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JEE Main & Advanced Physics Wave Mechanics Question Bank Self Evaluation Test - Waves

  • question_answer
    Two factories are sounding their sirens at 800 Hz. A man goes from one factory to other at a speed of 2m/s. The velocity of sound is 320 m/s. The number of beats heard by the person in one second will be:

    A)  2

    B)  4     

    C) 8

    D) 10

    Correct Answer: D

    Solution :

    [d] Frequency of sound produced by siren, \[f=800Hz\] Speed of observer, u = 2 m/s Velocity of sound, v = 320 m/s No. of beats heard per second =? No. of extra waves received by the observer per second \[=\pm \,\,4\lambda \] \[\therefore \] No. of beats/ sec \[=\frac{2}{\lambda }-\left( -\frac{2}{\lambda } \right)=\frac{4}{\lambda }\] \[=\frac{2\times 2}{\frac{320}{800}}=\frac{2\times 2\times 800}{320}=10\]            \[\left( \therefore \lambda =\frac{V}{f} \right)\]


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