wave_mechanics dopplers_effect Question 34
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
[MP PMT 1995]
Options:
A) Zero
B) 2
C) 8
D) 4
Show Answer
Answer:
Correct Answer: D
Solution:
Observer hears two frequencies (i) $ n _{1} $ which is coming from the source directly (ii) $ n _{2} $ 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 $
BETA
