Question:

Two sources of sound are emitting progressive waves \(\mathrm{y}_1=4 \sin 710 \pi \mathrm{t}\) and \(\mathrm{y}_2=3 \sin 702 \pi \mathrm{t}\). The sources are placed close to each other. The number of beats heard per second and intensity ratio between waxing and waning are respectively

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Beat frequency is the difference of the two frequencies; the intensity ratio uses the sum and difference of the amplitudes squared.
Updated On: Nov 13, 2026
  • \(4,16:9\)
  • \(8,16:9\)
  • \(4,49:1\)
  • \(8,49:1\)
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The Correct Option is C

Solution and Explanation

Step 1: Understanding the Concept
For \(y=A\sin 2\pi ft\), the angular frequency is \(\omega=2\pi f\). Beats per second equal \(f_1-f_2\).

Step 2: Beat frequency
\(f_1=\dfrac{710\pi}{2\pi}=355\text{ Hz}\) and \(f_2=\dfrac{702\pi}{2\pi}=351\text{ Hz}\), so beats per second \(=4\).

Step 3: Intensity ratio
Intensity is proportional to amplitude squared. Maximum amplitude is \(4+3=7\) and minimum is \(4-3=1\).

Step 4: Result
\(\dfrac{I_{max}}{I_{min}}=\dfrac{7^2}{1^2}=49:1\).

Final Answer:
There are 4 beats per second and the intensity ratio is 49:1. \[ \boxed{\text{(C) }4,\ 49:1} \]
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