In the figure shown an observer O 1 floats (static) on water surface with ears in air while another observer O 2 is moving upwards with constant velocity V 1 = V 5 in water. The source moves down with constant velocity V s = V 5 and emits sound of frequency f ' . The velocity of sound in air is V and that in water is 4 V . For the situation shown in figure.

The wavelength of the sound received by O 2 is 16 V 5 f .

The wavelength of the sound received by O 1 is V f .

In the figure shown an observer O 1 floats (static) on water surface with ears in air while another observer O 2 is moving upwards with constant velocity V 1 = V 5 in water. The source moves down with constant velocity V s = V 5 and emits sound of frequency f ' . The velocity of sound in air is V and that in water is 4 V . For the situation shown in figure.

The wavelength of the sound received by O 2 is 16 V 5 f .

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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In the figure shown an observer $O_{1}$ floats (static) on water surface with ears in air while another observer $O_{2}$ is moving upwards with constant velocity $V_{1} = \frac{V}{5}$ in water. The source moves down with constant velocity $V_{s} = \frac{V}{5}$ and emits sound of frequency $f^{'} .$ The velocity of sound in air is $V$ and that in water is $4 V$ . For the situation shown in figure.

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Important Questions on Sound Waves and Doppler Effect

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IMPORTANT

PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 1

The average power transmitted across a cross-section by two sound waves moving in the same direction are equal. The wavelengths of two sound waves are in the ratio of

1 : 2

, then find the ratio of their pressure amplitudes.

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PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 3

The intensity of sound from a point source is

1.0 \times 10^{- 8} W / m^{2}

at a distance of

5.0 m

from the source. What will be the intensity at a distance of

25 m

from the source?

(

\times 10^{- 10} W / m^{2})

MEDIUM

Physics

IMPORTANT

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

Two sound sources are moving away from a stationary observer in opposite directions with velocities

V_{1}

V_{1}

and

V_{2} (V_{1} > V_{2})

. The frequency of both the sources is

900 Hz

V_{1}

and

V_{2}

are both quite less than speed of sound,

V = 300 m / s

. Find the value of

(V_{1} - V_{2})

so that beat frequency observed by observer is

9 Hz

. (in

m / s

.).

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Physics

IMPORTANT

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

An ambulance sounding a horn of frequency

264 Hz

is moving towards a vertical wall with a velocity of

5 {ms}^{- 1}

. If the speed of the sound is

330 {ms}^{- 1}

, how many beats per second will be heard by an observer standing a few meters behind the ambulance?

MEDIUM

Physics

IMPORTANT

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

In a car race sound signals emitted by two cars are detected by the detector on the straight track at the end point of the race. Frequency observed is

330 Hz

and

360 Hz

and the original frequency is

300 Hz

of both cars. Race ends with the separation of

100 m

between the cars. Assume both cars move with constant velocity and velocity of sound is

330 m / s

. Find the time taken (in sec) by wining car.

MEDIUM

Physics

IMPORTANT

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

Two tuning forks $A$ and $B$ are vibrating at the same frequency $256 Hz$ . A listener is standing midway between the forks. If both tuning forks move to the right with a velocity of $5 m / s$ , find the number of beats heard per second by the Tistener (speed of sound in air is $330 m / s$ ).

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IMPORTANT

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

A driver in a stationary car horns which produces monochromatic sound waves of frequency $n = 1000 Hz$ , normally towards a reflecting wall. If the wall approaches the car with a velocity $u = 3.3 m / s$ , calculate the frequency of sound reflected from wall and heard by the driver. What is the percentage change of sound frequency on reflection from the wall?

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MEDIUM

Physics

IMPORTANT

PHYSICS FOR JOINT ENTRANCE EXAMINATION WAVES AND THERMODYNAMICS>Chapter 8 - Sound Waves and Doppler Effect>Exercises>Q 13

A source of sound of frequency

256 Hz

is moving towards a wall with a velocity of

5 m / s

. How many beats per second will be heard by an observer

O

standing in such a position that the source

S

is between

O

and wall?

(c = 330 m / s)

Important Questions on Sound Waves and Doppler Effect

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