(D) The Doppler effect formula is given by $n' = n \left( \frac{v \pm v_o}{v \mp v_s} \right)$.For whistle $A$ (source stationary,$v_s = 0$) and obser

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(D) The Doppler effect formula is given by $n' = n \left( \frac{v \pm v_o}{v \mp v_s} \right)$.For whistle $A$ (source stationary,$v_s = 0$) and observer moving away at $25\,m/s$ $(v_o = 25\,m/s)$: $n'_A = 500 \left( \frac{350 - 25}{350} \right) = 500 \times \frac{325}{350} \approx 464.28\,Hz$.For whistle $B$ (source moving away at $50\,m/s$,$v_s = 50\,m/s$) and observer moving towards it at $25\,m/s$ $(v_o = 25\,m/s)$: $n'_B = 500 \left( \frac{350 + 25}{350 + 50} \right) = 500 \times \frac{375}{400} = 468.75\,Hz$.Difference in frequencies heard by the observer: $\Delta n = |n'_B - n'_A| = |468.75 - 464.28| = 4.47\,Hz \approx 4.5\,Hz$.Thus,statements $(B)$ and $(C)$ are correct.

Class 11 Physics Waves and Sound Doppler’s Effect

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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:

A
The apparent frequency of whistle $B$ as heard by $A$ is $444\,Hz$ approximately.
B
The apparent frequency of whistle $B$ as heard by the observer is $469\,Hz$ approximately.
C
The difference in the apparent frequencies of $A$ and $B$ as heard by the observer is $4.5\,Hz$.
D
Both $(B)$ and $(C)$.

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Waves and Sound

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Doppler’s Effect

An observer standing at a station observes a frequency of $219 \, Hz$ when a train approaches and $184 \, Hz$ when the train goes away from him. If the velocity of sound in air is $340 \, m/s$,then the velocity of the train and the actual frequency of the whistle will be:

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$A$ stationary source is emitting sound at a fixed frequency $f_0$,which is reflected by two cars approaching the source. The difference between the frequencies of sound reflected from the cars is $1.2\%$ of $f_0$. What is the difference in the speeds of the cars (in $km/h$) to the nearest integer? The cars are moving at constant speeds much smaller than the speed of sound,which is $330 \ m/s$.

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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 $v = 332 \; m/s$)

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$A$ man is watching two trains,one leaving and the other coming with an equal speed of $4\,m/s$. If they sound their whistles each of frequency $240\,Hz$,the number of beats per second heard by the man will be equal to: (velocity of sound in air $= 320\,m/s$)

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$A$ racing car moving towards a cliff sounds its horn. The driver observes that the sound reflected from the cliff has a pitch one octave higher than the actual sound of the horn. If $v$ is the velocity of sound,the velocity of the car will be

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An observer standing at a station observes a frequency of $219 \, Hz$ when a train approaches and $184 \, Hz$ when the train goes away from him. If the velocity of sound in air is $340 \, m/s$,then the velocity of the train and the actual frequency of the whistle will be:

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 $v = 332 \; m/s$)

$A$ man is watching two trains,one leaving and the other coming with an equal speed of $4\,m/s$. If they sound their whistles each of frequency $240\,Hz$,the number of beats per second heard by the man will be equal to: (velocity of sound in air $= 320\,m/s$)

$A$ racing car moving towards a cliff sounds its horn. The driver observes that the sound reflected from the cliff has a pitch one octave higher than the actual sound of the horn. If $v$ is the velocity of sound,the velocity of the car will be

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