UPSC Prelims 2011 · GS Paper I
Question 95: Geography
The jet aircrafts fly very easily and smoothly in the lower stratosphere. What could be the appropriate explanation ?
- 1.There are no clouds or water vapour in the lower stratosphere
- 2.There are no vertical winds in the lower stratosphere.
Which of the statements given above is/are correct in this context ?
AnswerThe answer is (c).
The lower stratosphere, just above the troposphere, is a stable layer because temperature stays roughly constant or rises with height, which suppresses vertical air movement. It has almost no water vapour, so there are no clouds, and little weather or turbulence. The winds there are mostly horizontal. This calm, clear air lets jet aircraft fly smoothly and efficiently.
- 1. There is almost no water vapour or cloud in the lower stratosphere.
- 2. The layer is stable and vertical air movement is minimal.
How you could have got this
- If you were sure statement 1 is correct, (b) and (d) go: each of them leaves 1 out.
What you needed to know: There is almost no water vapour or cloud in the lower stratosphere.
- Then, if you were sure statement 2 is correct, (a) goes: it leaves 2 out.
What you needed to know: The layer is stable and vertical air movement is minimal.
Only (c) is left. This one needs every statement.
This follows an unofficial answer: UPSC has not published its key for this year, and if that answer is wrong, so is this path.
Which options go is worked out from UPSC’s key and the options, not by a model.
Why each option is right or wrong
- (a) No clouds is correct, but absence of vertical winds is also correct.
- (b) No vertical winds is correct, but absence of clouds is also correct.
- (c) Right: no clouds or water vapour, and no vertical winds, give smooth flight.
- (d) Both statements are correct, so 'neither' fails.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2011, General Studies Paper I, Series A. The paper on upsc.gov.in.