Question:

The beats are produced by two sound sources of same amplitude and of nearly equal frequencies. The maximum intensity of beats will be {

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Intensity is proportional to the square of amplitude. If amplitude doubles, intensity becomes four times.
  • Same
  • Double
  • Four times
  • Eight times
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The Correct Option is C

Solution and Explanation

When two sound waves of same amplitude are superposed, beats are produced. Let the amplitude of each wave be: \[ a. \] At maximum intensity, the two waves interfere constructively. So, resultant amplitude becomes: \[ A=a+a=2a. \] Now, intensity is proportional to the square of amplitude: \[ I\propto A^2. \] Intensity due to one source is: \[ I_1\propto a^2. \] Maximum intensity due to two sources is: \[ I_{\max}\propto (2a)^2. \] \[ I_{\max}\propto 4a^2. \] Therefore: \[ \frac{I_{\max}}{I_1}=\frac{4a^2}{a^2}. \] \[ \frac{I_{\max}}{I_1}=4. \] Hence, maximum intensity is four times that of one source.
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