Waves - Result Question 54
56. Two sources $P$ and $Q$ produce notes of frequency $660 Hz$ each. A listener moves from $P$ to $Q$ with a speed of $1 ms^{-1}$. If the speed of sound is $330 m / s$, then the number of beats heard by the listener per second will be
[NEET Kar. 2013]
(a) zero
(b) 4
(c) 8
(d) 2
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Answer:
Correct Answer: 56. (b)
Solution:
(b) $\frac{\Delta f}{f}=\frac{v}{c}$
$\Rightarrow \frac{(\text{ Beats }) / 2}{f}=\frac{v}{c}$
$\Rightarrow$ Beats $=\frac{2 f v}{c}=4$
