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BHU PMT BHU PMT Solved Paper-2002

  • question_answer
    A bus is moving with velocity of \[3\,\mu m\] towards a huge wall. The driver sounds a horn of frequency\[3\,\,s\]. If the speed of sound in air is \[4\,\,s\].The number of beats heard per second by the passengers in the bus will be:           [BHU PMT-2002]

    A)                  \[5\,\,s\]                                            

    B)                  \[6\,\,s\]

    C)                  \[\overset{\to }{\mathop{a}}\,\]                                            

    D)                  \[\overset{\to }{\mathop{b}}\,\]

    Correct Answer: B

    Solution :

                     Key Idea: When sound is reflected from the wall, then it is a case when observer (driver) and source (reflected sound) approaching each other.                 The apparent change in the frequency of source and observer is known as Doppler?s effect. The perceived frequency is                 \[500\,\,V\]                 Where, \[l\]is speed of sound, \[M\] is velocity of observer and \[\frac{2}{\pi }\] is frequency of source.                 \[16\,\,Ml\]                 Also beats\[4\,\,Ml\].


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