1
The audible range of a girl's hearing is 30 Hz to 16 500 Hz. If the speed of sound in air is 330 m
s−1, what is the shortest wavelength of sound in air which the girl can hear?
m
A
B
m
C
m
m
D
(Total 1 mark)
2
Explain briefly how transmission of energy by a transverse wave differs from transmission by a
longitudinal wave.
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
.................................................................................................................................
(Total 2 marks)
3
(a)
(i)
State the difference between a longitudinal wave and a transverse wave.
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
(2)
(ii)
State an example of a transverse wave.
...............................................................................................................
(1)
(iii)
State an example of a longitudinal wave.
...............................................................................................................
(1)
Page 1 of 35
(b)
Sound with a frequency of 560 Hz travels through steel with a speed of 4800 m s–1.
Calculate the wavelength of the sound wave.
(2)
(Total 6 marks)
4
(a)
When an earthquake occurs longitudinal waves (P waves) and transverse waves (S
waves) are produced in the Earth’s crust. The P waves travel faster than the S waves. A
station, whose task is to detect and locate the position of earthquakes, is at a distance d
from the point where the earthquake originates (the epicentre).
The speed of P waves is 7.5 km s–1 and that of S waves is 5.0 km s–1 . For a particular
earthquake the station detects the P wave 1.5 s before the S wave.
(i)
Write down expressions for the time it takes each wave to travel the distance d from
the epicentre to the station.
Time for P waves ..................................................................................
Time for S waves ...................................................................................
(1)
(ii)
Determine the distance of the epicentre from the station.
(2)
(b)
The earthquake can set up resonant vibrations in bridges causing them to collapse. The
diagram below shows one such bridge. The modes of vibration of the bridge are similar to
those of a stretched string.
(i)
Explain how a stationary wave is set up in a stretched string.
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
(2)
(ii)
The velocity of transverse waves along the bridge is 180 m s–1. Determine the
frequency of the vibrations produced by an earthquake that would cause the central
span of the bridge to resonate at its fundamental frequency (first harmonic).
(3)
Page 2 of 35
(iii)
A designer assumes the highest frequency produced by an earthquake is 1.5 times
the fundamental frequency and decides to modify the bridge by building an extra
support midway between the two existing supports.
Explain whether this modification would eliminate resonant vibrations caused by an
earthquake.
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
...............................................................................................................
(2)
(Total 10 marks)
5
(a)
State the difference between transverse and longitudinal waves.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(2)
(b)
State what is meant by polarisation.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(2)
(c)
Explain why polarisation can be used to distinguish between transverse and longitudinal
waves.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(2)
(Total 6 marks)
Page 3 of 35
6
Polarization is a property of one type of wave.
(a)
Circle below the type of wave that can be polarized.
transverse
longitudinal
(1)
(b)
Give one example of the type of wave that can be polarized.
........................................................................................................................
(1)
(c)
Explain why some waves can be polarized but others cannot. Space is provided for
sketches should you wish to include them in your answer.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(3)
(Total 5 marks)
7
Figure 1 shows three particles in a medium that is transmitting a sound wave. Particles A and C
are separated by one wavelength and particle B is half way between them when no sound is
being transmitted.
Figure 1
(a)
Name the type of wave that is involved in the transmission of this sound.
........................................................................................................................
(1)
(b)
At one instant particle A is displaced to the point A' indicated by the tip of the arrow in
Figure 1. Show on Figure 1 the displacements of particles B and C at the same instant.
Label the position B' and C' respectively.
(1)
Page 4 of 35
(c)
Explain briefly how energy is transmitted in this sound wave.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(2)
(Total 4 marks)
8
(a)
With the aid of a clearly labelled diagram explain how a sound wave in air transmits energy
away from its source.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(3)
Page 5 of 35
(b)
Unlike sound waves, transverse waves can be polarised. Give one example of a
transverse wave and draw a diagram to show how it can be plane polarised. State a
method of polarising a wave of the type you have chosen.
Example transverse wave ........................................
Method of polarisation .......................................................
(3)
(Total 6 marks)
9
Which one of the following types of wave cannot be polarised?
A
radio
B
ultraviolet
C
microwave
D
ultrasonic
(Total 1 mark)
10
Which one of the following types of wave cannot be polarised?
