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  • 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

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.

Answers (1)

When the observer is at rest and the source of sound is moving towards the observer, then the observed frequency is given by 

n'=\left (\frac{v}{v-v_{s}} \right )n_{0}

where n0 is the original frequency of the source of sound 

and, v is the speed of sound in the medium

n'>n_{0}

When the source is moving away from the observer

n" = \frac{vn_{0}}{v+v_{s}}   (vs=speed of source )

n^{''}< n_{0}

Thus, n’ > n” and graph (c) is correct.

Posted by

infoexpert24

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