Q84 / 160 · JIPMER 2014 · Physics

A sound source producing waves of frequency 300 Hz and wavelength 1 m observer is stationary, while source is going away with the velocity $30 \mathrm{~m} / \mathrm{s}$, then apparent frequency heared by the observer is

  • A
    $270\mathrm{~Hz}$
  • Correct answer
    B
    $273\mathrm{~Hz}$
  • C
    $383\mathrm{~Hz}$
  • D
    $300\mathrm{~Hz}$

Solution

Apparent frequency $n^{\prime}=n\left(\frac{v}{v+v_s}\right)$ $\begin{aligned} v & =\text { velocity of sound, } \\ v_s & =\text { velocity of source }\end{aligned}$ $\therefore \quad n^{\prime}=300\left(\frac{332}{332+30}\right)=273 \mathrm{~Hz}$

Hence, the correct answer is option: 'B'.

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