A
radio
B
ultrasonic
C
microwave
D
ultraviolet
(Total 1 mark)
Page 6 of 35
11
The term ultrasound refers to vibrations in a material that occur at frequencies too high to be
detected by a human ear. When ultrasound waves move through a solid, both longitudinal and
transverse vibrations may be involved. For the longitudinal vibrations in a solid, the speed c of
the ultrasound wave is given by
where E is the Young modulus of the material and ρ is the density. Values for c and ρ are given in
the table below.
Substance
c / m s−1
ρ / kg m−3
glass
5100
2500
sea water
1400
1000
Ultrasound waves, like electromagnetic radiation, can travel through the surface between two
materials. When all the energy is transmitted from one material to the other, the materials are
said to be acoustically matched. This happens when ρc is the same for both materials.
(a)
Calculate the magnitude of the Young modulus for glass.
Young modulus = ...............................
(1)
(b)
State your answer to (a) in terms of SI fundamental units.
(1)
Page 7 of 35
(c)
The passage states that ’when ultrasound waves move through a solid both longitudinal
and transverse vibrations may be involved’.
State the difference between longitudinal and transverse waves.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(2)
(d)
Show that when two materials are acoustically matched, the ratio of their Young moduli is
equal to the ratio of their speeds of the ultrasound waves.
(2)
(e)
The wave speed in a material X is twice that in material Y. X and Y are acoustically
matched.
Determine the ratio of the densities of X and Y.
X = ............................... Y = ...............................
(1)
Page 8 of 35
(f)
Ultrasound waves obey the same laws of reflection and refraction as electromagnetic
waves.
Using data from Table 1, discuss the conditions for which total internal reflection can occur
when ultrasound waves travel between glass and sea water.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(3)
(Total 10 marks)
12
(a)
State the characteristic features of
(i)
longitudinal waves,
.............................................................................................................
.............................................................................................................
(ii)
transverse waves.
.............................................................................................................
.............................................................................................................
(3)
(b)
Daylight passes horizontally through a fixed polarising filter P. An observer views the light
emerging through a second polarising filter Q, which may be rotated in a vertical plane
about point X as shown in Figure 1.
Figure 1
Page 9 of 35
Describe what the observer would see as Q is rotated slowly through 360°.
You may be awarded marks for the quality of written communication provided in
your answer.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(2)
(Total 5 marks)
13
Which line, A to D, in the table shows correct relationships for the respective wavelengths, λL, λS,
and frequencies, fL, fS, of light waves and sound waves?
wavelengths
frequencies
A
λL << λS
fL >> fS
B
λL << λS
fL << fS
C
λL >> λS
fL >> fS
D
λL >> λS
fL << fS
(Total 1 mark)
14
Which one of the following properties of light waves do polarising sunglasses depend on for their
action?
Light waves may
A
interfere constructively.
B
interfere destructively.
C
be polarised when reflected from a surface.
D
be polarised by the lens in the eye.
(Total 1 mark)
Page 10 of 35
15
By approximately how many times is the wavelength of audible sound waves greater than the
wavelength of light waves?
A
102
B
106
C
1010
D
1014
(Total 1 mark)
16
The sound quality of a portable radio is improved by adjusting the orientation of the aerial.
Which statement is a correct explanation of this improvement?
A
The radio waves from the transmitter are polarised.
B
The radio waves from the transmitter are unpolarised.
C
The radio waves become polarised as a result of adjusting the aerial.
D
The radio waves become unpolarised as a result of adjusting the aerial.
(Total 1 mark)
17
(a)
Define the amplitude of a wave.
......................................................................................................................
......................................................................................................................
(1)
(b)
(i)
Other than electromagnetic radiation, give one example of a wave that is transverse.
.............................................................................................................
(1)
(ii)
State one difference between a transverse wave and a longitudinal wave.
.............................................................................................................
.............................................................................................................
(1)
Page 11 of 35
(c)
The figure below shows two identical polarising filters, A and B, and an unpolarised light
source. The arrows indicate the plane in which the electric field of the wave oscillates.
(i)
If polarised light is reaching the observer, draw the direction of the transmission axis
on filter B in the figure below.
(1)
(ii)
The polarising filter B is rotated clockwise through 360º about line XY from the
position shown in the figure above. On the axes below, sketch how the light intensity
reaching the observer varies as this is done.
(2)
Page 12 of 35
(d)
State one application, other than in education, of a polarising filter and give a reason for its
use.
......................................................................................................................
