(PDF) GCE January 2004 Report on the Examination - … 12,13/A level Physics past papers... · Report on the Examination ... examiners expected a certain amount of unit errors to be incurred - PDFSLIDE.NET (2023)

GCE 2004

January Series

Report on the Examination

Advanced Subsidiary 5451Advanced - 6451

GCE PhysicsSpecification A

Advanced Subsidiary

Advanced

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CONTENTS

AS Units

Page No.

PA01......................................................................................................4

PA02......................................................................................................6

PHA3/P.................................................................................................8

PHA3/C..............................................................................................12

PHA3/W............................................................................................14

A2 Units

Page No.

PAO4 Section A..............................................................................16

PA04 SectionB...............................................................................19

PHAP Units 5-9 Practical............................................................ 21

PHAC Units 5-9Coursework......................................................25

PHA5/W PHA9/W SectionA................................................... 25

PHA5/W............................................................................................26

PHA6/W............................................................................................28

PHA7/W............................................................................................30

PHA8/W............................................................................................31

PHA9/W............................................................................................32

PA10...................................................................................................34

Mark Ranges and Award of Grades......................................................................37

Physics A - Advanced Report on the Examination

4

Physics

Specification A

Advanced Subsidiary Examination

The January 2004 examination saw a significant increase in thenumber of candidates enteredfor the PA01 and PA02 examinationscompared with the January 2003 entry. Unit 1population increased byalmost 22% and unit 2 by 24%. This increased number ofcandidates,some of whom may have transferred forward from previous Juneentries, may bea consequence of the changes made to the lengths ofthe papers and the consecutive schedulefor AS. Such a largeincrease could significantly affect the ability profile of theJanuarycohort. The entry for the third written paper, PHA3/W,stayed reasonably the same.

The examiners were well pleased with the response to all theexaminations and there was no

evidence to suggest that any particular topic in theSpecification had not been taught. With

such large entries, examiners expected a certain amount of uniterrors to be incurred.

Similarly with significant figure errors. The Quality of WrittenCommunication appears to

have improved over the years. Candidates do seem to be awarethat the maximum marks

available for QWC constitute 4% of the total marks for the paperand consequently take

greater care when answering the sections designated for QWC.

Unit 1: PA01: Particles, Radiation and Quantum Phenomena

General Comments

The paper was well received by the candidates and only theweakest failed to attempt allquestions. All marking points wereawarded and some scripts scored full marks. The paperenabled weakercandidates to make some attempt at most questions and allowed themoreable to gain 80% or more of the marks. It thus discriminatedwell and at the same time gavecandidates a positive feeling ofsuccess and ability to answer questions.

Question 1

A minority of candidates failed to score the two marks in part(a) because they interpretednucleons as neutrons. Part (b)presented more of a challenge for the more able candidatebecausethe fractional charge and the fractional baryon number for quarkswere concepts thatwere not universally understood. Many candidatestook this part of the question to mean,Are the quantities conservedor not? The other common error was failing to assign correctleptonnumbers. Because of these difficulties the question turned out tobe a gooddiscriminator between candidates.

Report on the Examination Advanced - Physics A

5

In part (c) the majority of candidates were aware that thepositron and the electron suffered

annihilation but only the better candidates referred to theproduction of two photons. Anoticeable number of the less ablecandidates confused annihilation with pair production.

Question 2

The average candidate performed well on this question. Manycandidates lost marks by

describing the meson as having two quarks rather than having aquark plus an antiquark.

Other candidates lost marks because of the ambiguous way inwhich antiquarks were

included in their description of a baryon.

In part (b) many of the weaker candidates were under theillusion that a lepton had a quarkstructure and also that thechange to the quark structure during the decay was a change toanantiquark rather than a down quark changing to an up quark.

Question 3

As in previous years only a minority of candidates completed theray diagram correctly, thus

gaining full marks. The first error in part (a) occurred at thepoint where the ray entered the

fibre; many candidates drew the refracted ray along the normal.There was a general lack of

care in not making the angle of incidence different in value tothe angle of reflection.

Additionally, many candidates did not show any refraction at thefar end of the fibre. Some

of the TIR angles along the fibre were very carelessly drawn andthe allocated mark was

withheld on several occasions. Although most candidates wereaware of the change in the

speed of light as the ray entered the fibre, many failed tostate that there was also a change in

speed as the ray left the fibre.

The calculation in part (b) (i) was usually carried outcorrectly, but in part (ii) the less able

candidates did not attempt to use both refractive indices. Manyof the statements made in

answer to part (iii) were of a very general nature and did notexplicitly refer to surface

scratches or contamination.

Question 4

Part (a) caused problems for a significant number of candidates.It was common to find the

frequency of the incident radiation being calculated and thenthe value substituted back into

the photoelectric equation in order to calculate the energy. Theunit of work function was

often incorrect, resulting in a lost mark.

Part (b) discriminated very well, even in the top ability range.For those candidates who

failed on this part, some of the more common errors were: takingthe energy to be

proportional to the wavelength, doubling the value of the workfunction instead of doubling

the incident energy of each photon and basing the energy of thephoton on the photoelectron

energy.

Physics A - Advanced Report on the Examination

6

Question 5

The explanation of the excitation process in part (a)(i) wasdone well. There were very few

references to ionisation, which has occurred in previous papers,and also practically no

candidates referred to an electron leaving a metal. There was atendency to continue the

explanation into the relaxation process, which was unnecessary.In part (ii) several

candidates worked backwards to the expected answer. Thesecandidates typically wrote that

the wavelength was fixed because the frequency was fixed becausethe energy was fixed. It

was easy for these candidates to miss the relevant markingpoints. Very few candidates gave

clear statements about the energy levels occurring at discreteenergies or that an electron

drops down an energy level when a photon was emitted.

