Two loudspeakers M and N are located 20 m apart and emit sound at frequencies 118 Hz and 121 Hz , respectively. A car is initially at a point P , 1800 m away from the midpoint Q of the line M N and moves towards Q constantly at 60 km h - 1 along the perpendicular bisector of M N . It crosses Q and eventually reaches a point R , 1800 m away from Q . Let ν t represent the beat frequency measured by a person sitting in the car at time t . Let ν p , ν Q and ν R be the beat frequencies measured at locations P , Q and R , respectively. The speed of sound in air is 330 m s - 1 . Which of the following statement(s) is (are) true regarding the sound heard by the person?

The plot below represents schematically the variations of beat frequency with time

Two vehicles, each moving with speed u on the same horizontal straight road, are approaching each other. The wind blows along the road with velocity w . One of these vehicles blows a whistle of frequency f 1 . An observer in the other vehicle hears the frequency of the whistle to be f 2 . The speed of sound in still air is v . The correct statement (s) is (are):

If the wind blows from the source to the observer, f 2 > f 1 .

If the wind blows from the observer to the source, f 2 < f 1 .

If the wind blows from the source to the observer, f 2 < f 1 .

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If the source is moving towards right, wavefront of sound waves get modified to

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Important Questions on Sound Waves and Doppler Effect

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PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 5

Given figure represents the displacement $y$ versus distance $x$ along the direction of propagation of a longitudinal wave. The pressure is maximum at position marked

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PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 6

A tuning fork of frequency $380 Hz$ is moving towards a wall with a velocity of $4 m / s$ . Then the number of beats heard by a stationary listener between direct and reflected sounds will be (velocity of sound in air is $340 m / s$ )

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PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 7

A vehicle with a horn of frequency

n

is moving with a velocity of

30 m s^{- 1}

in a direction perpendicular to the straight line joining the observer and the vehicle. The observer perceives the sound to have a frequency

n + n_{1}

. Then (take velocity of sound in air

330 m s^{- 1}

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PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 8

An isotropic stationary source is emitting waves of frequency

n

and wind is blowing due north. An observer

A

is on north of the source while observer

B

is on south the source. If both the observers are stationary, then

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PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 9

A train is moving with a constant speed along a large circular track. The engine of the train emits a sound of frequency

f .

The frequency heard by the guard at rear end of the train :

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PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 10

An observer moves towards a stationary source of sound, with a velocity one-fifth of the velocity of sound. What is the percentage increase in the apparent frequency?

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PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 11

An engine running at speed

\frac{v}{10}

sounds a whistle of frequency

600 Hz .

A passenger in a train coming from the opposite side at a speed

\frac{v}{15}

experiences this whistle to be of frequency

f^{'}

. If

v

is the speed of sound in the air and there is no wind,

f^{'}

is nearest to

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PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 12

A source of sound produces waves of wavelength

60 cm

when it is stationary. If the speed of sound in air is

320 m / s

and source moves with speed

20 m / s

, the wavelength of sound in the forward direction will be nearest to

If the source is moving towards right, wavefront of sound waves get modified to

Important Questions on Sound Waves and Doppler Effect

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