......................................................................................................................
......................................................................................................................
......................................................................................................................
(2)
(Total 8 marks)
18
Complete the first column in the table to show which of the waves listed are transverse and which
are longitudinal.
Complete the second column to show which waves can be polarised.
type of wave
transverse or
longitudinal
can be polarised
(answer yes or no)
light
microwaves
ultrasound
(Total 3 marks)
Page 13 of 35
19
The figure below shows two ways in which a wave can travel along a slinky spring.
(a)
State and explain which wave is longitudinal.
........................................................................................................................
........................................................................................................................
(2)
(b)
On the figure above,
(i)
clearly indicate and label the wavelength of wave B
(1)
(ii)
use arrows to show the direction in which the points P and Q are about to move as
each wave moves to the right.
(2)
(c)
Electromagnetic waves are similar in nature to wave A.
Explain why it is important to correctly align the aerial of a TV in order to receive the
strongest signal.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(2)
(Total 7 marks)
Page 14 of 35
20
Earthquakes produce transverse and longitudinal seismic waves that travel through rock. The
diagram below shows the displacement of the particles of rock at a given instant, for different
positions along a transverse wave.
(a)
State the phase difference between
(i)
points A and B on the wave ...................................................................
(ii)
points A and C on the wave ...................................................................
(2)
(b)
Describe the motion of the rock particle at point B during the passage of the next complete
cycle.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(2)
(c)
A scientist detects a seismic wave that is polarised. State and explain what the scientist
can deduce from this information.
........................................................................................................................
........................................................................................................................
........................................................................................................................
(2)
Page 15 of 35
(d)
The frequency of the seismic wave is measured to be 6.0 Hz.
(i)
Define the frequency of a progressive wave.
...............................................................................................................
...............................................................................................................
(1)
(ii)
Calculate the wavelength of the wave if its speed is 4.5 × 103 m s–1.
wavelength .......................................... m
(2)
(Total 9 marks)
21
Ultrasound waves are used to produce images of a fetus inside a womb.
(a)
Explain what is meant by the frequency of a wave.
........................................................................................................................
........................................................................................................................
........................................................................................................................
(1)
(b)
Ultrasound is a longitudinal wave. Describe the nature of a longitudinal wave.
........................................................................................................................
........................................................................................................................
........................................................................................................................
(2)
(c)
In order to produce an image with sufficient detail, the wavelength of the ultrasound must
be 0.50 mm. The speed of the ultrasound in body tissue is 1540 m s–1. Calculate the
frequency of the ultrasound at this wavelength.
Give your answer to an appropriate number of significant figures.
frequency ........................................ Hz
(2)
Page 16 of 35
(d)
A continuous ultrasound wave of constant frequency is reflected from a solid surface and
returns in the direction it came from.
Assuming there is no significant loss in amplitude upon reflection, describe and explain the
effect the waves have on the particles in the medium between the transmitter and the solid
surface.
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
........................................................................................................................
(3)
(Total 8 marks)
22
Which one of the following provides direct experimental evidence that light is a transverse wave
motion rather than a longitudinal wave motion?
A
Two light waves that are coherent can be made to interfere.
B
Light can be diffracted.
C
Light can be polarised.
D
The intensity of light from a point source falls off inversely as
the
square of the distance from the source.
(Total 1 mark)
Page 17 of 35
23
Which of the following waves cannot be polarised?
