MEDIUM

Earn 100

A source of sound and an observer both move relative to the ground. The frequency of the sound heard by the observer is less than the frequency of source when

50% studentsanswered this correctly

Important Questions on Sound

MEDIUM

Physics>Waves and Oscillations>Sound>Doppler Effect

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):

MEDIUM

Physics>Waves and Oscillations>Sound>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:

MEDIUM

Physics>Waves and Oscillations>Sound>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>Sound>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>Sound>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>Sound>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}

]

EASY

Physics>Waves and Oscillations>Sound>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>Sound>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>Sound>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>Sound>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

EASY

Physics>Waves and Oscillations>Sound>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:

HARD

Physics>Waves and Oscillations>Sound>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:

MEDIUM

Physics>Waves and Oscillations>Sound>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>Sound>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>Sound>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>Sound>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}

)

MEDIUM

Physics>Waves and Oscillations>Sound>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:

MEDIUM

Physics>Waves and Oscillations>Sound>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})

EASY

Physics>Waves and Oscillations>Sound>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}

)

EASY

Physics>Waves and Oscillations>Sound>Doppler Effect

When the source of sound moves towards a stationary observer, the wavelength of sound received by him

A source of sound and an observer both move relative to the ground. The frequency of the sound heard by the observer is less than the frequency of source when

Important Questions on Sound

Learn and Prepare for any exam you want !