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JCECE Medical JCECE Medical Solved Paper-2003

  • question_answer
    A source and an observer move away from each other, with a velocity of 20 m/s. If the apparent frequency heard by the observer is 1840 Hz, the actual frequency of the source is: (Velocity of sound in air = 340 m/s):

    A)  2486 Hz      

    B)  2070 Hz

    C)  2134 Hz      

    D)  1872 Hz

    Correct Answer: B

    Solution :

     Key Idea: Movement of the source and observer alters the wavelength and the perceived frequency of sound. As both source and observer are moving away, so observed frequency decreases. \[\therefore \] \[f=\left( \frac{v-{{v}_{0}}}{v+{{v}_{s}}} \right)f\] where\[v\]is the velocity of sound\[~=340\text{ }m/s\] Here,\[{{v}_{0}}=20\,m/s,\,{{v}_{s}}=20\,m/s,f=1840\,Hz\] \[\therefore \] \[1840=\left( \frac{340-20}{340+30} \right)f\] or \[f=\frac{1840\times 360}{320}=2070\,Hz\]


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