(C) The apparent frequency $f_{app}$ is given as $f_{app} = f + 0.1f = 1.1f$. According to the Doppler effect formula: $f_{app} = f \left[ \frac{v + v

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(C) The apparent frequency $f_{app}$ is given as $f_{app} = f + 0.1f = 1.1f$. According to the Doppler effect formula: $f_{app} = f \left[ \frac{v + v_o}{v - v_s} \right]$. Thus,$1.1 = \frac{v + v_o}{v - v_s}$. Case $1$: If the observer is stationary $(v_o = 0)$,then $1.1 = \frac{v}{v - v_s}$. $1.1(v - v_s) = v \Rightarrow 1.1v - 1.1v_s = v \Rightarrow 0.1v = 1.1v_s$. $v_s = \frac{0.1 \times 330}{1.1} = 30 \, m/s$. This matches statement $(i)$. Case $2$: If the source is stationary $(v_s = 0)$,then $1.1 = \frac{v + v_o}{v}$. $1.1v = v + v_o \Rightarrow v_o = 0.1v$. $v_o = 0.1 \times 330 = 33 \, m/s$. This matches statement $(iv)$. Therefore,the correct statements are $(i)$ and $(iv)$.

Class 11 Physics Waves and Sound Doppler’s Effect

Difficult

The apparent frequency of a sound wave as heard by an observer is $10\%$ more than the actual frequency. If the velocity of sound in air is $330 \, m/s$,then
$(i)$ The source may be moving towards the observer with a velocity of $30 \, m/s$
$(ii)$ The source may be moving towards the observer with a velocity of $33 \, m/s$
$(iii)$ The observer may be moving towards the source with a velocity of $30 \, m/s$
$(iv)$ The observer may be moving towards the source with a velocity of $33 \, m/s$

A
$ii, iv$
B
$ii, iii$
C
$i, iv$
D
$iii, iv$

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Class 11

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Waves and Sound

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Doppler’s Effect

Two trains,one coming towards and another going away from an observer,both at $4 \; m/s$,produce a whistle simultaneously of frequency $300 \; Hz$. Find the number of beats produced. (Assume the speed of sound $v = 332 \; m/s$)

Medium

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The wavelength is $120 \, cm$ when the source is stationary. If the source is moving with a relative velocity of $60 \, m/s$ towards the observer,then the wavelength of the sound wave reaching the observer will be ... $cm$ (velocity of sound $= 330 \, m/s$).

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Consider the Doppler effect in two cases. In the first case,an observer moves towards a stationary source of sound with a speed of $50 \,m/s$. In the second case,the observer is at rest and the source moves towards the observer with the same speed of $50 \,m/s$. Then the frequency heard by the observer will be [velocity of sound in air $= 330 \,m/s$.]

EasyMHT CET 2023

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The frequency of sound heard by an observer moving towards a stationary source with certain speed is $n_1$ and if the observer moves away from the same source with same speed,the frequency of sound heard by the observer is $n_2$. If the speed of sound in air is $340 \ m/s$ and $n_1: n_2 = 71: 65$,then the speed of the observer is: (in $km/h$)

MediumTS EAMCET 2025

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$A$ source of sound $S$ of frequency $500 \ Hz$ situated between a stationary observer $O$ and a wall $W$,moves towards the wall with a speed of $2 \ m/s$. If the velocity of sound is $332 \ m/s$,then the number of beats per second heard by the observer is (approximately)

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Two trains,one coming towards and another going away from an observer,both at $4 \; m/s$,produce a whistle simultaneously of frequency $300 \; Hz$. Find the number of beats produced. (Assume the speed of sound $v = 332 \; m/s$)

The wavelength is $120 \, cm$ when the source is stationary. If the source is moving with a relative velocity of $60 \, m/s$ towards the observer,then the wavelength of the sound wave reaching the observer will be ... $cm$ (velocity of sound $= 330 \, m/s$).

$A$ source of sound $S$ of frequency $500 \ Hz$ situated between a stationary observer $O$ and a wall $W$,moves towards the wall with a speed of $2 \ m/s$. If the velocity of sound is $332 \ m/s$,then the number of beats per second heard by the observer is (approximately)

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