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On the same path, the source and observer are moving such a ways that the distance between these two increases with the time. The speeds of source and observer are same and equal to $10 m s^{- 1}$ with respect to ground while no wind is blowing. The apparent frequency received by observer is 1950 Hz, then the original frequency must be (the speed of sound in present medium is 340 $m / s$ )

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Important Questions on Waves

EASY

Physics>Waves and Oscillations>Waves>Doppler Effect

A siren emitting a sound of frequency

800 Hz

moves away from an observer towards a cliff at a speed of

15 m s^{- 1}

. Then, the frequency of sound that the observer hears in the echo reflected from the cliff is
(Take velocity of sound in air

= 330 m s^{- 1}

)

MEDIUM

Physics>Waves and Oscillations>Waves>Doppler Effect

The observer is moving with velocity

v_{0}

towards the stationary source of sound and then after crossing moves away from the source with velocity

v_{0} .

Assume that the medium through which the sound waves travel is at rest. If

v

is the velocity of sound and

n

is the frequency emitted by the source then the difference between apparent frequencies heard by the observer is

MEDIUM

Physics>Waves and Oscillations>Waves>Doppler Effect

A whistle emitting a loud sound of frequency,

540 Hz

is whirled in a horizontal circle of radius,

2 m

and at a constant angular speed of,

15 rad s^{- 1}

. The speed of sound is,

330 m s^{- 1}

. The ratio of the highest to the lowest frequency heard by a listener standing at rest at a large distance from the center of the circle is:

MEDIUM

Physics>Waves and Oscillations>Waves>Doppler Effect

A train

S 1,

moving with a uniform velocity of

108 k m / h,

approaches another train

S 2

standing on a platform. An observer

O

moves with a uniform velocity of

36 k m / h

towards

S 2,

as shown in figure. Both the trains are blowing whistles of same frequency

120 H z .

When

O

600 m

away from

S 2

and distance between

S 1

and

S 2

800 m,

the number of beats heard by

O

is____.

[Speed of the sound

= 330 m s^{- 1}]

MEDIUM

Physics>Waves and Oscillations>Waves>Doppler Effect

A train moves towards a stationary observer with speed

34 m / s .

The train sounds a whistle and its frequency registered by the observer is

f_{1} .

If the speed of the train is reduced to

17 m / s,

the frequency registered is

f_{2} .

If speed of sound is

340 m / s,

then the ratio

f_{1} / f_{2}

is:

EASY

Physics>Waves and Oscillations>Waves>Doppler Effect

Two engines pass each other moving in opposite directions with uniform speed of 30 m/s. one of them is blowing a whistle of frequency 540 Hz. Calculate the frequency heard by driver of second engine before they pass each other. speed of sound is 330 m/sec:

MEDIUM

Physics>Waves and Oscillations>Waves>Doppler Effect

An engine moving away from a vertical cliff blows a born at a frequency

f

. Its speed is

0.5 %

of the speed of sound in air. The frequency of the reflected sound received at engine is

MEDIUM

Physics>Waves and Oscillations>Waves>Doppler Effect

A stationary source emits sound waves of frequency

500 H z

. Two observers moving along a line passing through the source detect sound to be of frequencies

480 H z

and

530 H z

. Their respective speeds are, in

m s^{- 1}

,
(Given speed of sound

= 300 m s^{- 1}

)

MEDIUM

Physics>Waves and Oscillations>Waves>Doppler Effect

A bat moving at

10 m s^{- 1}

towards a wall sends a sound signal of

8000 Hz

towards it. On reflection, it hears a sound of frequency

f

. The value of

f

Hz

is close to

(speed of sound = 320 m s^{- 1})

MEDIUM

Physics>Waves and Oscillations>Waves>Doppler Effect

A source of sound emits sound waves at frequency $f_{0}$ . It is moving towards an observer with fixed speed $v_{s} (v_{s} < v)$ , where $v$ is the speed of sound in air). If the observer were to move towards the source with speed $v_{0}$ , one of the following two graphs (A and B) will give the correct variation of the frequency $f$ heard by the observer as $v_{0}$ is changed.

