1997 General Studies, all questions
UPSC Prelims 1997 · General Studies
Question 13: Science and Technology
The tail of a comet is directed away from the sun because
aas the comet rotates around the sun, the lighter mass of the comet is pushed away due to the centrifugal force alone
bas the comet rotates, the lighter mass of the comet is attracted by some star situated in the direction of its tail
cthe radiation emitted by the sun exerts a radial pressure on the comet throwing its tail away from the sun
dthe tail of the comet always exists in the same orientation
AnswerThe answer is (c).
A comet's tail points away from the Sun because sunlight exerts radiation pressure on the gas and dust released from the comet, and the solar wind sweeps this material outward. So the tail streams away from the Sun, trailing the comet on its way in and leading it on its way out. Remember: the tail is pushed, not pulled, and it has nothing to do with the comet's rotation.
Why each option is right or wrong
- (a) Centrifugal force from orbiting the Sun does not blow the tail away; the Sun's radiation and wind do.
- (b) No star lies in the direction of the tail to attract it.
- (c) Right: radiation pressure from the Sun pushes the tail away.
- (d) The tail's direction changes as the comet moves relative to the Sun, so it is not fixed.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 1997, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.