UPSC Prelims 2007 Q107: Science & Technology – Physics
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?
- (a) 1 only
- (b) 2 only
- (c) Both 1 and 2
- (d) Neither 1 nor 2
Answer: (d) Neither 1 nor 2
Explanation
Flute pitch and sound in rocks
| Statement | Physics | Verdict |
|---|---|---|
| 1. A shorter flute gives lower frequency | A flute is an air column. Shorter air column → shorter wavelength → HIGHER frequency | FALSE |
| 2. Sound travels in rocks only as longitudinal waves | Solids can carry both longitudinal (P) and transverse (S) waves — seen in earthquake seismic waves | FALSE |
Seismic body waves:
| Wave | Type | Travels through |
|---|---|---|
| P-wave | Longitudinal | Solids, liquids, gases |
| S-wave | Transverse | Solids only |
S-waves cannot pass the liquid outer core — this is how we know the outer core is liquid.
Answer: (d) Neither 1 nor 2.
Why each option is right or wrong
- (a) Incorrect. A shorter flute gives a higher, not lower, frequency.
- (b) Incorrect. Rocks carry transverse waves too (S-waves), so 'longitudinal only' is wrong.
- (c) Incorrect. Both statements are false.
- (d) CORRECT. Shorter flute → higher pitch; rocks carry both P and S waves.
Key point
Shorter air column → higher frequency. Solids carry both longitudinal (P) and transverse (S) waves; liquids/gases only longitudinal.
Remember
Shorter flute = higher pitch; rocks carry both P and S waves.
Common mistakes
- Thinking smaller instruments give deeper sound — the opposite is true (piccolo vs bass flute).
- Applying the 'sound is longitudinal' rule from air to solids.
- Forgetting the link to seismic S-waves and the liquid outer core.
Exam tip
Strong word 'only' → check for exceptions. Solids allow shear, so transverse waves exist.
Sources
- NCERT Class IX — Science, Ch 12 (Sound)
- NCERT Class XI — Physics Part II, Ch 15 (Waves)
- NCERT Class XI — Fundamentals of Physical Geography, Ch 3 (Interior of the Earth)