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Standard XII

Physics

Finding Average Velocity

A source prod...

Question

A source producing sound of frequency 170Hz is approaching a stationary observer with a velocity 17m/s. The apparent change in the wave length of sound heard by the observer is:
(speed of the sound in air = 340m/s)

0.1 m

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0.2 m

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0.4 m

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0.5 m

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Solution

The correct option is A 0.1 m
Wavelength of sound $= \frac{v}{f} = \frac{340}{170} = 2 m$
Apparent frequency, $f^{'} = (\frac{v}{v - v_{s}}) f$
$f \propto \frac{1}{λ}$
$\Rightarrow λ^{1} = (\frac{v - v_{s}}{v}) λ$ $= \frac{19}{20} \times 2 m = 1.9 m$
$∴$ Apparent change $= 0.1 m$

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A source producing sound of frequency 170Hz is approaching a stationary observer with a velocity 17m/s. The apparent change in the wave length of sound heard by the observer is: (speed of the sound in air = 340m/s)

The correct option is A 0.1 mWavelength of sound =vf=340170=2 mApparent frequency, f′=(vv−vs)ff∝1λ⇒λ1=(v−vsv)λ =1920×2 m=1.9 m∴ Apparent change =0.1 m

A source producing sound of frequency 170Hz is approaching a stationary observer with a velocity 17m/s. The apparent change in the wave length of sound heard by the observer is:
(speed of the sound in air = 340m/s)

The correct option is A 0.1 m
Wavelength of sound $= \frac{v}{f} = \frac{340}{170} = 2 m$
Apparent frequency, $f^{'} = (\frac{v}{v - v_{s}}) f$
$f \propto \frac{1}{λ}$
$\Rightarrow λ^{1} = (\frac{v - v_{s}}{v}) λ$ $= \frac{19}{20} \times 2 m = 1.9 m$
$∴$ Apparent change $= 0.1 m$