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A train whistling at constant frequency ...

A train whistling at constant frequency is moving towards a station at a constant speed V. The train goes past a stationary observer on the station. The frequency `n^(')` of the sound as heard by the observer is plotted as a function of time t, figure. Identify the expected curve.

A

B

C

D

Text Solution

Verified by Experts

The correct Answer is:
C
Let th original frequency of the source is `n_(0)`.
Let the speed of sound wave in the medium is v.
As observer is stationary

Apparent frequecny `n_(a)=((v)/(v-v_(s)))n_(0)" "` [when train is approaching]
`" " =((v)/(v-v_(s)))n_(0)=n_(a)gt n_(0)`
When the train is going away from the observer
Apparent frquency `n_(a)=((v)/(v+v_(s)))n_(0)=n_(a)ltn_(0)`
Hence, the expected curve is (c).
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