GCE EXAMINERS' REPORTS
AS PHYSICS (NEW)
SUMMER 2016
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Unit
Page
Motion, energy and matter
1
Electricity and light
6
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PHYSICS
General Certificate of Education
Summer 2016
Advanced Subsidiary/Advanced
UNIT 1 – MOTION, ENERGY AND MATTER
General comments:
This was the first unit 1 examination to be sat based on the new specification. The
examination contained questions from all sections of the specification along with, and for the
first time in a theory paper, questions specifically related to experimental technique, data
handling and uncertainty analysis. In addition, questions were set to test candidates’ ability
to provide accurate, logical and well-constructed extended responses and also to test
candidates’ understanding of ethical issues related to science in our society. All of these
changes are requirements of the new specification. Questions based on other, more familiar
topics such as kinematics, work-energy and, though from different module areas in the
previous specification, momentum, the physics of materials, stellar physics and particles
were also set.
Examiners felt that candidate responses were, on the whole, encouraging. Questions which
scored highly included the more familiar topics of particles, materials and work-energy.
Questions which did not score as highly included uncertainty analysis and momentum.
Further details are provided below.
Candidates displayed good mathematical skills, especially in substituting and re-arranging
equations. A significant minority of candidates made simple errors in reading scales
however. This was particularly evident in questions 3, 4 and 7 where many candidates did
not take sufficient care when interpreting the numerical values associated with the graph
scales provided. Examiners felt that candidates had a good understanding of significant
figures.
Examiners commented favourably on candidates’ ability to communicate ideas clearly and
succinctly. Responses to the QER question in particular were, on the whole, clear,
unambiguous and logically structured. Spelling, punctuation and grammar was usually very
good.
Specific comments:
Q.1
(a)
(i)&(ii) This was the first time that questions testing knowledge and
application of experimental uncertainties had been set on a theory
paper. It was apparent that candidates who had been prepared for this
coped very well. Successful candidates used a variety of approaches
to determine the percentage uncertainty in the density including, in
some cases, finding the maximum and minimum values of density and
(max value - min value)
then applying: uncertainty =
2
and then using this value to determine the percentage uncertainty.
© WJEC CBAC Ltd.
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Most candidates however used the more conventional approach of
adding the percentage uncertainty in each of the volume and mass to
determine the total uncertainty in density. A few candidates gave
answers which were incorrect in terms of significant figures.
Q.2
Q.3
(b)
(i)&(ii) Candidates who had successfully calculated the absolute uncertainty
in (a)(i) had little trouble in determining the three possible materials
required. ‘Error Carried Forward’ (ecf) was applied from (a)(ii). A
significant number of candidates who successfully identified the
correct materials gave vague and ambiguous reasons for their choices
however and were not awarded the second mark in (i). For example,
responses such as ‘because the uncertainty is large’ were not
credited. Nearly all candidates were successful in identifying volume
as the value which contributed most to the uncertainty in density. The
majority gave correct explanations for their answer in terms of
percentage uncertainty.
(a)
The majority of candidates were able to state the difference between baryons
and mesons in terms of quark make-up. Only a very small minority of
candidates described mesons incorrectly as two quarks.
(b)
(i),(ii)&(iii)
(c)
The majority of candidates were successful in identifying the correct force
involved in the interaction and nearly all of these also made correct reference
to photon involvement as one of the reasons for their answer. Fewer
candidates were able to give a second acceptable reason, either in terms of a
further reason for the force being electromagnetic (i.e. lifetime corresponds to
em force decay), or reasons why the decay could not involve a different force
(e.g. no lepton involvement, so not weak force).
(a)
(i)
The majority of candidates were successful in confirming Wien’s
displacement law through either confirming the Wien constant or the
star temperatures or the peak wavelengths of spectral intensity for
both stars. A small number of candidates were deducted one mark for
making ‘power of 10’ slips when taking wavelength readings from the
graph.
(ii)
Nearly all candidates identified Sirius A as being the ‘bluer’ star.
However, only a few were able to give correct explanations in terms of
the relative intensity of both stars at the blue end of the spectrum. In
many cases candidates merely made reference to the peak
wavelength of Sirius ‘being closer’ to the blue end of the spectrum,
which was not credited. Reference to temperature and its relationship
to colour did not address the question and no credit was given.
