First slide

Doppler's effect

Question

A boy is walking away from a wall towards an observer at a speed of 1 metre/sec and blows a whistle whose frequency is 680 Hz. The number of beats heard by the observer per second is (Velocity of sound in air = 340 metres/sec

Difficult

A

Zero
B

2
C

8
D

4

Solution

Observer hears two frequencies
(i) n₁ which is coming from the source directly
(ii) n₂ which is coming from the reflection image of source
so, $n_{1} = 680 (\frac{340}{340 - 1})$ and $n_{2} = 680 (\frac{340}{340 + 1})$
$\Rightarrow n_{1} - n_{2} = 4 beats$

Get Instant Solutions

When in doubt download our app. Now available Google Play Store- Doubts App

Recieve an sms with download link

Doubts App

OR

SCAN ME

Doubts App

Doubts App