| Part | Verdict |
|---|---|
| A. Atmosphere is thickest over the Equator | True — about 16 to 18 km thick, against 8 km at the poles |
| R. High insolation and strong convection currents over the Equator | True — and they explain the greater height |
Both are true and R explains A: strong heating and convection lift the air higher over the Equator, so the troposphere is thickest there. (The circulated key said A is false; the real answer is (a).)
Answer: (a) Both A and R are true and R explains A.
Why each option is right or wrong
- (a) CORRECT. A is true and R gives the reason, the high insolation and convection.
- (b) Incorrect. R does explain A, so this code is wrong.
- (c) Incorrect. R is true, so this code is wrong.
- (d) Incorrect. A is true, so this code is wrong.
Key point
Troposphere: about 18 km at the Equator, 8 km at the poles.
Remember
The atmosphere is thickest over the Equator because of convection.
Common mistakes
- Thinking the atmosphere is thicker at the poles.
- Not linking convection with the height of the troposphere.
- Trusting a circulated key without testing the statement.
Exam tip
Equatorial troposphere is the thickest due to strong convection.
Sources
- NCERT Class XI Geography — Composition and Structure of Atmosphere
- Savindra Singh — Climatology (Prayag Pustak Bhawan)