Nearly all candidates were able to give a correct quark makeup for the 0 meson. In (ii), candidates were expected to use
the conservation of baryon number and the conservation of
charge to show that the unknown particle was a proton (or ∆+).
A quark based analysis was accepted as an alternative to
baryon analysis. However, candidates who applied the
conservation of baryon number and also provided a quark
based analysis, with no reference to charge conservation were
only able to gain a maximum of 2 marks. Nearly all candidates
were able to show that lepton number was 0 on both sides of
the interaction.
© WJEC CBAC Ltd.
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(b)
Q.4
Q.5
(i)
The majority of candidates were able to apply the appropriate
equation relating luminosity and temperature correctly to successfully
show that the luminosity of Canopus is approximately 500 times the
luminosity of Sirius A. A significant minority however misinterpreted
the meaning of A and calculated either the cross-sectional area of
both stars or, in some cases, their volumes.
(ii)
A disappointing response in general. Few candidates were able to
calculate the intensity of the radiation reaching Earth from Sirius A.
Many candidates were unable to determine the surface area correctly.
(iii)
Nearly all candidates stated correctly that Canopus is further from the
Earth than Sirius A. Few, however, were able to provide an acceptable
explanation of the apparent contradiction in terms of the inverse
distance squared law. In a significant number of cases candidates
made reference to intensity decreasing with distance. This was not
credited.
The question tested candidates’ knowledge of the experiment to determine the
Young modulus of a metal in the form of a wire. Whilst it is understood that
candidates may have experienced other experimental techniques to determine the
Young modulus of a metal wire, the information provided in the question was
sufficient to enable them to answer the questions set.
(a)
(i),(ii)&(iii)
Few candidates were able to recognise the fact that the test
and reference wires were made from the same material and
that, consequently, temperature change would have the same
effect on both. The majority of candidates made incorrect
reference to the common support. Many candidates were able
to explain the term ‘elastic limit’ in (ii). However, few were able
to explain how an experimenter would know whether or not the
elastic limit had been reached in terms of loading and
unloading. Nearly all candidates were able to explain correctly
why a long wire was used, and also why the diameter of the
wire was measured at several different places.
(b)
(i)&(ii) The majority of candidates were able to take appropriate information
from the graph, correctly calculate the cross-sectional area of the wire
and use the appropriate equation to determine the Young modulus of
the material to an appropriate number of significant figures. Common
mistakes included calculating ‘A’ incorrectly, taking incorrect readings
from the graph or providing a final answer to an inappropriate number
of significant figures. Nearly all candidates were able to calculate the
energy stored in the wire. In some cases, ecf was applied for slips in
‘powers of 10’.
(a)
The QER question tested candidates’ understanding of the law of
conservation of energy as applied to a rolling marble on a curved ramp.
Responses in general were very good. Most candidates commented on the
simple and continued conversion of energy from gravitational potential energy
to kinetic energy, and they were able to link the form of energy to the position
of the marble on the ramp. Many candidates also commented on the transfer
of energy to other forms such as heat (internal energy) and the reasons (e.g.
friction effects) for this transfer and the eventual final state and position of the
marble on the ramp. The better responses contained a sustained line of
reasoning which was coherent, relevant, logically structured and covered
nearly all of the relevant marking points. The weaker responses contained
just a few of the key marking points and were generally unstructured and
lacked coherence.
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(b)
Q.6
Q.7
(i)
Responses, in general, hinted strongly that candidates were aware of,
and understood the reason why the work done on the sled could not
have been calculated using the 280 N force. Responses from a
significant minority of candidates were vague, ambiguous or
incomplete however and did not warrant any credit. Responses such
as ‘not all the 280 N is used to pull the sled’ were often seen for
example.
(ii)
The majority of candidates were able to calculate the mean power
needed to pull the sled. In most cases the value for the work done on
the sled was determined and then used correctly to determine the
mean power. In a minority of cases, the sled’s velocity was
determined and used appropriately in P = Fv. A variety of appropriate
units were nearly always given for P.
(a)
Only a minority of candidates were able to distinguish between the horizontal
and vertical components of the velocity of the projectile. Those candidates
that were successful in describing the motion in both planes were unable to
explain their answers in terms of the forces acting/not acting on the projectile.
