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 .

MEDIUM

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IMPORTANT

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The frequency changes by $10 %$ as the source approaches a stationary observer with constant speed $v .$ What should be the percentage change in frequency as the source recedes from the observer with the same speed? Given that $v_{s} ≪ v (v$ is the speed of sound in air).

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Important Questions on Sound Waves and Doppler Effect

MEDIUM

Physics

IMPORTANT

PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 23

Speed of sound wave is

v .

If a reflector moves towards a stationary source emitting waves of frequency

f

with speed

u,

the frequency of reflected waves will be

EASY

Physics

IMPORTANT

PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 24

An observer moves towards a stationary source of sound with a speed

{\frac{1}{5}}^{th}

of the speed of sound. The wavelength and frequency of the source are

λ

and

f

, respectively. The apparent frequency and wavelength recorded by the observer are, respectively,

MEDIUM

Physics

IMPORTANT

PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 25

A source of sound

S

is moving with a velocity

50 m s^{- 1}

towards a stationary observer. The observer measures the frequency of the source as

1000 Hz

. What will be the apparent frequency of the source when it is moving away from the observer after crossing him? The velocity of sound in the medium is

350 m s^{- 1}

MEDIUM

Physics

IMPORTANT

PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 26

A whistle emitting a sound of frequency

440 Hz

is tied to a string of

1.5 m

length and rotated with an angular velocity of

20 rad s^{- 1}

in the horizontal plane. Then, the range of frequencies heard by an observer stationed at a large distance from the whistle will be

(v = 330 m s^{- 1})

EASY

Physics

IMPORTANT

PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 27

A man standing on a platform hears the sound of frequency

605 Hz

coming from a frequency

550 Hz

from a train whistle moving towards the platform. If the velocity of sound is

330 m / s

, then what is the speed of train?

EASY

Physics

IMPORTANT

PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 28

A source of sound emits

200 π W

. power which is uniformly distributed over a sphere of radius

10 m

. What is the loudness of sound on the surface of the sphere?

HARD

Physics

IMPORTANT

PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 29

Two cars are moving on two perpendicular roads towards a crossing, with uniform speed of

72 km h^{- 1}

and

36 km h^{- 1}

. If the first car blows horn of frequency

280 Hz

, then the frequency of the horn heard by the driver of second car, when line joining the cars make

45 °

angle with the roads, will be

EASY

Physics

IMPORTANT

PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 30

A sound wave of frequency $n$ travels horizontally to the right with speed $c$ . It is reflected from a broad wall moving to the left with speed $v$ . The number of beats heard by a stationary observer to the left of the wall is

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The frequency changes by 10% as the source approaches a stationary observer with constant speed v. What should be the percentage change in frequency as the source recedes from the observer with the same speed? Given that vs≪v(v is the speed of sound in air).

Important Questions on Sound Waves and Doppler Effect

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The frequency changes by $10 %$ as the source approaches a stationary observer with constant speed $v .$ What should be the percentage change in frequency as the source recedes from the observer with the same speed? Given that $v_{s} ≪ v (v$ is the speed of sound in air).