Question:

Two sources of sound placed close to each other are emitting progressive waves given by
\(y_{1}=4\,\sin (600\pi t)\) and \(y_{2}=5\,\sin (608\pi t)\).
An observer located near these two sources of sound will hear

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Beat frequency is the difference of the two frequencies, and the intensity ratio comes from the maximum and minimum amplitudes.
Updated On: Nov 12, 2026
  • \(4\) beats/s with intensity ratio \(25:16\) between waxing and waning.
  • \(8\) beats/s with intensity ratio \(25:16\) between waxing and waning.
  • \(8\) beats/s with intensity ratio \(81:1\) between waxing and waning.
  • \(4\) beats/s with intensity ratio \(81:1\) between waxing and waning.
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The Correct Option is D

Solution and Explanation

Step 1: Understanding the Concept
For \(y=a\sin(\omega t)\), the frequency is \(f=\frac{\omega}{2\pi}\). Beats occur at the difference of the two frequencies.

Step 2: Calculation
\(f_{1}=\frac{600\pi}{2\pi}=300\ \text{Hz}\) and \(f_{2}=\frac{608\pi}{2\pi}=304\ \text{Hz}\), so the beat frequency is \(4\) beats/s. The maximum amplitude is \(4+5=9\) and the minimum is \(5-4=1\).

Step 3: Compare the options
Intensity is proportional to amplitude squared, so \(\frac{I_{max}}{I_{min}}=\frac{81}{1}\). So the answer is 4 beats/s with ratio \(81:1\).

Final Answer:
The observer hears 4 beats/s with an intensity ratio of \(81:1\). \[ \boxed{\text{(D) }\text{4 beats/s with intensity ratio 81:1 between waxing and waning}} \]
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