Question

When an observer is approaching a stationary source with a velocity $v_0$ then the apparent change in frequency observed by him will be

• A. $\frac{v}{v+v_0}n$
• B. $\frac{v}{v_0}n$
• C. $\frac{v+v_0}{v}n$
• D. $\frac{v_0}{v}n$

Answer 1

Answer: (D)

$\frac{v_0}{v}n$

Given: velocity of sound is $v$ and original frequency is $n$

Using Doppler effect equation when observer is approaching towards stationary source:

$n^{\prime }=n[\frac{v_{sound}+v_{observer}}{v_{sound}}]$ $=n[\frac{v+v_o}{v}]$

$\Delta n=n^{\prime }-n=n[\frac{v+v_o}{v}]-n$

$⟹\Delta n=\frac{n{v}_o}{v}$