UPSC Prelims 2012 · GS Paper I
Question 45: Geography
Consider the following factors :
- 1.Rotation of the Earth
- 2.Air pressure and wind
- 3.Density of ocean water
- 4.Revolution of the Earth
Which of the above factors influence the ocean currents?
AnswerUPSC’s answer is (b).
Ocean currents arise from the Earth's rotation (the Coriolis effect, which deflects flow), from planetary winds and air pressure differences that push surface water, and from differences in water density caused by temperature and salinity, which drive vertical and deep currents. The Earth's revolution around the Sun, which causes seasons, is not a factor.
- 1. Earth's rotation deflects currents through the Coriolis effect.
- 2. Winds and air pressure differences drive surface currents.
- 3. Temperature and salinity differences change density and drive deep currents.
- 4. Revolution around the Sun causes seasons, not ocean currents.
How you could have got this
- If you were sure statement 1 is correct, (d) goes: it leaves 1 out.
What you needed to know: Earth's rotation deflects currents through the Coriolis effect.
- Then, if you were sure statement 3 is correct, (a) and (c) go: each of them leaves 3 out.
What you needed to know: Temperature and salinity differences change density and drive deep currents.
Only (b) is left. You didn’t need statements 2 or 4.
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) Incomplete: density of ocean water also influences currents.
- (b) Correct: rotation, air pressure and wind, and density.
- (c) Wrong: revolution does not influence currents, and it leaves out wind and density.
- (d) Wrong: it includes the Earth's revolution and omits rotation.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2012, General Studies Paper I, Series A. The paper on upsc.gov.in.