A
radio
B
ultrasonic
C
microwave
D
ultraviolet
(Total 1 mark)
Page 18 of 35
Mark schemes
1
2
C
[1]
disturbance / oscillation / vibration is pendendicular to same directions for transverse and parallel
to the direction for longitudinal waves
M1
clear indication of what the direction of reference is eg direction of propagation,
transmission of the wave or energy / direction in which the wave is travelling
A1
(2)
[2]
3
(a)
(i)
loose distinction e.g. one has oscillations parallel to the wave direction and the other
has oscillations in the same direction as the wave
C1
transverse -vibrations perpendicular to direction of propagation
longitudinal -vibrations in same direction as direction of propagation
A1
(2)
(ii)
any example of transverse wave
B1
(1)
(iii)
any example of longitudinal wave
B1
(1)
(b)
v = fλ
C1
8.6 m
A1
(2)
[6]
4
(a)
(i)
d / 7.5 and d / 5.0 (denominator may be in m s–1)
or d / 7.5 and d / 7.5 + 1.5
or d / 5.0 – .5 and d / 5.0
B1
(1)
(ii)
d / 7.5 + 1.5 = d / 5.0
C1
22.5 (22 – 23) km
A1
(2)
Page 19 of 35
(b)
(i)
interference / superposition of waves (condone waves superimpose) of:
same frequency travelling in opposite directions
or an incident and a reflected wave
B1
idea of a resonant length
eg length of string is a whole number of half wavelengths of the wave
or length such as to produce nodes and antinodes
or fixed ends are nodes
B1
(2)
(ii)
wavelength of fundamental = 64 m
C1
v = fλ
C1
2.8 Hz
A1
(3)
(iii)
(natural / fundamental) frequency of oscillation of the new spans
= 2 × (ii) (5.6 Hz) or twice original frequency
or wavelength is half the original wavelength(= 32 m)
M1
clear link and conclusion shown between the new natural frequency of the
spans
and the max frequency of the earthquake
examples:
second calculation plus conclusion that resonant vibrations would
not take place
or calculation and comparison of the wavelength of the
earthquake wave travelling along the bridge and the resonant
wavelength (42 m and 32 m)
A1
(2)
[10]
Page 20 of 35
5
(a)
transverse: vibration / displacement / disturbance not movement is
perpendicular to direction of travel
B1
longitudinal: vibration / displacement / disturbance not movement
is parallel to (same) direction of travel
B1
C1 for idea of transverse and longitudinal being perpendicular
(2)
(b)
restriction of vibration / idea of how polarisation occurs
B1
single plane / same orientation – diagram may help
B1
(2)
(c)
only transverse can be polarised / longitudinal cannot
B1
idea of being able to restrict vibration to single plane
or longitudinal not being perpendicular to motion
or longitudinal vibrating in direction of travel
B1
(2)
[6]
6
(a)
Transverse
B1
(b)
correct example of transverse wave
( e.g. light / electromagnetic / radio etc. allow photon b.o.d.)
B1
(c)
[transverse] displacement vector perpendicular to energy
direction [accept ‘direction of motion’]
B1
[longitudinal] vector parallel to energy direction
B1
polarisation is restriction of displacement vector to one
plane OWTTE
[allow any or all marks on clear diagram]
B1
[5]
7
(a)
longitudinal wave
B1
1
(b)
arrows showing B displaced to the left and C to the right
B1
1
Page 21 of 35
(c)
particles in the transmitting medium are made to vibrate/given
energy
B1
or
mention of a compression/region of increased pressure (or
rarefaction)
cause nearby particles to vibrate/have energy/move
B1
or
the compression produces a compression further along (the
medium)
2
[4]
8
(a)
Good diagram of pressure variations/particle oscillations
with at least one label indicating direction of propagation,
pressure variation or density variation
B1
Plus any two from five of
Vibrating source
B1
Energy transferred to (air) molecules
B1
Energy passed on by collisions between molecules
B1
Oscillations of air molecule neighbours slightly out
of phase
B1
Oscillations/waves are longitudinal/energy transfer parallel
to vibrations
B1
3
Page 22 of 35
(b)
Diagram showing several transverse vibrations/waves which are
subsequently limited to one after polarisation
B1
Valid example (light, microwaves etc.)