(b)
(i)
The majority of candidates calculated the horizontal velocity of the
lander correctly.
(ii)
Only a minority of candidates were successful in using an appropriate
equation of motion to find the acceleration due to gravity on the comet.
In many cases candidates incorrectly substituted the value of the
horizontal component (found in (i)) into their chosen equation(s).
(iii)
A well answered question. Even those candidates who failed in
part (ii) used the given value for g to successfully show that the
vertical velocity of the lander after the first bounce was greater than
60% of the given escape velocity.
(c)
The majority of candidates were able to give three valid and convincing
arguments for or against the space mission by expanding on the bullet points
given. For example, on noting that 2 000 people were involved in the
development of the spacecraft, many candidates recognised the positive
impact this would have on job creation. Other common responses recognised
the positive impact that advanced solar cell technology would have on
developing renewable energy sources. Comments which did not expand on
the bullet points were not credited.
(a)
Nearly all candidates were able to define a vector.
(b)
(i)
The majority of candidates were successful in showing that the total
momentum before the collision was the same as the total momentum
after the collision. Alternatively, a small minority of candidates showed
that the loss in momentum of wagon A was equivalent to the gain in
momentum of wagon B. A noticeable number of candidates misread
the momentum axis and were penalised one mark for a ‘power of 10’
slip.
(ii)
The majority of candidates were able to apply the law of conservation
of momentum to determine the final velocity of both wagons correctly.
© WJEC CBAC Ltd.
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(c)
(i)
Only a minority of candidates stated Newton’s second law in terms of
momentum as required. The majority of responses were based on
ΣF = ma, either in equation form or in words. Whilst this is recognised
as a correct form of the law, this approach did not answer the question
as stated and no credit was subsequently awarded. Credit was
awarded however for the ‘rate of change of momentum’ formulae with
all terms being defined. The question was deliberately asked in this
form in the hope that it would provide some guidance for candidates
when attempting parts (ii) and (iii).
(ii)
The majority of candidates who were able to provide correct answers
to part (i) were successful in taking the appropriate information from
the graph to determine the resultant force on wagon A.
(iii)
Nearly all candidates correctly identified Newton’s third law, however
few candidates were able to use the information provided to fully
explain their answers.
© WJEC CBAC Ltd.
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PHYSICS
General Certificate of Education
Summer 2016
Advanced Subsidiary/Advanced
UNIT 2 – ELECTRICITY AND LIGHT
The mean performance was fairly even across the three main topic areas: waves (questions
3, 4, 6), photons (1 and 2) and electricity (5 and 7).
The mean mark would have been significantly higher if three question parts hadn’t scored badly.
Question 2(b) was designed to be an undemanding test of the new items, (m) and (n), in
section 7 (photons) of the specification. Question 4(a) asked for the derivation of the diffraction
grating equation (another addition to the specification). Question 6(a) was set as a
straightforward test of stationary wave theory in a familiar context. More information is given in
the detailed report below.
As usual mathematical questions were generally done better than those requiring words, though
a pleasing number of candidates rose successfully to the challenge of the QER question
(7 (b)(ii)) and the ‘issues’ question (7(c)).
Q.1
Q.2
(a)
(i)
Most candidates found the emitted wavelength correctly. Common
mistakes were to omit or bungle the conversion from eV to J and to use
level U’s energy as the photon energy.
(ii)
There were many very good accounts of how stimulated emission
produces amplification, including the wavelength (or energy or
frequency) requirement for the stimulating photon and some
information about the emitted photon. A misconception, perhaps seen
less often than in the past, was that the incident photon raises the
electron from L to U and two photons are emitted when the electron
drops back. A significant number of answers had electrons thoroughly
confused with photons, or in other ways revealed a very poor
understanding.
(b)
Many candidates gained a mark by stating that the four-level system required
less pumping, or produced a population inversion more easily, than a three
level system. The second mark, not gained quite as often, was for saying why
this is so: level L is self-emptying or words to that effect.
(a)
(i)
Most definitions of the work function were correct.
(ii)
I.
The effect and non-effect of increasing intensity on emission rate
and Ek max were well explained by many, though there were also
some very confused answers, some of which associated light
intensity (at fixed frequency) with photon energy.