Part (b) again proved to be a good discriminator. In part (i)several candidates attempted to

use the de Broglie relationship instead of the usual = ch/E. Inparts (ii) and (iii) only about

half the candidates gave the correct transition and the correctdirection. Most of them

successfully converted the energy of the transition from joulesinto eV.

Question 6

Too much time was spent by candidates repeating the wording ofthe question and explaining

the wave particle duality. There was also a tendency toconcentrate on one or two pieces of

evidence, thereby excluding themselves from gaining full marksbecause of the lack of

coverage. It was this aspect of the submitted answers thatreally governed the marks awarded,

rather than candidates making errors. It was also clear thatmany candidates thought it only

necessary to discuss the wave view of an electron and theparticle view of an electromagnetic

wave.

Unit 2: PA02: Mechanics and Molecular Theory

General Comments

The performance of candidates in this unit was generally goodwith none of the questionsproving inaccessible. The structure ofthe questions helped to improve accessibility for theweakercandidates. Overall the candidates performed better than in January2003 and severalwere awarded full marks. It was also felt by theexaminers that this years questions, with alower total, lacked someof the more difficult sections seen in earlier papers.Candidatesfound questions 2 and 3 the most difficult and this wastrue for all ability levels. Presentationwas generally satisfactoryand candidates set out their calculations so that there was alogicalstructure to the answers. Significant figure errors werecommon in question 3 and unit errorscommon in question 2. TheQuality of Written Communication was good and it was notunusual tofind weak candidates being awarded full marks for this skill.

Question 1

This question was done well with most candidates in part (a)successfully explaining the

meaning of a scalar quantity and able to give suitable examples.Calculating the third force

and the angle in part (b) did not present too many problems andcandidates across the ability

range approached this task with confidence. A few candidates didopt for a scale drawing but

they were very much in the minority.

Report on the Examination Advanced - Physics A

7

Question 2

The question, as a whole, proved to be a good discriminator. Thevarious calculations in part

(a) were quite demanding for a significant proportion of thecandidates and unit errors were

quite common for all the quantities involved, including thosefor the more straightforward

quantities such as acceleration and speed.

Candidates were asked to sketch two graphs in part (b). Thisproved to be quite a difficult

exercise with the non-linear, distance vs. time, graph being themost difficult to draw

correctly.

Part (c) produced the same problems that questions of this typehave produced in previous

papers. Many candidates insisted on using Newtons third lawincorrectly and consequently

getting into real trouble. Statements such as the air resistanceis the reaction to the driving

force action were common and were awarded zero marks.

Question 3

Again candidates found this a demanding question and asignificant minority were not even

able to convert the temperature from Celsius to Kelvin in part(a). In the same section, the

calculation of number of moles of gas and the number of gasmolecules also proved difficult

and significant figure errors were common.

Part (b) realised better answers, although many candidates didnot seem to appreciate that

temperature is related to the mean kinetic energy and not to thekinetic energy of an

individual molecule.

Question 4

This question, based on the principle of moments, differed fromprevious questions on this

topic, in that a descriptive question on moments had not beenpreviously set. Candidates

generally rose to the challenge and approached the descriptionof the experiment in parts (b)

and (c) with confidence. The procedural descriptions did tend tolack clarity but candidates

were generally able to score reasonable marks. A minority ofcandidates totally

misunderstood the question and described experiments whichverified the conservation of

momentum.

Question 5

The last question in the paper was generally done well andcandidates across the ability range

were able to perform the various calculations successfully. Aminority were confused by the

need to use only 60% of the kinetic energy, but because markswere awarded for

consequential errors, this did not prove to be too much of apenalty.

Physics A - Advanced Report on the Examination

8

Unit 3: PHA3/P: Practical

General Comments

Although the entry for January 2004 had increased by about 10%over the January 2003

entry, the statistical distribution of marks for the twoexaminations was strikingly similar.

Candidates seemed to find question 1 slightly easier andquestion 2 slightly harder than

previously, but the two effects cancelled to produce the samemean mark.

Within both questions all assessment objectives discriminatedwell, with every mark in the

range for AO3a (Planning) and for AO3d (Evaluating) beingutilised in the distribution.

Candidates who demonstrated A-grade ability could generallyexpect to gain 7 or 8 marks

(out of 8) for AO3a and at least 6 (out of 8) for each of AO3b(Implementing) and AO3c

(Analysing). Although they generally did better in AO3d thanother candidates, there was

more variation in their scores and it was this assessmentobjective that provided the best

discrimination among this group.

Candidates who might be expected to achieve a grade B or Cscored comparatively well in

AO3b and AO3c although slightly below the level achieved by thestronger candidates. They

usually achieved at least half marks in AO3a but often less thanhalf marks in AO3d. It was

their weaker performance in these assessment objectives thatprovided the most marked

distinction between the work of this grade of ability and thatof the best candidates.

Candidates who appeared to be of grade D standard and belowperformed less well in all

assessment objectives but particularly so in AO3a and AO3d,where many gained no mark in

either or both objectives.

The presentation of scripts was generally good and oftenincluded detailed sketches thatclarified issues that were leftunresolved in the written part of the answer, but the tabulationofdata was an area where the presentation of work could varyconsiderably. Graphical workwas frequently undermined by theobsessive need to include an origin or by the use of scalesthatmade interpretation difficult.

Although most candidates found the questions quite accessible,it is puzzling how often the

attempts at question 2 seemed laboured, with careless orinaccurate work from the outset. In

this question most candidates chose to determine y withoutmaking full use of the massessupplied and the majority werereluctant to utilise more than half the length of the suspended

ruler for their values of x.