accept sunlight
Suitable polariser for the stated example
M1
(polaroid, reflection, metal grid etc). Not sunglasses
A1
3
[6]
9
10
11
D
[1]
B
[1]
(a)
6.5 × 1010 Pa ✓
1
(b)
kg m-1 s-2 ✓
1
(c)
Direction of movement of particles in transverse wave perpendicular to energy
propagation direction✓
1
Parallel for longitudinal✓
1
(d)
ρ1c1=ρ2c2✓
E=ρc2 or ρc =
seen
1
1
Page 23 of 35
(e)
[
and cx = 2cy ]
0.5✓
1
(f)
speed of the wave in seawater is less than speed of the wave in glass✓
1
argument to show that watern glass <1✓
1
so tir could be observed when wave moves from water to glass ✓
1
[10]
12
(a)
(i)
particle vibration (or disturbance or oscillation) (1)
same as (or parallel to) direction of propagation
(or energy transfer) (1)
(ii)
(particle vibration)
perpendicular to direction of propagation (or energy transfer) (1)
3
(b)
variation in intensity between max and min (or light and dark) (1)
two maxima (or two minima) in 360° rotation (1)
2
QWC 1
[5]
13
14
15
16
A
[1]
C
[1]
B
[1]
A
[1]
Page 24 of 35
17
(a)
maximum displacement from equilibrium/mean
position/mid-point/etc (1)
1
(b)
(i)
any one from:
surface of water/water waves/in ripple tank (1)
rope (1)
slinky clearly qualified as transverse (1)
secondary (‘s’) waves (1)
max 1
(ii)
transverse wave: oscillation (of medium) is perpendicular to
wave travel
or transverse can be polarised
or all longitudinal require a medium (1)
1
(c)
(i)
vertical line on B ± 5° (1)
1
(ii)
max 0, 180, 360 + min 90, 270 (1)
and line reaches same minimum and maximum every time
and reasonable shape (1)
2
Page 25 of 35
(d)
appropriate use (1)
reason for Polaroid filter being used (1)
eg
Polaroid glasses/sunglasses/
to reduce glare
windscreens
camera
reduce glare/enhance image
(in a) microscope
to identify minerals/rocks
polarimeter
to analyse chemicals/concentration
or type of sugar
stress analysis
reveals areas of high/low stress/
other relevant detail
LCD displays
very low power/other relevant
detail
3D glasses
enhance viewing experience, etc
2
[8]
18
transverse
yes
B1
transverse
yes
B1
longitudinal
no
B1
[3]
Page 26 of 35
19
(a)
(wave) B
(the parts of the) spring oscillate / move back and forth in direction of / parallel
to wave travel
OR
mention of compressions and rarefactions
Second mark can only be scored if first mark is scored
2
(b)
(i)
(double ended arrow / line / brackets) from between two points in phase
1
(ii)
wave A: arrow vertically upwards
wave B: arrow horizontally to the left
2
(c)
(transmitted radio waves are often) polarised
aerial (rods) must be aligned in the same plane (of polarisation / electric field) of
the wave
2
[7]
20
(a)
(i)
π / 2 (radians) or 90 (degrees)
No path differences
Penalise contradictions
No fractions of a cycle
1
(ii)
3π / 2 (rad) or 270 (degrees)
No path differences
Penalise contradictions
No fractions of a cycle
1
(b)
(oscillation or motion) perpendicular to direction of wave (travel / velocity / energy
transfer)
(oscillates from equilibrium to maximum positive displacement, back to equilibrium,
then to max negative displacement) and back to equilibrium / starting position / rest
position
do not allow ‘up and down’ for first mark
allow ‘up and down’, or ‘down then up’, ‘side to side’, ‘rise and fall’
in place of oscillates
Allow ‘rest position’, ‘starting position’ ,‘middle’, ‘centre line’
ref to nodes / antinodes not allowed for 2 nd mark
2
Page 27 of 35
(c)
(the wave is) transverse OR not longitudinal
accept it is an S wave or secondary wave
only transverse can be polarised OR longitudinal waves cannot be polarised
OR oscillations are in one plane
2
(d)
(i)
number of waves / complete cycles / wavelengths (passing a point / produced)
per second
or ‘unit time’
allow: (number of) oscillations / vibrations / cycles per second
allow f=1 / T only if T is correctly defined
do not allow references to f=c / λ
1
(ii)
( v = f / λ λ = v / f = ) 4.5 × 103 / 6.0
= 750 (m)
correct answer only gets 2 marks
2
[9]
21
(a)
number of (complete) waves (passing a point) in 1 second
OR
number of waves / time (for the waves to pass a point)
OR
(complete number of) oscillations \ vibrations per second
OR
1 / T with T defined as time for 1 (complete) oscillation ✓
Allow: cycles
Allow: unit time
1
Page 28 of 35
(b)
For two marks:
oscillation of particles \ medium \ material etc, but not oscillation of wave is parallel to
\ in same direction as
the direction wave (travels) ✓ ✓
For one mark:
particles \ material \ medium move(s) \ disturbance \ displacement
parallel to \ in same direction as
the direction wave travels
OR
(oscillations) parallel to direction of wave travel ✓
the one mark answer with:
mention of compressions and rarefactions
OR
(longitudinal waves) cannot be polarised
gets two marks
✓
Allow
Vibration
Allow direction of energy transfer \ wave propagation
2
(c)
( f = 1540 / 0.50 × 10−3 )
= 3 100 000 (Hz) ✓ (3 080 000)
2sf ✓
2
(d)
no more than two points from either list (max 3):
Description
• mention of nodes and antinodes
• particles not moving at a node
• maximum displacement at antinode
• particles either side of node in antiphase / between two nodes in phase
• variation of amplitude between nodes
Explanation
• a stationary wave (forms)
• two waves are of equal frequency or wavelength (and amplitude in the same
medium)
• reflected and transmitted waves \ waves travelling in opposite directions, pass
through each other
• superpose / interference occurs
• constructive interference at antinodes
• destructive interference at nodes
✓✓✓
Allow ‘standing wave’
3
[8]
Page 29 of 35
22
23
C
[1]
B
[1]
Page 30 of 35
Examiner reports
2
5
6
7
Candidates seemed to find this difficult to express clearly and unambiguously. A common
response was that energy moves perpendicular to the direction of travel of the wave if transverse
or in the direction of the wave if longitudinal. There seems to be inadequate appreciation that
waves represent a flow of energy through the medium whatever its form and that it is the motion
of the particles in the medium that provides the difference. A clear mention of something
oscillating would enhance many responses.
