(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 whistles $A$ and $B$ each have a frequency of $500\,Hz$. $A$ is stationary and $B$ is moving towards the right (away from $A$) at a speed of $50\,m/s$. An observer is between the two whistles moving towards the right with a speed of $25\,m/s$. The velocity of sound in air is $350\,m/s$. Assume there is no wind. Then which of the following statements are true:

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$A$ person carrying a whistle emitting a note of $272 \text{ Hz}$ is running towards a reflecting surface with a speed of $18 \text{ km/h}$. The speed of sound in air is $345 \text{ m/s}$. The number of beats heard by him is:

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$A$ vehicle sounding a whistle of frequency $256 \,Hz$ is moving on a straight road towards a hill with a velocity of $10 \,ms^{-1}$. The number of beats per second observed by a person travelling in the vehicle is (velocity of sound $= 330 \,ms^{-1}$).

DifficultAP EAMCET 2005

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$A$ person observes two moving trains. Train $A$ is reaching the station and train $B$ is leaving the station, both with an equal speed of $30 \text{ m/s}$. If both trains emit sounds with a frequency of $300 \text{ Hz}$, and the speed of sound is $330 \text{ m/s}$, what is the difference in the frequencies heard by the person (in $\text{ Hz}$)?

DifficultMHT CET 2026

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$A$ train whistling at a constant frequency $n_0$ is moving towards a station at a constant speed $v$. The train passes a stationary observer on the station. The frequency $n$ of the sound as heard by the observer is plotted as a function of time $t$. Identify the expected curve.

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$A$ person carrying a whistle emitting a note of $272 \text{ Hz}$ is running towards a reflecting surface with a speed of $18 \text{ km/h}$. The speed of sound in air is $345 \text{ m/s}$. The number of beats heard by him is:

$A$ vehicle sounding a whistle of frequency $256 \,Hz$ is moving on a straight road towards a hill with a velocity of $10 \,ms^{-1}$. The number of beats per second observed by a person travelling in the vehicle is (velocity of sound $= 330 \,ms^{-1}$).

$A$ train whistling at a constant frequency $n_0$ is moving towards a station at a constant speed $v$. The train passes a stationary observer on the station. The frequency $n$ of the sound as heard by the observer is plotted as a function of time $t$. Identify the expected curve.

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