II. A very pleasing proportion of candidates used a clear and correct
strategy to determine whether light of 5.1  1014 Hz would eject
electrons. They first found  for potassium from the data in the
question stem. Negative values for Ek max for the 5.1  1014 Hz light
weren’t accepted as a conclusion without a statement that there would
be no emission.
© WJEC CBAC Ltd.
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(b)
Q.3
(a)
(b)
(i)
Many candidates gained a mark for giving the photon energy in the
hc
form
, but, disappointingly, far fewer divided this into the beam

power, P, to get N, the number of photons per second. Both marks
P
were given for N 
. When, in the past, virtually the same
hc
( )

question has been asked with numerical data supplied, candidates
have fared better – despite the extra effort needed to produce a
numerical answer.
(ii)
The first mark was given for stating or implying that the change in
h
photon momentum per second was N  ( ). The second was for

P
substituting the expression for N from (i) and simplifying (to
but
c
with ecf on N). Most candidates failed to gain the first mark even if
h
they had obtained
from the data booklet.

(iii)
The quantity to be calculated in (b)(ii) was often, but by no means
always, identified as a force.
(i)
Given the angles to the normal of a ray entering a transparent
medium from air, a majority of candidates correctly calculated the
speed of light in the plastic. Those who couldn’t often gained a mark
for calculating the refractive index.
(ii)
Most went on to calculate the critical angle correctly.
(i)
Most candidates realised that the greatest angle to the axis for
successful transmission implied that the angle of incidence was the
critical angle, and found nclad from the equation:
ncore sin 81° = nclad [sin 90°]
A common mistake, costing one mark, was to use 9° rather than 81°.
An angle other than 90° on the cladding side of the equation
destroyed the logic, losing both marks.
(ii)
To “show that...”, candidates needed simply to write
1
1
cos9o
or
. Many did, though weaker candidates didn’t see that a trig
sin 81o
ratio was needed.
(iii)
Determining whether 150 m of fibre would cause a delay of more than
7.5 ns needed some planning. A pleasing proportion of candidates
rose to the challenge. Most found the difference in the times taken for
light to travel through 150 m of fibre, along the axis, and via the zigzag
route. The commonest mistake was to forget that the speed of light in
a vacuum needed to be divided by n for the core. At least 1 mark was
usually scored.
© WJEC CBAC Ltd.
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Q.4
Q.5
(a)
Derivation of the diffraction grating equation is a new arrival in the
specification. Few candidates drew and labelled the right-angled triangle on
which the derivation hinges. It only remained to identify the side of length d
sin as the path difference for light going to a distant point from adjacent slits,
and to point out that d sin = n was therefore the condition for light to ‘arrive’
in phase. These easy marks were usually forfeited.
(b)
(i)
Disappointingly, only about half the candidates drew good graphs of
sin against n, from the values of  and n supplied. Sometimes poor
scales were chosen or axes left unlabelled, but a surprisingly common
mistake was to plot  rather than sin
(ii)
Using the graph, and the value given for d, to determine  was well
done by about half the candidates. Surprisingly few found the graph

gradient and equated it to , but full marks were available for
d
methods using a point from the graph line.
(a)
Definitions of potential difference were usually good, with most candidates
remembering to include ‘per unit charge’.
(b)
(i)
Wrong answers for the open circuit voltmeter reading were rare.
(ii)
There was a high success rate in determining the internal resistance.
A two stage calculation was favoured, most candidates finding the
current as a first step.
(iii)
Most candidates wisely based their answers on time =
(iv)
Determining the new closed-circuit voltmeter reading when the
1.50  resistor was replaced by 0.75  was generally poorly done. A
very common wrong answer was 0.92 A  0.75  = 0.69 V, that is
retaining the same current as before, rather than the same internal
resistance.
(i)
Calculating the voltmeter reading for the potential divider was usually
done well, but weaker candidates sometimes failed to match pds to
the right resistances – a difficulty that probably goes back almost to
the days of Georg Simon Ohm.