Of the relatively few candidates who provided a satisfactorygraph only a very small number

were able to combine the gradient result with that of theinitial measurements to obtain an

answer for which full credit could be given. There waswidespread reluctance to give the

answer to the evaluation of G

y to more that 2 significant figures and suitable units were

hardly ever provided.

Report on the Examination Advanced - Physics A

9

Answers to question 1 tended to be over-long and often containedrepetitive, generalised

comments that could attract little or no credit. Simple, conciseanswers were sufficient in

many instances for full credit to be given, with many candidatesshowing a clear

understanding of the physical principles of the situation. Thetime may be approaching when

candidates will have to be restricted, for their own good, inthe amount they can be allowed to

write.

Candidates appeared to have ample time to complete theexamination.

Question 1

Candidates were required to describe a method of investigatingwhether a quantitative link

existed between the diameter of a hydraulic jump, produced aswater falls on to a horizontal

plate, and the flow rate of the water incident on the plate.

The question proved very accessible to the candidates, most ofwhom showed a reasonable

understanding of the problem. Very few failed to identify thatthe volume of water collected

in a fixed time (or the time taken to collect a fixed volume)would enable the flow rate to be

determined. However, a few candidates suggested impracticalideas where the speed, height

and cross sectional area of the water stream would bedetermined.

Most candidates specified a suitable method of finding thediameter of the jump (those who

said they would measure the radius were not penalised) and alarge number appreciated the

need to measure the diameter of the jump without interferingwith the flow. Suggestions as

to how this would be done included the use of transparent plateswith rulers below or the use

of callipers and dividers to pinpoint the diameter. Use of astopclock was almost universally

given credit, except where this was used to find the transittime of the water between the tap

and the plate.

The majority of candidates stated that in order to determine theflow rate they would measure

the volume of water (using a measuring cylinder) for a certaintime. The use of standard

containers to collect a fixed volume of water was also allowed,providing some idea was

conveyed as to how the volume of the water contained was known.Some suggestions for

finding the flow rate were impractical, with impossibly smallvolumes or short intervals of

time to collect it being suggested. A few candidates proposedcalibrating the tap and

introducing some rotary scale against which the position of thetap could be judged. Others

proposed some type of flow meter linked to a computer, aproposal that was given no credit.

A number of candidates suggested that the time taken for agraduated container (such as a

burette) to empty should be found; full credit could not begiven in such cases since the

candidate had failed to appreciate that this could not provide auniform flow rate. Others

proposed to carry out the investigation with water falling intoa tray or container from which

water could not naturally drain. Once again, full credit was notgiven, as the ensuing

flooding of the plate would affect the size of the jumpformed.

Most candidates clearly showed that they intended to vary theflow rate and measure further

jump diameters, and provided that the procedure they hadoutlined to find the flow rate would

work, credit was given. Many went on to suggest that a graphshould be drawn, but for credit

to be given, some attempt had to be made to explain how thiscould reveal whether a

quantitative relationship between jump diameter and flow rateexisted.

Physics A - Advanced Report on the Examination

10

The bulk of marks awarded were for describing how themeasurements were made (4 marks)

and for devising a suitable strategy to satisfy the setobjective (3 marks) but some candidates

also gained credit for identifying that the distance between thetap and the plate should be

maintained constant.

Marks for suggesting suitable procedures and identifying thedifficulty that these overcame

were hard to earn. As is often the case, many candidatesprovided a procedure but failed to

give the associated difficulty and bland statements aboutrepeating and averaging readings to

reduce uncertainty could seldom earn credit.

Some of the better procedures seen were repeating the diametermeasurement in different

directions, thereby compensating the possibility that the jumpwas not perfectly circular; to

wait for the shape of the jump to stabilise before takingmeasurements and to collect the

water over a long period or collect a large volume to reduceuncertainty in the flow rate.

Question 2

Candidates were required to investigate the equilibrium of aloaded metre ruler suspended

from a horizontal beam, by a combination of a wire of variablelength and four

interconnected springs.

Candidates found this to be a more accessible problem than thatset in January 2003, with

straightforward processing of the data and opportunities fromthe outset to limit the impact of

experimental errors on the evaluation of y

G

. Judging from the distribution of points on the

graphs seen, the majority of candidates carried out theexperiment without difficulty and the

answers given in part (e) (AO3d) confirmed that most werecapable of arranging the

suspended beam as required and measuring y reliably.

Where careful measurements were made in part (a), it waspossible to check that the values of

y were reliable but some candidates chose not to determine thevalue in a way that allowedthem to check for random error. Fullcredit was given less often than expected, mainly

because candidates had failed to measure 2y or 3y in order toobtain their answer. Otherslost marks because they failed to givethe reading to the nearest millimetre, as expected.

In part (b) both marks were generally awarded for tabulation,but it was common to withhold

one mark for the results because candidates seldom madesufficient use of the scope available

for measurements of x. Candidates were required to utilise atleast 50 cm of the available

range, but a surprising number used considerably less distance.Consistent use of significant

figures was generally widespread and most earned the relevantmark. The straightforward

nature of the exercise dictated that for the quality mark to beawarded, all five points should

fall within 2 mm on a suitably scaled graph; this often provideda useful discriminator in

favour of those who had used a wide range of x values.

Graphical work continues to be undermined by poor orinappropriate scaling. The inclusion

of the origin compresses the vertical scale, but there weresignificant numbers who chose

inconvenient scales simply to extend the distribution of points:this should be discouraged as

it makes plotting difficult and the determination of thegradient unreliable.

Axes were usually well marked but there were some instances ofwrongly or inappropriately

marked points.

