Two sources of sound placed close to each other, are emitting progressive waves given by y1 = 4sin600 π t and y2 = 5sin608 π t An observer located near these two sources of sound will hear (a) 4 beats per second with intensity ratio 25: 16 between waxing and waning. (b) 8 beats per second with intensity ratio 25: 16 between waxing and waning. (c) 8 beats per second with intensity ratio 81: 1 between waxing and waning. (d) 4 beats per second with intensity ratio 81: 1 between waxing and waning.

Answer: (d). f₁ = (600π)/(2π) = 300 Hz, f₂ = (608π)/(2π) = 304 Hz, so 4 beats/s ImaxImin = ((5+4)²)/((5-4)²) = 81: 1 So the answer is (d) 4 beats per second with intensity ratio 81: 1.

Two sources of sound placed close to each other, are emitting… | NEET 2012 (AIPMT, Prelims)

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Beats

Two sources of sound placed close to each other, are emitting progressive waves given by y1 = 4sin600 $\pi$ t and y2 = 5sin608 $\pi$ t

An observer located near these two sources of sound will hear

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Answer: (d)

$f_1 = \frac{600\pi}{2\pi} = 300\text{ Hz}$ , $f_2 = \frac{608\pi}{2\pi} = 304\text{ Hz}$ , so 4 beats/s
$\frac{I_{max}}{I_{min}} = \frac{(5+4)^2}{(5-4)^2} = 81 : 1$
So the answer is (d) 4 beats per second with intensity ratio 81 : 1.

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