# An observer moves towards a stationary source of sound, with a velocity one­fifth of the velocity of sound. What is the percentage increase in the apparent frequency ? Option 1) 5% Option 2) 20% Option 3) 0 Option 4) 0.5%

As we learnt in

Doppler Effect -

When a source of sound and a listener are in motion relative to each other, the frequency of the sound heard by the listener is not the same as the source frequency.

-

By Doppler's effect

$\frac{{\upsilon }'}{\upsilon }= \frac{\nu _{s}+\nu _{0}}{\nu _{s}}$ (where $v_{s}$ is the velocity of sound)

$\; \; \; \; \; \; \; = \frac{\nu+\left ( \nu /5 \right ) }{\nu }= \frac{6}{5}$

$\therefore \; \; \; \; \; \; \; \; Fractional \: \: increase$

$\; \; \; \; \; \; \; \; \; \; \; \; \; \; \; \frac{{\upsilon }'-\upsilon }{\upsilon }= \left ( \frac{6}{5} -1\right )= \frac{1}{5}$

$\therefore \; \; \; \; \; \; \; \; Percentage\: \: increase\: \: = \frac{100}{5}=$

Correct option is 2.

Option 1)

5%

This is an incorrect option.

Option 2)

20%

This is the correct option.

Option 3)

0

This is an incorrect option.

Option 4)

0.5%

This is an incorrect option.

### Preparation Products

##### JEE Main Rank Booster 2021

This course will help student to be better prepared and study in the right direction for JEE Main..

₹ 13999/- ₹ 9999/-
##### Knockout JEE Main April 2021 (Subscription)

An exhaustive E-learning program for the complete preparation of JEE Main..

₹ 6999/- ₹ 5/-
##### Knockout JEE Main April 2021

An exhaustive E-learning program for the complete preparation of JEE Main..

₹ 22999/- ₹ 14999/-
##### Knockout JEE Main April 2022

An exhaustive E-learning program for the complete preparation of JEE Main..

₹ 34999/- ₹ 24999/-