(ii)
Asked to explain in clear steps what would happen to the voltmeter
reading when the light intensity was increased, candidates quite often
told us that “the LDR’s resistance will decrease so the voltmeter
reading will go up”. This didn’t count as an explanation, since the
LDR’s behaviour was given in the question. On the other hand, saying
that the total circuit resistance decreases was rewarded as a useful
step forward; the argument could be completed by pointing out that
the current would then increase and so also the pd across the 100 .
Good arguments were sometimes given using potential divider theory.
As a general rule, an acceptable answer had to include some
reference to the 100  resistor! Many answers didn’t.
(c)
energy
.
power
Unsurprisingly, many didn’t realise that the total energy dissipation
called for the corresponding power to be emf  current, not
terminal pd  current. This mistake cost 1 mark.
© WJEC CBAC Ltd.
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Q.6
(a)
(b)
Q.7
(a)
(b)
(i)
Interference-based explanations of antinode formation between the
microwave source and the metal plate ranged from very good to
unexpectedly poor. It is suspected that, despite the classic set-up and
the listing of antinodes at regular intervals, many candidates didn’t
realise they were dealing with stationary waves.
(ii)
It was hoped that candidates would argue that  must be 32 mm,
because the distance between antinodes was 16 mm, and that since

P was 8 mm, that is , from an antinode, it must be a node. Such
4
answers were not common, though 1 mark was often given for
arguments based on the node-antinode (N - A) distance being half
the A - A distance.
(i)
Most candidates realised that oscillations at A and B were in
antiphase. “Exactly out of phase”, “half a cycle out of phase”, 180° out
of phase or “ out of phase” were all accepted, but the occasionally
seen “half a wavelength out of phase” was not. Most candidates
realised that the longest wavelength consistent with this phase
relationship was 0.60 m, but the second longest wavelength (0.20 m)
was, not surprisingly, more elusive.
(ii)
To determine which of the two wavelengths was consistent with the
given range of wave speeds needed some plan of action, and it was
good to see many well-argued answers. Even those who didn’t score
3 marks usually gained 1 for calculating the frequency correctly.
(i)
Most candidates drew a usable circuit for obtaining V and I readings
for a filament lamp. Many, though, did not. Mistakes ranged from
having no way of varying V, or omitting one of the meters, to shortcircuiting the lamp by putting an ammeter across it, or preventing
current flow by having a voltmeter connected in series.
(ii)
Most candidates selected the better current range (0 – 200 mA),
though they didn’t always justify their choice, for example by pointing
out the likelihood of better resolution.
(iii)
Many pointed out that more pairs of readings were needed, so that
more points could be plotted (especially from 0 to 1.5 V), and that
points were needed between 2.25 V and 3.0 V. More even spacing of
points was sometimes offered; this wouldn’t necessarily be an
improvement.
(i)
Except for the occasional minor error, candidates read the graph
correctly and went on to calculate the resistances and their ratio
successfully.
(ii)
Candidates were asked for free electron explanations of why the
temperature and the resistance of a metal wire increased when the pd
across it is increased. Most realised that the key idea was (free)
electrons colliding with ions (we accepted atoms, particles, or lattice).
Many correctly wrote of the ions vibrating, and receiving extra energy
from electrons during collisions. The link between increased (random)
energy and temperature was usually appreciated, though there was a
tendency to claim that the vibrating ions ‘gave off heat’ and that the
heat caused the temperature to rise. This confusion was not penalised
specifically. Many candidates understood that the wire’s resistance
© WJEC CBAC Ltd.
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was due to electron-ion collisions, but the point that the increase in
resistance was due to the increase in (amplitude of) ionic vibration
wasn’t made very often. [Other misconceptions noted were that free
electrons are vibrating, and that the link between increased resistance
and increased temperature was somehow independent of all the stuff
about ions and free electrons.] Nonetheless, a fair number of
candidates made it into the top band (5 or 6 marks out of 6).
(c)
As we had hoped, most candidates used their knowledge about
superconductors to justify continuing the research, in terms of energysaving. The special advantage of superconductivity at room
temperature – no cooling complexities or cost – was pointed out less
often. As an argument for not pursuing the research, a little more than
“If it doesn’t work, it’s a waste of money” was needed. Emphasising
the apparent unreproducibility of the results was enough.
WJEC GCE New AS Physics Report Summer 2016
© WJEC CBAC Ltd.
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