UPSC Prelims 2007 · General Studies
Question 107: Science and Technology
Consider the following statements:
- 1.A flute of smaller length gives waves of lower frequency.
- 2.Sound travels in rocks in the form of longitudinal elastic waves only.
Which of the statements given above is/are correct?
AnswerThe answer is (d).
A shorter flute has a shorter air column, which vibrates faster, so it gives higher, not lower, frequency: frequency varies inversely with length. Sound in rock travels both as longitudinal waves (P-waves) and as transverse waves (S-waves), as seismology shows, so 'longitudinal only' is wrong. Both statements are false.
- 1. A shorter flute gives higher frequency.
- 2. Rocks carry transverse (S) waves as well as longitudinal waves.
How you could have got this
- If you were sure statement 2 is not correct, (b) and (c) go: each of them includes 2.
What you needed to know: Rocks carry transverse (S) waves as well as longitudinal waves.
The red flag in statement 2 is “only”. In UPSC’s papers, statements with “only” were true 27% of the time (82 statements). A hint, not a rule.
- Then, if you were sure statement 1 is not correct, (a) goes: it includes 1.
What you needed to know: A shorter flute gives higher frequency.
Only (d) 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 wrong; shorter means higher frequency.
- (b) Statement 2 is wrong; rocks also carry transverse waves.
- (c) Both statements are wrong.
- (d) Correct: neither statement holds.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2007, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.