NEET Sample Paper NEET Sample Test Paper-34

  • question_answer
    A fixed source of souna emitting a certain frequency appears at \[{{f}_{a}}\] when the observer is approaching the source with speed \[{{v}_{0}}\] and frequency\[{{f}_{r}}\]. when the observer recedes from the source with the same speed. The frequency of the source is :-

    A)  \[\frac{{{f}_{a}}+{{f}_{r}}}{2}\]

    B)  \[\frac{{{f}_{a}}-{{f}_{r}}}{2}\]

    C)  \[\sqrt{{{f}_{a}}{{f}_{r}}}\]

    D)  \[\frac{2{{f}_{r}}{{f}_{a}}}{{{f}_{r}}+{{f}_{a}}}\]

    Correct Answer: A

    Solution :

    \[{{f}_{a}}=\left[ \frac{v+{{v}_{0}}}{v} \right]f\]  ?.(1)  \[{{f}_{r}}=\left[ \frac{v-{{v}_{0}}}{v} \right]f\] ?.(2) \[\frac{{{f}_{a}}}{f}=1+\frac{{{v}_{0}}}{v}\] and \[\frac{{{f}_{r}}}{f}=1-\frac{{{v}_{0}}}{v}\] then \[\frac{{{f}_{a}}}{f}+\frac{{{f}_{r}}}{f}=2\Rightarrow f=\frac{{{f}_{a}}+{{f}_{r}}}{2}\]

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