Question Image

The variation of $f$ with $v_{0}$ is given correctly by:

EASY

Physics>Waves and Oscillations>Waves>Doppler Effect

Two cars A and B are moving away from each other in opposite directions. Both the cars are moving with speed of

20 m s^{- 1}

with respect to the ground. If an observer in car A detects a frequency

2000 H z

of the sound coming from car B, what is the natural frequency of the sound source in car B?
(speed of sound in air

= 340 m s^{- 1}

)

MEDIUM

Physics>Waves and Oscillations>Waves>Doppler Effect

A musician using an open flute of length

50 cm

produces second harmonic sound waves. A person runs towards the musician from another end of a hall at a speed of

10 km h^{- 1}

. If the wave speed is

330 m s^{- 1}

, the frequency heard by the running person shall be close to

MEDIUM

Physics>Waves and Oscillations>Waves>Doppler Effect

Two sources of sound

S_{1}

and

S_{2}

produce sound waves of same frequency

660 H z .

A listener is moving from source

S_{1}

towards

S_{2}

with a constant speed

u_{0} m s^{- 1}

and he hears

10 b e a t s^{- 1}

. The velocity of sound is

330 m s^{- 1} .

Then,

u_{0}

equals:

EASY

Physics>Waves and Oscillations>Waves>Doppler Effect

Two cars moving in opposite directions approach each other with speed of

22 m s^{- 1}

and

16.5 m s^{- 1}

respectively. The driver of the first car blows a horn having a frequency

400 Hz .

The frequency heard by the driver of the second car is [velocity of sound

340 m s^{- 1}

]

MEDIUM

Physics>Waves and Oscillations>Waves>Doppler Effect

A submarine

A

travelling at

18 km {hr}^{- 1}

is being chased along the line of its velocity by another submarine

B

travelling at

27 km {hr}^{- 1}

B

sends a sonar signal of

500 H z

to detect

A

and receives a reflected sound of frequency

v

. The value of

v

is closed to (Speed of sound in water

1500 m s^{- 1}

)

MEDIUM

Physics>Waves and Oscillations>Waves>Doppler Effect

A speeding motorcyclist sees traffic jam ahead of him. He slows down to

36 k m / h o u r .

He finds that traffic has eased and a car moving ahead of him at

18 k m / h o u r

is honking at a frequency of

1392 H z .

If the speed of sound is

343 m / s,

the frequency of the honk as heard by him will be:

EASY

Physics>Waves and Oscillations>Waves>Doppler Effect

A source of sound

S

is moving with a velocity of

50 m s^{- 1}

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

1000 H z .

What will be the apparent frequency of the source when it is moving away from the observer after crossing him? (Take velocity of sound in air is

350 m s^{- 1}

)

EASY

Physics>Waves and Oscillations>Waves>Doppler Effect

An observer is moving with half the speed of light towards a stationary microwave source emitting waves at frequency

10 GHz

. What is the frequency of the microwave measured by the observer? (speed of light

= 3 \times 10^{8} m s^{- 1}

)

MEDIUM

Physics>Waves and Oscillations>Waves>Doppler Effect

A source of sound $S$ emitting waves of frequency $100 Hz$ and an observer $O$ are located at some distance from each other. The source is moving with a speed of $19.4 m s^{- 1}$ at an angle of $60^{o}$ with the source observer line as shown in the figure. The observer is at rest. The apparent frequency observed by the observer corresponding to the wave emitted by the source at the instant shown is

(velocity of sound in air $330 m s^{- 1}$ )

Question Image

HARD

Physics>Waves and Oscillations>Waves>Doppler Effect

A train is moving on a straight track with speed $20 m s^{- 1}$ . It is blowing its whistle at the frequency of $1000 Hz$ . The percentage change in the frequency heard by a person standing near the track as the train passes him is (speed of sound $= 320 m s^{- 1}$ ) close to:

Important Questions on Waves

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