Report on the Examination Advanced - Physics A

11

Gradient calculations were usually made with sufficiently largey and x steps, except where

compressed graph scales had made the line too shallow. It was amajor disappointment to

find how few candidates gained credit for their answers to theevaluation of y

G

. In some

cases the fault lay with the value determined for y in part (a),but in general the loss ofmarks was due to the lack of a unitand/or the contraction of the result to 2 significant figures.

Even the better candidates lost up to three of the six marksavailable in part (e) (AO3d), while

the weakest candidates generally scored only one or two marks.In part (e)(i) the required

answer was that the value of y was checked at each end of theapparatus; the suspended ruler

could be presumed to be horizontal when these two readingsmatched. Many candidates

stated precisely this. Others chose to measure up from the floor(or from the bench) to each

end of the suspended ruler and check that these readingsmatched, but in such cases they had

to state that the ruler used to make the measurement wasvertical. Any explanation which

involved a setsquare to compare the suspended ruler with thesuspension wires was not given

credit.

The majority of candidates understood that the verticalintercept on the graph would give the

value of y if the 300 g mass was removed from the suspendedruler, but few explained that

this was so because when placed directly below the wire (i.e. x= 0), the mass would exert no

turning moment and so be effectively removed.

Most candidates correctly deduced that if the experiment wasrepeated using a 200 g mass,

the gradient of the graph would be reduced. However, most arguedthat this would be due to

larger x values, which may be true, but is also ambiguous(larger x values can only lead to a

reduced gradient if the values are proportionally larger asopposed to being incrementally

larger). If candidates explained that x values would beincreased to produce the same turning

moment (given the reduction in the force applied to the beam)then full credit was given.

Physics A - Advanced Report on the Examination

12

Unit 3: PHA3/C: Coursework

A significant proportion of the candidates entered for thismodule were carrying forward

marks from the Summer 2003 examination. The comments in thisreport are therefore based

on new work submitted from a relatively small number ofcentres.

Most Centres completed the administration procedures correctlyand copies of Centre

Marksheets and samples of candidates work reached moderators bythe prescribed deadline.

In a few cases however, there was some confusion as to whichcopies of the Centre

Marksheet should be sent to the moderator. In small centres ofless than 20 candidates, just

the pink copy should be sent, together with the candidates workand the yellow copy retained

by the Centre. For larger Centres, both pink and yellow copiesof the Centre Marksheet

should be sent to the moderator. The yellow copy will bereturned, specifying the samples to

be sent to the moderator.

Overall, the quality of annotation was good, with only a fewCentres failing to adequately

annotate the work submitted. It should be noted that everymarking point must be annotated

at the precise point where the mark was awarded. The annotationshould be written in the

format A4b, B6a etc. referring to the appropriate marking point.Written comments are

also helpful, particularly in clarifying why a particularmarginal point has been awarded.

The use of a suitable marking grid to record the individualmarking points is also strongly

recommended. This makes it much easier to interpret thehierarchical scheme and determine

the total mark for each skill.

As in previous years a significant number of adjustments weremade to marks submitted by

centres. Almost all Centres applied the hierarchical schemecorrectly. Mark adjustments were

mainly due to misinterpretation of specific points in theassessment criteria; these are

explained in more detail below. Due to the hierarchical natureof the scheme however, one

error in interpretation of the criteria can cause a significantadjustment to the overall mark,

e.g. a candidate who, in the opinion of the moderator, hasfailed to achieve A4c (fully

labelled diagram), will be limited to a maximum mark of 3 forplanning. If this mark had

been awarded by the centre this might result in a mark changefrom 8 to 3.

In most cases the investigations used were appropriate, allowingtheir candidates access to the

full range of assessment criteria. Experiments on measurement ofresistivity and emf/internal

resistance were again very popular and successful in allowing afull range of marks to be

achieved by candidates. A small number of centres presentedinvestigations which did not

allow their candidates access to all the marking criteria. Thiswas usually because the

experiment did not generate a suitable graph from whichgradients and intercepts could be

calculated, e.g. investigations involving solar cells.

As in previous examinations a small proportion of candidatesmade use of ICT. Whilst

appropriate use of ICT is to be encouraged as part ofinvestigative science, many candidates

were penalised due to graphs and results tables which did notmeet the assessment criteria.

Graphs drawn by ICT software must meet exactly the same criteriaas hand drawn graphs.

They should produce a graph, which covers a full side of A4paper with a suitable title and

fully labelled axes. Points should be plotted as points orcrosses and not shapes, such as large

squares or diamonds, which make precise location of the plottedpoint more difficult. The

line of best fit should be drawn taking account of any anomalouspoints. The graph should

Report on the Examination Advanced - Physics A

13

have suitable gridlines so that accurate readings for gradientsor intercepts can be recorded. A

suitably large triangle for measurement of gradient must also beshown.

The advice which follows addresses issues raised by moderatorson the marking of specific

skills. Many of these points were also discussed in the recentseries of Teachers Support

Meetings held last autumn.

In skill A there were still a few cases of candidates failing tomention a consideration of

safety issues, thereby effectively limiting their mark to amaximum of 1. To achieve A4c,

diagrams must be two dimensional, fully labelled and dimensionsbeing measured must be

clearly indicated. If the length of a string or wire is beingmeasured it should be drawn as a

straight line with the dimension indicated. A4c was the mostcommon point misinterpreted by

centres, and frequently caused a significant adjustment in themarks awarded. To achieve

A6d full instrument specification is required and for electricmeters this requires both range

and sensitivity. Occasionally unrealistic instrumentsensitivities were quoted, e.g. metre rules

reading to 0.05 mm.

