Physics Waves ETEA 2015
PMDC Verified Question 114 of 125
The ratio between the velocity of sound in air at 4 atm and that at 3 atm pressure would be:
A
1 : 1
B
4 : 1
C
1 : 4
D
3 : 1
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: 1 : 1
Concept:

The speed of sound in an ideal gas is given by Laplace's formula: \( v = \sqrt{\frac{\gamma P}{\rho}} \).

Solution:

  • According to Boyle's Law, at a constant temperature, density (\( \rho \)) is directly proportional to pressure (\( P \)).


  • If pressure increases from 3 atm to 4 atm, the density of the air increases by the exact same proportion.


  • Therefore, the ratio \( \frac{P}{\rho} \) remains perfectly constant. The speed of sound is independent of pressure changes.


  • The velocity remains the same, giving a ratio of 1:1.


Why other options are incorrect:

Students often wrongly assume speed scales linearly with pressure without considering the simultaneous density increase.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

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