2001 General Studies, all questions

UPSC Prelims 2001 · General Studies

Question 101: Science and Technology

Assertion (A): A stick is dipped in water in a slanting position. If observed sideways, the stick appears short and bent at the surface of water. Reason (R): The light coming from the stick undergoes scattering from water molecules giving the stick a short and bent appearance.

aBoth A and R are individually true and R is the correct explanation of A
bBoth A and R are individually true but R is NOT a correct explanation of A
cA is true but R is false
dA is false but R is true

AnswerThe answer is (c).

A is true: a stick dipped in water looks bent and shorter because of refraction, since light from the submerged part bends away from the normal as it leaves the water. R is false: the effect is not due to scattering by water molecules but to the change in the speed of light between water and air. Remember that apparent depth and bending are refraction effects, while the blue colour of the sky is scattering.

  • A. A partly dipped stick appears bent and shortened.
  • R. The cause is refraction, not scattering.

How you could have got this

If you were sure statement 1 is correct, (d) goes. Then judge the second statement; if it is correct too, decide whether it explains the first.

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) R is false, so it cannot explain A.
  • (b) R is false, not merely a non-explanation.
  • (c) Right: A is true, R is false.
  • (d) A is true, not false.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2001, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.