In skill B, some candidates failed to take enough readings withappropriate repeats to achieve

B4c. In an experiment to investigate the variation of resistancewith the length of wire, it

would be expected that candidates do at least 7 or moredifferent lengths with repeat readings

for resistance at each length. Some centres awarded this markincorrectly where candidates

had only done 5 or 6 different readings.

Quoting results to an inappropriate number of significantfigures was the main cause for

concern in skill B. This usually occurred where a lengthmeasured to the nearest mm was

quoted only to the nearest cm, e.g. 0.20 m rather than 0.200 m,and often results in a mark

adjustment from 8 to 5 on this skill.

In B6d, candidates must clearly identify the significantsource(s) of error which occurred in

their experiment. Although in the planning stage they might havesuggested a particular error,

a further statement would be required after results have beentaken to confirm whether or not

this is still considered to be the most significant error.

In skill C, to achieve C4c an appropriate scale must be used sothat the plotted points occupy

more than half the length of each axis. If this makes itimpossible to read a particular

intercept directly, a suitable calculation should be doneinstead. Some centres awarded C4c

for graphs with no titles and where the plotted points occupiedless than a quarter of the area

of the paper. This caused significant adjustment to the marksawarded, effectively limiting

the mark for skill C to a maximum of 3.

In skill D the majority of candidates scored less than in theother skill areas. Many candidates

failed to achieve all four marking points in D2, effectivelylimiting their mark to a maximum

of 1 for this skill. In particular, for D2b a simple statementabout discrepancies or anomalous

results is required. For D2c, candidates must state whetherthere is much variation in their

repeated results, indicating the level of uncertainty in thedata. In D4b, candidates frequently

calculated errors based on instrument sensitivity only. Wherepossible the error estimate

should be based on the spread of repeated results, e.g. in anexperiment to investigate the

variation of resistance with length of wire, the error in lengthmight reasonably be based on

the accuracy of the rule (1mm). The error in resistance,however, should be taken from the

Physics A - Advanced Report on the Examination

14

spread of repeated readings, and not the sensitivity of themeters used. In D6a a large

proportion of candidates are unsure of the difference betweenrandom and systematic errors.

Unit 3: PHA3/W: Current Electricity and Elastic Properties ofSolids

General Comments

All questions on the paper worked satisfactorily and noparticular question proved to be too

difficult for the candidates. All marking points were awardedand maximum marks were

gained by a few candidates. Very few incorrect units werepresented, but the unit of

resistivity in question 2 did create some difficulty.Significant figure errors were few and far

between and seemed to occur at random throughout the paper. Itwas pleasing to note that

very few answers were presented in the form of fractions. TheQuality of Written

Communication was of a good standard. It does seem that extracare is taken when

candidates know which sections are being scrutinised.Unfortunately, this attention to quality

in certain sections did not manifest itself throughout the wholepaper.

Question 1

The question involved straightforward calculations on voltage,resistance and current. In part

(a)(i) it was hoped that candidates would have spotted thecorrect voltage across each lamp

by inspection. Surprisingly, even those who managed to get thewrong answer in part (i)

nevertheless ignored their answer and proceeded from firstprinciples to obtain the correct

answer to part (ii).

Part (b) involved the same circuit components as in part (a) butconnected differently. The

majority of candidates showed that the current from the batterywas the value given in the

question. Using this value they then proceeded to argue orcalculate the current in each lamp.

Those candidates who merely halved the current value obtained inpart (i) without any

reasoning did not gain the mark.

Although the question told the candidates that the currentthrough each lamp was the same in

both circuits it was disappointing to find in part (c) how manycandidates tried to argue that

the brightness of the bulbs in the 2nd circuit would bedifferent to that in the first, the main

thrust of their argument being that the voltage across each bulbwas different and therefore

that the brightness would be different.

Question 2

The large majority of candidates gained the two available marksin part (a) without much

difficulty and supported their choice of conductor with thecorrect argument.

Some care was required in part (b) in reading the graphaccurately and the fact that the

majority of candidates simply put down 0.7 A at a voltage of 1.0V, showed that they gave the

graph no more than a cursory glance. It should also be pointedout that drawing vertical and

horizontal lines in thick pencil or in ink on the graph veryoften obliterates the required point

and accurate values can then not be read. The explanation inpart (b)(ii) of why the resistance

increased was satisfactorily done in terms of the increasedtemperature of the filament,

although for a complete answer it should be pointed out that itis the current that heats up the

filament. Very often there was no direct reference to thetemperature of the filament, but

Report on the Examination Advanced - Physics A

15

instead a general phrase such as ...leads to an increase intemperature... or heat is

created....

The calculation on resistivity in part (c) was more often thannot carried out successfully.

The errors which did occur was taking the resistance as thegradient, and not as the inverse of

the gradient and omitting or using wrong units.

Some circuit diagrams in part (d) were very well drawn and themajority of candidates

obtained full marks. The usual omission was a variable resistoror variable supply to alter the

voltage. If a potentiometer is used then it is important to showthe ammeter in series with the

filament and not in series with the power supply. Somecandidates lost a mark by connecting

the voltage and current sensor directly to a computer ratherthan through the data logger.

Question 3

High marks were usually obtained in this question. Very fewcandidates failed to gain full

marks in part (a) although it was sad to see some giving thepeak voltage as Vrms/2.In part (b) a large number of candidateswere obviously familiar with the correct terminology

of the oscilloscope controls, but other terms were alsoaccepted. The calculations of the new

settings were generally well performed.

