An observer moves towards a stationary source of sound, with velocity one-fifth of the velocity of sound.…
An observer moves towards a stationary source of sound, with velocity one-fifth of the velocity of sound. What is the percentage increase in the apparent frequency?
$5\%$
$20\%$
zero
$0.5\%$
Solution
When observer moves towards stationary source, then apparent frequency,
$f' = \left[\frac{v + v_o}{v}\right] f = \left[\frac{v + v/5}{v}\right] f = \frac{6}{5} f = 1.2f$
Increment in frequency $= 0.2 f$, so percentage change in frequency $= \frac{0.2f}{f} \times 100 = 20\%$