Q107 / 125 · BITSAT 2012 · Physics

A sound souorce is moving towards stationary listener with $\frac{1}{10}$ th of the speed of sound. The ratio of apparent to read frequency is

  • A
    $\left(\frac{9}{10}\right)^{2}$
  • Correct answer
    B
    $\left(\frac{10}{9}\right)$
  • C
    $\left(\frac{11}{10}\right)$
  • D
    $\left(\frac{11}{10}\right)^{2}$

Solution

$v_{\mathrm{s}}=\frac{\mathrm{v}}{10} \quad \mathrm{n}^{\prime}=\mathrm{n} \frac{\mathrm{v}}{\mathrm{v}-\mathrm{v}_{\mathrm{s}}}$ $\frac{\mathrm{n}^{\prime}}{\mathrm{n}}=\frac{\mathrm{v}}{\left(\mathrm{v}-\frac{\mathrm{v}}{10}\right)}=\frac{10}{9}$

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

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