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JEE Main & Advanced Physics Wave Mechanics Question Bank Doppler's Effect

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    A source of sound and listener are approaching each other with a speed of 40 m/s. The apparent frequency of note produced by the source is 400 cps. Then, its true frequency (in cps) is (velocity of sound in air = 360 m/s)         [KCET 1999]

    A)            420

    B)            360

    C)            400

    D)            320

    Correct Answer: D

    Solution :

               \[n'=n\,\left( \frac{v+{{v}_{O}}}{v-{{v}_{S}}} \right)\,n\Rightarrow 400=n\,\left( \frac{360+40}{360-40} \right)\Rightarrow n=320\,cps\]


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