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Punjab Medical Punjab - MET Solved Paper-2009

  • question_answer
    Two sources are at a finite distance apart. They emit sound of wavelength\[\lambda \]. An observer situated between them on line joining the sources, approaches towards one source with speed\[u\], then the number of beats heard per second by observer will be

    A) \[\frac{2u}{\lambda }\]                                

    B) \[\frac{u}{\lambda }\]

    C) \[\frac{u}{2\lambda }\]                                

    D) \[\frac{\lambda }{u}\]

    Correct Answer: A

    Solution :

    \[{{n}_{1}}=\left( \frac{v+u}{v} \right)n\]and\[{{n}_{2}}=\left( \frac{v-u}{v} \right)n\] Number of beats per second                 \[x={{n}_{1}}-{{n}_{2}}\]                    \[=\left( \frac{v+u}{v} \right)n-\left( \frac{v-u}{v} \right)n\]                    \[=\left( \frac{v+u-v+u}{v} \right)n\]                    \[=2u\left( \frac{n}{v} \right)=\frac{2u}{v}\]


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