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

Rajasthan BoardEnglish MediumSTD 11 SciencePhysics14. waves and sound1 Mark
MCQ
A source producing sound of frequency $170 Hz$ is approaching a stationary observer with a velocity $17 \,ms^{-1}$. The apparent change in the wavelength of sound heard by the observer is (speed of sound in air $= 340 \,ms^{-1}$)  ..... $m$
  • ✓
    $0.1$
  • B
    $0.2$
  • C
    $0.4$
  • D
    $0.5$
✓

Answer

Correct option: A.
$0.1$
a
(a) $\lambda = \frac{v}{n} = \frac{{340}}{{170}} = 2m,\,\,\,n' = \frac{{340}}{{340 - 17}} \times 170 \Rightarrow n' = 178.9Hz$
Now $\lambda ' = \frac{v}{{n'}} = \frac{{340}}{{178.9}} = 1.9$
==> $\lambda - \lambda ' = 2 - 1.9 = 0.1$

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