Wave Mechanics Question 668
Question: Two factories are sounding their sirens at 800 Hz. A man goes from one factory to other at a speed of 2m/s. The velocity of sound is 320 m/s. The number of beats heard by the person in one second will be:
Options:
A) 2
B) 4
C) 8
D) 10
Show Answer
Answer:
Correct Answer: D
Solution:
[d] Frequency of sound produced by siren, $ f=800Hz $ Speed of observer, u = 2 m/s Velocity of sound, v = 320 m/s No. of beats heard per second =? No. of extra waves received by the observer per second $ =\pm 4\lambda $
$ \
Therefore $ No. of beats/ sec $ =\frac{2}{\lambda }-( -\frac{2}{\lambda } )=\frac{4}{\lambda } $
$ =\frac{2\times 2}{\frac{320}{800}}=\frac{2\times 2\times 800}{320}=10 $
$ ( \
Therefore \lambda =\frac{V}{f} ) $
BETA