Question 4

Candidates found this question very accessible and many gainedfull marks. In part (a) the

meaning of emf seems to be reasonably well understood with mostcandidates opting for the

voltage when no current passed through the circuit. Othersdefined it correctly in terms of

energy per unit coulomb. There were, unfortunately, manycandidates who, apparently, had

not encountered the definition of emf and merely quotedelectromagnetic force, or even tried

to define it in terms of a force in the circuit. The calculationof the current in part (ii) was

well done and in part (iii) correct substitution of values intothe equation = V + Ir gave r =

0.80 .

Part (b) was involved with calculation of power and energy andalthough the majority of

candidates obtained the correct answer for the power dissipatedin the 2.4 resistor, fewerhad the correct answer for the totalpower dissipated in the circuit and a disappointing

number had the correct value for the energy wasted the battery.The usual answer to the last

part was to give the energy in the complete circuit. Whetherthis was due to inaccurate

reading of the question or due to lack of understanding couldnot be decided.

Question 5

In part (a) the definitions of tensile stress and tensile strainwere usually correct although

some candidates were penalised for not stating that the areainvolved was the cross-sectional

area. A definition of tensile stress as force per unit area wasnot accepted.

Part (b) gave candidates the opportunity to write at length onwhat they knew about stress-

strain curves. Most accounts started off well with the easilyrecognisable linear region

obeying Hookes law. A linear region given in terms of a constantYoung modulus was not

accepted. The point A on the graph was not always defined as thelimit of proportionality.

After this initial section the descriptions became more vague.There seems to be some

Physics A - Advanced Report on the Examination

16

confusion as to where the elastic limit occurs and this is nothelped by some textbooks. In

this question the examiners were prepared to accept that theelastic limit occurred from A to

the region B. A phrase which occurred regularly was plasticdeformation without any

attempt being made at explaining what it meant. It would havebeen worthwhile for the

candidates to extend their sentence by stating that the wire didnot regain its original length or

shape once the applied force was removed. Many candidatesthought that because the graph

became reasonably straight around section C that Hookes law wasobeyed again. The

impression gained by the examiners was that the topic was, onthe whole, loosely taught and

that candidates memorised terms such as elastic limit withoutfully realising what happened

to the wire.

Question 6

This is the first time since this Specification was introducedthat a question on density has

been set. The examiners were pleased to find that the majorityof candidates seemed to

understand the topic very well and gained full marks.Unfortunately, candidates who gave

density as = mass volume were, because of the nature of thequestion, penalised quiteheavily, but they could however earn marksfor calculating the volume in part (b)(i) and

adding the masses together in part (ii).

Advanced Examination

With the exception of paper PA04, the entry for A2 remainedsmall and thus it is difficult to

generalise on the standard achieved in the option papers andsynoptic papers. The entry for

PA04 remained at approximately 3000 (January examinations) andthe entry for the synoptic

paper, which is by now becoming well established, almost doubledfrom January 2003 to 80

candidates this year.

All the Principal examiners were satisfied that the papers hadbeen fair and all questions

accessible to the candidates.

Unit 4: PA04: Section A: Objective Test Questions

The keys to the objective test questions were:

1-C; 2-A; 3-D; 4-D; 5-B; 6-A; 7-C; 8-D; 9-C; 10-C; 11-A; 12-C;13-C; 14-B; 15-B.

General Comments

The facility of a question is a measure of all candidatesattempting a question who choose the

correct option. The mean facility of this paper was 70%,compared to 57% and 60%

respectively in January and June 2003. The facility forindividual questions ranged from

90% for question 14 to 52% for question 4.

Report on the Examination Advanced - Physics A

17

The point biserial index of a question is a measure of how wellthe question discriminates

between the most able and the least able candidates. The meanpoint biserial for this paper

was 0.45, slightly higher than the values of 0.41 and 0.44respectively in January and June

2003.

No fewer than ten of the questions (all except Questions 3, 4,9, 12 and 15) proved to be easy,

with facilities over 65%, whilst no question was found to bedifficult. Only one of the

questions had appeared in an earlier Advanced level examinationand in January 2004 the

candidates performance on this question was a noticeableimprovement over that on the

previous occasion. This contrasts with recent experience withre-banked questions in

previous PA04 papers, where present-day candidates havegenerally not been able to match

the performances of their predecessors.

Statistical analysis of the results has shown this test to berather more accessible than the

2003 papers, but also provided some evidence that the cohorttaking the paper was slightly

more able. Examiners marking Unit 4 Section B detected a similartrend in the candidates

abilities.

Question 1 amounted to a two-stage calculation on simpleharmonic motion. The facility of

84% was a significant advance on that of 67% in thepre-examination test.

Wrong responses were almost equally divided between distractorsA, B and D.

Question 2 was set in the context of a simple pendulumexperiment, requiring candidates to

show knowledge of how g could be found from the gradient of agraph of T2 against l. The

facility was 69%, a similar improvement over the pre-test toQuestion 1. Distractor B, chosen

by one in six, was the most popular incorrect response; this maysuggest that these candidates

had difficulty with algebraic re-arrangement.

Question 3 tested the graphical relationship between kineticenergy and displacement in

simple harmonic motion. The facility of 59% was an improvementover the 50% achieved

when this question was pre-tested. Almost one in five of thecandidates chose distractor A,

forgetting that there are two cycles of energy for every cycleof displacement

Candidates found Question 4, with a facility of 52%, to be themost demanding question on

this paper, but it was one of the best discriminators. Manycandidates have obvious difficulty

in appreciating the function of the defining slit in Youngsexperiment, because distractor A

was chosen by almost 20%. Distractor B was nearly as popular,perhaps because problems

with logic made it difficult to interpret what was meant by twodecreases.

