• question_answer
                    A vehicle, with a horn of frequency n is moving with a velocity of 30 m/s in a direction perpendicular to the straight line joining the observer and the vehicle. The observer perceives the sound to have a frequency \[n+{{n}_{1}}\]. Then: (if the sound velocity in air is 300 m/s)                                      

    A)                 \[{{n}_{1}}=10\,n\]

    B)                 \[{{n}_{1}}=0\] 

    C)                 \[{{n}_{1}}=0.1\,n\]       

    D)                 \[{{n}_{1}}=-0.1\,n\]

    Correct Answer: B

    Solution :

                    When velocity of source (vehicle) is perpendicular to the line joining the observer and source, then there is no Doppler's effect of sound or, there is no change in apparent frequency. Therefore, \[{{n}_{1}}=0\].

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