wave_mechanics dopplers_effect Question 9
Question: A whistle sends out 256 waves in a second. If the whistle approaches the observer with velocity 1/3 of the velocity of sound in air, the number of waves per second the observer will receive
[MP PET 1990; DPMT 2002]
Options:
A) 384
B) 192
C) 300
D) 200
Show Answer
Answer:
Correct Answer: A
Solution:
Wave number = $ \frac{1}{\lambda } $ but $ \frac{1}{\lambda ‘}=\frac{1}{\lambda }( \frac{v}{v-v _{s}} )\text{and}\ v _{s}=\frac{v}{3} $
$ \therefore $ (W.N.)? = (W.N.) $ ( \frac{v}{v-v/3} )=256\times \frac{v}{2v/3} $ = $ \frac{3}{2}\times 256=384 $
BETA
