Question

An observer is moving away from a stationary source of sound emitting a note of frequency $n$. The velocity of the observer is 0.1% more than the speed of the sound. Then, the apparent frequency is

• A. $n$
• B. $n/100$
• C. $-n/100$
• D. Doppler effect does not occur

Answer 1

Answer: (D)

Doppler effect does not occur

Velocity of an observer $\left(v_o\right)$which is moving away from the source is greater than velocity of sound $v_s$.

$v_o=1.001v_s$

If we apply Doppler effect in case when observer moves away from stationary source :

Apparent frequency ${\nu }^{\prime }=n[\frac{v_{sound}-v_o}{v_{sound}}]$

${\nu }^{\prime }=n[\frac{v_s-1.001v_s}{v_s}]⟹{\nu }^{\prime }<0$ which is not possible.

Thus Doppler effect does not occur.