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Discussion Forum



1)

The observer is moving with velocity 'v0' towards the stationary source of sound and then after crossing moves away from the source with velocity 'v0' . Assume that the medium through which the sound waves travel is at rest.If v is the velocity of sound and n is the frequency emitted by the source, then the difference  between apparent frequencies heard by the observer is 


A) $\frac{2nv_{0}}{v}$

B) $\frac{nv_{0}}{v}$

C) $\frac{v}{2nv_{0}}$

D) $\frac{v}{nv_{0}}$

Answer:

Option A

Explanation:

When the observer is moving towards the source and source is stationary , then the apparent  frequency is given as,

   $n'=n\left(\frac{v+v_{0}}{v}\right)$  ..........(i)

When the observer is moving away from the source and the source is stationary , then the apparent frequency is given as,

$n''=-n\left(\frac{v-v_{0}}{v}\right)$    .......(ii)

 From Eqs .(i) and (ii) , we get

$n'- n''=\frac{n}{v}(v'+v_{0}-v+v_{0})$

 = $\frac {2nv_{0}}{v}$