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

  • question_answer
    An observer moves towards a stationary source of sound, with a velocity one-fifth of the velocity of sound. What is the percentage increase in the apparent frequency  [AIEEE 2005]

    A)            5% 

    B)            20%

    C)            Zero                                         

    D)            0.5%

    Correct Answer: B

    Solution :

               When observer moves towards stationary source then apparent frequency                    \[n'=\left[ \frac{v+{{v}_{O}}}{v} \right]\,n\]\[=\left[ \frac{v+v/5}{v} \right]\,n\]\[=\frac{6}{5}n=1.2n\] Increment in frequency = 0.2 n so percentage change in frequency = \[\frac{0.2n}{n}\times 100\]= 20%.


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