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1.
2.
3.
A source of sound moves directly towards a stationary observer. The frequency of the sound detected by the observer
is different from the source frequency because
A.
the loudness of the sound increases as the source moves towards the observer.
B.
the apparent wavelength of the sound is longer.
C.
the speed of sound relative to the observer is increased.
D.
the apparent wavelength of the sound is shorter.
A police car, sounding its siren, is travelling at constant speed towards a stationary observer. The sound emitted by
the siren is of constant frequency. The frequency of the sound as heard by the observer is higher than that heard by
the driver of the police car. The reason for this is that
A.
the wavefronts received by the observer are closer together than the wavefronts received by the driver.
B.
the speed of the wavefronts is greater as measured by the observer than by the driver.
C.
the speed of the wavefronts is less as measured by the observer than by the driver.
D.
the wavefronts received by the observer are further apart than the wavefronts received by the driver.
A stationary source emits sound of frequency f0. An observer is moving towards the source at constant speed along
the path indicated by the dotted line. The observer passes very close to the source at time T.
stationary source
observer
Which one of the following graphs best shows the variation with time t of the frequency f heard by the observer?
A.
f
B.
f0
f0
T
C.
t
D.
f
f0
T
t
T
t
f
f0
T
4.
f
t
A point source is moving at a constant speed in a straight-line towards the right and emits sound waves of constant
frequency. The speed of the source is less than the speed of sound. Which of the diagrams correctly shows the
wavefronts emitted by the source?
A.
B.
C.
D.
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5.
A pipe, open at both ends, has a length L. The speed of sound in the air in the pipe is v. The frequency of vibration of
the fundamental (first harmonic) standing wave that can be set up in the pipe is
A.
6.
v
.
2L
B.
L
.
2v
4v
.
L
C.
D.
L
.
4v
A source S produces sound waves of frequency f and is moving along a straight line as shown
below.
I
IV
S
II
III
Which observer I, II, III or IV could hear a sound of frequency f when the source is in the
position shown?
A.
7.
I
B.
II
C.
III
D.
Which one of the following diagrams best represents wavefronts produced by a source of sound
of constant frequency as it moves at constant speed towards a stationary observer at O?
A.
B.
O
C.
O
D.
O
8.
IV
O
The properties of sound waves
Reflection and Refraction
One method of finding the position of fish beneath a boat is to send out a pulse of sound waves
from the bottom of a boat and time how long the pulse takes to return as shown below. The
speed of sound waves in water is 1500 m s–1.
2
water
(a)
emitter and receiver
The time between the pulse
leaving the emitter and
returning to the receiver is
12 ms. Calculate the
distance from the bottom of
the boat to the fish.
fish
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(2)
In order to find fish using this method, the effects of diffraction at the fish need to be minimized.
(b)
(i)
The diagram below shows plane wavefronts incident on an obstacle. Complete the diagram to show
what is meant by diffraction of the wavefronts.
direction of
movement of
wavefronts
(2)
(ii)
Explain why you would expect the effects of diffraction to be negligible when sound of frequency 60
kHz is incident on a large fish.
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(2)
The Doppler effect can be used to determine the speed of an object.
(c)
(i)
Explain what is meant by the Doppler effect.
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(2)
(ii)
A train approaches and then passes by a stationary observer. The train is moving with constant
velocity and emits a sound of constant frequency. The observer hears the frequency change from 490
–1
Hz to 410 Hz. The speed of sound in air is 340 m s . Estimate the speed of the train.
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(4)
(Total 12 marks)
9.
This question is about the Doppler effect.
The diagram below shows wavefronts produced by a stationary wave source S. The spacing of the wavefronts is
equal to the wavelength of the waves. The wavefronts travel with speed V.
S
(a)
The source S now moves to the right with speed
1
V. In the space below, draw four successive wavefronts
2
to show the pattern of waves produced by the moving source.
(3)
(b)
Derive the Doppler formula for the observed frequency f0 of a sound source, as heard by a stationary
observer, when the source approaches the stationary observer with speed v. The speed of sound is V and the
frequency of the sound emitted by the source is f.
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(3)
The Sun rotates about its centre. The light from one edge of the Sun, as seen by a stationary observer, shows a
Doppler shift of 0.004 nm for light of wavelength 600.000 nm.
(c)
Assuming that the Doppler formula for sound may be used for light, estimate the linear speed of a point on
the surface of the Sun due to its rotation.
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(3)(Total 9 marks)
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