(a)
Most candidates were able to show that they knew and understood the differences between
transverse and longitudinal waves. Weaker candidates confused their answers by giving
unclear statements such as ‘…transverse waves move at right angles to their direction of
travel whilst longitudinal move in a parallel direction’ .
(b)
Answers were often unclear and candidates tended to focus on the polarisation of light
waves, often going on to talk about the effect of crossed polaroids in their answers. Most
candidates recognised that transverse waves can be polarised but there was some
confusion about why longitudinal waves cannot.
(c)
Answers were often unclear and candidates tended to focus on the polarisation of light
waves, often going on to talk about the effect of crossed polaroids in their answers. Most
candidates recognised that transverse waves can be polarised but there was some
confusion about why longitudinal waves cannot.
(a)
Almost all candidates knew that transverse waves could be polarised.
(b)
Almost all could give a clear, correct example of a wave that can be polarised.
(c)
Explanations of why some waves can be polarised were weaker. Not only were the
descriptions of the wave types muddled and poor, but many failed to describe clearly why
longitudinal waves cannot be polarised. A large number would have helped themselves by
drawing clear well labelled diagrams.
(a)
Very few did not know the type of wave although the spelling of longitudinal was often very
poor.
(b)
This was done very poorly with the majority incorrectly showing displacements of both
particles to the right
(c)
Most were able to gain at least one mark here and many gained both. Lack of clarity in the
response was often the cause of loss of the second mark.
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In part (a) diagrams and explanations varied from excellent to non-existent. The best candidates
provided a well-labelled diagram of an oscillating source radiating a longitudinal wave in air. They
went on to write about the vibrations of the source being passed on to the air molecules around
it, and the energy being propagated as the result of collisions between oscillating molecules.
Part (b) was quite often answered well, but some candidates confused polarisation with
diffraction and referred to a polarising slit for visible light.
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Reluctance to memorise conventional definitions meant that many candidates were struggling to
construct an answer in part (a). This usually caused a failure to express ideas sufficiently clearly
for any marks to be awarded - for example “the waves move along in the same direction as the
wave is travelling”. Part (b) was generally very well answered, although there were references to
coloured effects and/or fringes in some scripts. The most frequent mistake amongst more
successful candidates was the notion that successive maxima of intensity occurred every 360° of
rotation, rather than every 180°.
In part (a), the strict definition of amplitude was expected. Candidates needed to say ‘maximum
displacement’ and then indicate in some way that this was relative to the equilibrium position.
The majority, however, chose to define amplitude as the distance between the centre and the
peak.
For part (b) (i), the majority of candidates could not give an example of a transverse wave other
than electromagnetic waves. Most gave a form of electromagnetic radiation (most commonly
‘light’) or even sound. Common answers that were accepted included ‘water waves’, ‘waves on
strings’ or ‘s-waves’.
Most candidates realised that a comparison between the direction of wave travel and the
oscillation of the medium was a good way to answer part (b) (ii). It was common, however, for
candidates to struggle to express this clearly. The most common error was to say that a
transverse wave ‘moves’ perpendicular to the direction of wave travel rather than ‘oscillation is
perpendicular to direction of wave travel’.
The vast majority of candidates found part (c) (ii) very straight forward.