Question 5 was not considered easy when it was set, because itinvolved rather more than a

straightforward answer achieved by direct substitution in n = dsin. Only 50% got the

correct answer when this question was pre-tested, but thisimproved to 67% in the

examination. No doubt the 17% who chose distractor C did sobecause they forgot to

subtract the angle with n = 2 from the angle with n = 3.

The geo-synchronous satellite in Question 6 did not seriouslytrouble many of the candidates,

since the facility was 80%. Wrong responses were almost evenlysplit between the remaining

three distractors, with none attracting more than 8% of thecandidates.

Physics A - Advanced Report on the Examination

18

Question 7 was also found to be easy (facility 84%), although alower discrimination index

than the first six questions points to the fact that even thebest candidates do not always fully

understand what is happening in circular motion.

Question 8, also on circular motion, involved a calculation.Candidates were rather less

successful with this question and the facility was 65%. However,the same question had been

used in the 1995 A level examination, when the facility was only59%. Almost a quarter of

the 2004 candidates chose distractor C.

The gravitational field strength at the surface of a planet andits relation with radius and mass

was the subject tested by Question 9. 61% of the candidatesselected the correct response, a

10% improvement over the pre-test facility. Distractor B, themost common wrong response,

was chosen by just over one in five of the candidates.

Question 10, with a facility of 66%, examined the variations ofelectric field strength and

electric potential with distance in a radial field. Distractor Dwas hardly ever chosen, with

wrong answers divided mainly between distractors A and B.

An unfortunate printing error, for which AQA apologises, meantthat an erratum notice had to

be issued for Question 11. This corrected the charge on Q from+6C to 6C. In the main,the candidates showed a good understandingof electric potential, causing the question to

have a facility of 75%. With a 40:60 division of the 100 mmseparation, it is not surprising

that the most common wrong response was distractor D (60 mm)when the correct one was A

(40 mm). Question 11 was the weakest discriminator on thispaper.

Question 12. Trajectories of charged particles as they passthrough electric and magnetic

fields ought to be a fairly simple topic, but the facility ofthis question improved only slightly,

from 55% to 57%, between pre-test and examination. Candidateswho did not understand

these topics were attracted in almost equal numbers todistractors B and D.

Questions 13 and 14, with facilities of 86% and 90%respectively, were the easiest questions

contained in this test. Each question had a pre-test facility of66%; the dramatic improvement

in facility seems to indicate that candidates are able to revisetheir work on nuclear

applications much more readily than most of the other topics inUnit 4. Question 14 was not

a particularly good discriminator.

Question 15 had a slightly unusual slant on the familiar topicof controlling a nuclear reactor,

where the effect of the control rods on the average kineticenergy of the neutrons had to be

considered. With a facility of 57% (up from 41% in thepre-test), the question proved to be

satisfactory and gave reasonable discrimination. Around onefifth of the candidates chose

distractor A, and a further one fifth chose C.

Report on the Examination Advanced - Physics A

19

Unit 4: PA04: Section B : Waves, Fields and Nuclear Energy

General Comments

This section of the Unit 4 examination gave candidates excellentopportunities to show what

they had learned. The examiners considered that it had been themost successful of all the

five papers set on Unit 4 since the introduction of Curriculum2000. Fewer candidates scored

low total marks, while a greater proportion scored marks of 20and above than in the previous

January Section B papers. Perhaps this is because centres arebecoming more discriminating

about the candidates they enter in January.

Some centres clearly have a policy of entering all their A2Physics candidates for the Unit 4

examination in January, despite the pressure this places on themto complete the necessary

preparations in four months of teaching. In these circumstancesthe January test seems to be

regarded by some candidates as a mock examination, before thereal test when they re-sit

Unit 4 in June. Many of these candidates are poorly prepared andconsequently obtain low

marks. On the other hand, some centres have a selected group ofable students who can cope

admirably with the January examination.

Penalties for transgressions over significant figures often hadto be imposed in Question

2(b)(i), where candidates strangely chose to write down answersthat included five or six

figures. Units were sometimes omitted from candidates answers toQuestion 4 (b), causing

the loss of the one mark for this part.

Examiners were pleased to see that many candidates made aserious effort to express their

answers in clear and coherent English and that the marks awardedfor the quality of written

communication had shown some improvement. Even so, the incorrectuse of technical

vocabulary frequently limits the mark that can be awarded to oneout of the possible two.

Question 1

In part (a), candidates often wrote about the principal featuresof a stationary wave (nodes

and antinodes) instead of addressing the conditions required forthe formation of a stationary

wave. It was expected that there would be reference to theoverlapping of two progressive

waves having the same frequency, similar amplitudes and equalbut opposite velocities.

Part (b) usually produced good responses, with the numericalvalues for wavelength and

frequency in parts (i) and (ii) both correct. Candidates weresometimes troubled more by part

(iii). Most seemed to realise that the period would be 4.0 msand that 3.0 ms implied three-

quarters of something. By no means all the candidates recognisedthat of an oscillation

would put the string in the undisplaced position. Manycandidates turned their thoughts to a

progressive wave, and went on to draw such a wave - which hadmoved of a wavelength to

the right in their diagram.

Question 2

Units of the various physical quantities related to fields andthe scalar/vector nature of them,

are generally not well known by the candidates. Part (a) showedthat the 2004 cohort were no

better than their predecessors. Six correct entries in the tablewere required for three marks,

Physics A - Advanced Report on the Examination

20

and it was very rare for all three to be awarded. The unit of Nm kg1

was accepted as an

alternative to J kg-1

for gravitational potential, but

candidates regularly put N kg-1

in the table. The unit of electric field strength was

known better, and that of magnetic flux density was usuallyshown correctly. Candidates

often resorted to guesswork when completing the second column ofthe table. Many did not

appreciate that the concept of potential arises from energyconsiderations and that it is

therefore a scalar quantity, whilst the other two quantities areforce-related and therefore

vectors.

