UPSC Prelims 2005 · General Studies

Question 17: Science and Technology

Consider the following statements :

1.A geostationary satellite is at an approximate height of 10,000 km
2.FM transmission of music is of very good quality because the atmospheric or man-made noises which are generally frequency variations can do little harm.

Which of the statements given above is/are correct?

a1 only

b2 only

cBoth 1 and 2

dNeither 1 nor 2

AnswerThe answer is (b).

Statement 1 is wrong: a geostationary satellite orbits about 36,000 km above the equator, not 10,000 km. Statement 2 is the intended point: FM carries the music in changes of frequency, and the receiver strips off amplitude changes, which is how static and man-made noise mostly arrive, so the sound stays clean. Strictly, the noise is amplitude variation, so the statement's wording is loose.

1. A geostationary satellite is at about 36,000 km.
2. FM resists noise because receivers ignore amplitude changes (see doubt on the wording).

How you could have got this

If you were sure statement 1 is not correct, (a) and (c) go: each of them includes 1.
What you needed to know: A geostationary satellite is at about 36,000 km.
Then, if you were sure statement 2 is correct, (d) goes: it leaves 2 out.
What you needed to know: FM resists noise because receivers ignore amplitude changes (see doubt on the wording).

Only (b) 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) Statement 1 is false: a geostationary orbit is about 36,000 km up.
(b) Correct per the key: statement 1 false, statement 2 accepted.
(c) Includes statement 1, which is false.
(d) Rejects statement 2, but the key accepts it as the standard FM noise-immunity point.

Worth knowing: Noise mostly shows up as amplitude variation, not frequency variation, so a strict reading of statement 2 makes it false and gives (d); the key accepts the statement as FM's noise-immunity point.

Explanation: written by UPSC Grade, not by UPSC.

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Source: UPSC, Civil Services (Preliminary) Examination 2005, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.