The majority of candidates had no problem with part (c) (ii). The exact shape of the line was not
important as long as the maximum and minimum intensities appeared in the right place.
There were many very good answers to part (d), such as ‘sunglasses/ski goggles reduce glare
from light reflected from water/snow’ and ‘a camera filter reduces unwanted reflections’. Common
inadequate responses included saying that polarising sunglasses ‘reduce light intensity’ because
the lenses are ‘darker’, or that polarising filters reduce UV.
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This question was answered well by many, who understood that all electromagnetic waves are
transverse and therefore can be polarised whilst ultrasound, like sound, is longitudinal and
therefore cannot be polarised.
Most did well in part (b)(i) and indicated a complete wavelength very precisely, though a
generous tolerance was allowed. A significant number thought the coils constituted the waveform
and gave the spacing between one or two coils as the wavelength and some chose the
compression or the rarefaction or the whole length of the spring. In part (b)(ii) many believed
point P would move downwards. This is a very common misconception and a similar question
has appeared in a past paper. The behaviour of point Q is more difficult to understand. The
particle changes direction when the centre of a rarefaction or compression reaches it. If the wave
is moving to the right, then as the compression gets closer to the particle, the particle will move
left towards the compression.
In (c) the majority of students surprisingly did not recognise that this was about polarisation.
Those who did point this out did not describe the aerial being aligned with the plane of
polarisation.
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(a)
(i)
Some candidates thought this was a stationary wave and thus stated incorrect phase
differences. See (a)(ii).
(ii)
Phase difference is generally not well understood by candidates. Phase differences
were often wrongly given in fractions of a wavelength e.g. λ / 4 rather than angles,
e.g. 90°. Ninety degrees was often also given as π / 4 radians or π radians rather than
π / 2 radians. Two hundred and seventy degrees was often thought to be equivalent
to π rather than 3 / 2 π radians.
Many said ‘in phase’ or ‘out of phase’ rather than stating the phase difference.
Many marks were lost here due to contradictions, where candidates attempting to
embellish their answers only succeeded in talking themselves out of the mark. E.g.’
90° (π / 4)’ or ‘90° (antiphase) ’. Where a question says ‘state’ and there is one mark
available, the candidate should try to give just the answer that they are confident is
correct and not try to expand upon it.
(b)
A high proportion of candidates thought that point B was going to go ‘downwards’.
Candidates must be clearer when stating directions. It is always advisable to say ‘vertically
upwards’ or ‘move upwards perpendicularly to the equilibrium line’. When a description of a
complete cycle is required, marks will be lost if the whole cycle is not described including,
in this case, the return to the equilibrium position.
(c)
Many came up with interesting hypotheses such as, that the wave must have passed
through a ‘crack’ in the rock to become polarised. However, in a question like this we are
only expecting the candidate to apply the physics that they know. Here we were only
looking for the link between polarisation and transverse waves, and not an in depth
knowledge of seismology.
(d)
This was very well done. A few candidates defined time period (T) rather than frequency.
There was a tendency for some to say ‘number of waves that pass a point in a given time’
rather than per second. A rather odd response to this question that was seen quite often
was: ‘The frequency doesn’t change’ . Quite a few stated the equation f = c/λ but this is not
the accepted definition of frequency.
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(a)
The majority of candidates got this mark and only a small number missed out the very
important ‘per second’.
(b)
For 2 marks it was necessary to point out that the particles are oscillating rather than the
wave oscillating. For example, some candidates said something like, ‘ waves oscillate
parallel to direction of wave’, or ‘ the motion is in the direction of the wave’.
Confusion between progressive waves and stationary waves was often seen and some
candidates talked about ‘ energy not being transferred with the wave’.
Many candidates talk about ‘motion’ of particles rather than oscillation. Part (a) and part (b)
highlight the fact that simple descriptions and definitions need to be memorised.
(c)
The first part was done well apart from some candidates who did not convert from mm to
m. Many rounded to 3sf rather than 2. This was probably because they believed 0.50 mm
was three significant figures.
(d)
This type of question is asking the student to apply their knowledge in a context that may
be unfamiliar (assessment objective AO2 – see specification).
A simple explanation describing the formation of a stationary wave was therefore needed
here.
However, many students did not spot that the question was about stationary waves.
Candidates could mention how nodes and antinodes are formed by superposition, etc.
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