First slide

Beats

Question

On sounding tuning fork A with another tuning fork B of frequency 384 Hz, 6 beats are produced per second. After loading the prongs of A with some wax and then sounding it again with B, 4 beats are produced per second. What is the frequency of the tuning fork A

Easy

A

388 Hz
B

380 Hz
C

378 Hz
D

390 Hz

Solution

n_A = ?, n_B = 384 Hz
x = 6 bps, which is decreasing (from 6 to 4) i.e. x $↓$
Tuning fork A is loaded so n_A $↓$
Hence n_A $↓$ – n_B = x $↓$ $\to$ Correct
n_B – n_A $↓$ = x $↓$ $\to$ Wrong
$\Rightarrow$ n_A = n_B + x = 384 + 6 = 390 Hz.

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