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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) 2nv0v

B) nv0v

C) v2nv0

D) vnv0

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(v+v0v)  ..........(i)

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

n=n(vv0v)    .......(ii)

 From Eqs .(i) and (ii) , we get

nn=nv(v+v0v+v0)

 = 2nv0v