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14. waves and sound — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics14. waves and sound1 Mark
MCQ
A source and an observer are moving towards each other with a speed equal to $\frac{v}{2}$ where $v$ is the speed of sound. The source is emitting sound of frequency $n$. The frequency heard by the observer will be
  • A
    Zero
  • B
    $n$
  • C
    $\frac{n}{3}$
  • ✓
    $3n$
✓

Answer

Correct option: D.
$3n$
d
(d)$n' = n\left( {\frac{{v + {v_0}}}{{v - {v_s}}}} \right) = n\,\left( {\frac{{v + v/2}}{{v - v/2}}} \right) = 3n$

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