Question

A source of sound moves towards a stationary listener with the velocity of sound. If the actual frequency of the sound produced by the source be $f,$ then change in frequency will be

• A. $f$
• B. $\frac{f}{2}$
• C. $\frac{f}{4}$
• D. none of these

Answer 1

Answer: (D)

Step 1: Given that:

Speed of source of sound($v_s$)= Velocity of sound($v$)

The actual frequency of the sound produced by the source of sound= $f$

Step 2: Calculation of change in frequency of sound:

When a source of sound of frequency $f$ approaches a stationary listener with velocity $v_s$ then the change in frequency experienced by the listener is;

$\Delta f=f\left(\frac{v_s}{v-v_s}\right)$

Where,

$v=speedofsoundinair$

$v_s=speedofsourceofsound$

Thus,

According to the question, $v_s=v$ , we get;

$\Delta f=f\left(\frac{v}{v-v}\right)$

$\Delta f=f\times \left(\frac{v}{0}\right)$

$\Delta f=\infty$

Thus,

The change in frequency will be infinite.

Hence,

Option D) none of these is the correct option.