Completely correct answers to part (b) were encountered in manyof the scripts. Since the

unit of E had already been tested in the table in part (a), nopenalty was imposed for wrong or

missing units in the answer to part (b)(i). A worrying error,made by a significant minority of

the candidates, was to equate the electric force on the particleto its mass, rather than to its

weight.

Question 3

This question was intended as a straightforward test of thesimple experimental phenomena

of electromagnetic induction and Lenzs law, as required bySection 13.4.4 of the

Specification. It is recognised that most A level candidateshave difficulty with these topics

and examiners were not very surprised by the many relativelyweak answers that were

written. Partial (or superficial) understanding of the phenomenaappeared to be the main

obstacle to progress. For example, in part (a) almost allcandidates appreciated that the

ammeter needle would deflect, but relatively few saw that itwould move one way, and then

the other way, before returning to zero. In this part, examinerssometimes wondered what

was going through the minds of candidates who wrote things suchas the current through the

ammeter would increase, and then return to its normal value.Perhaps this suggests that

these students had never previously encountered a centre zeroinstrument. Inappropriate use

of English also handicapped some candidates in part (a) typicalof which were answers that

began with the ammeter moves to the right.

Failure to address the question was the main difficultyencountered in most answers to part

(b). Instead of stating clearly that the acceleration of themagnet decreased, candidates

usually preferred to resort to woolly descriptions of the effecton the motion of the magnet.

Responses such as the magnet slows down and it decelerates wererejected. The

acceleration slows down was not a preferred response but it wasaccepted. The major

problem in part (b)(ii) was the failure of candidates to readthe question properly: this was

about the effect on the acceleration of the magnet as it leftthe coil, not after it had left the

coil. Consequently a large number of candidates followed abroadly correct deduction in (i)

by an incorrect one in (ii): they thought that the accelerationwould increase. The two

explanation marks in part (b) escaped all but the mostknowledgeable candidates. Some

understanding of what was induced and why, was almost aprerequisite to progress here.

Bald reference to Lenzs law was not considered to beadequate.

Even after presenting indifferent answers to the earlier partsof this question, many candidates

salvaged most of the three marks in part (c). Most appreciatedthat an incomplete circuit

meant that no current could flow, but many candidates wronglythought that the missing

ammeter would also prevent the induction of an emf.

Report on the Examination Advanced - Physics A

21

Question 4

The mathematical competence of the majority of candidates inthis question was much better

than has been seen in several recent papers and full marks werefrequently awarded. Previous

reports have emphasised that CV2 is a safer route to the energyof a capacitor than QV,

and in part (a) the message appeared to have got through to thecandidates. In part (b) the

main problems appeared to be with the meaning of micro in F andof kilo in k; the unit oftime constant was expected to be shown ass and not F.

The exponential decay equation was usually used correctly inpart (c), where approaches via

Q = Q0 e-t/RC

and V = V0 e-t/RC

were equally valid. Only a tiny minority of the candidates

attempted any other approach and almost all of them werewrong.

Units 5-9: PHAP: Practical

General Comments

Relatively few of the candidates appeared to be re-sitting theexamination and, as in the

previous examinations, the bulk of the entry was made up from afew centres with large

numbers of candidates. The number entered was similar to that ineach of the previous

Spring examinations and although there remains a significantrange of ability in the entry, the

impression gained was that the number of very weak candidateswas smaller than before.

The mean mark was one higher than that produced in Spring 2003when many candidates

struggled with question 1. This time, candidates found theplanning question much more to

their liking although this improvement was slightly offset by amore challenging second

question. When compared with Spring 2002, the current candidatesperformed slightly better

in question 1 and slightly worse in question 2 to produce analmost identical overall mean

mark.

All the assessment objectives provided similar discriminationand when a large sample of the

entry was analysed, every mark in the ranges for AO3a (Planning)and for AO3d (Evaluating)

was utilised in the distribution. All but one mark in each ofthe distributions for AO3b and

AO3c was utilised. It was interesting to find that for a typicalA grade and E grade

candidates alike, the fraction of the total mark obtained ineach of the four assessment

objectives was strikingly similar. In contrast to previousexaminations, few of the weaker

candidates gained the majority of their marks in AO3b and AO3c(Evaluating).

There was significant variation in the standard of presentationin the scripts but most

candidates managed to say as much as they felt necessary aboutquestion 1 without resorting

to supplementary sheets. There was less opportunity for extendedwriting in AO3d than in

previous examinations but this did not prevent some candidatesdeparting from, or

completely missing, the point of the question. It seemed that,as in previous examinations,

candidates had not taken sufficient care in reading the questionbefore starting their answer.

Some candidates lack a competent scientific vocabulary; the useof ampage rather than

current and voltage flowing rather than across betrayed theirlack of expertise.

However, others have become quite well versed in the terminologyof practical investigation;

dependent variable cropping up frequently as did anomalous(albeit in a bewildering range

of spellings).

Physics A - Advanced Report on the Examination

22

Graphical work is significantly better at A2 than at AS and in asmall number of cases this

was implausibly good: it was easily discovered that thesecandidates had invented their

results. Candidates should understand that the falsification ofdata is easily discovered and in

such cases the penalty is severe.

A majority of candidates failed to gain one or both of thesignificant figure marks in AO3b

because they failed to record their x values to the nearestmillimetre as required and because

the derived (x2) data was given to 2 and not 3 significantfigures. The thinking seemed to be

that because they, in the course of the experiment, set the xvalue to a convenient value, e.g.

40, 50, 60 cm etc., then these data could logically be recordedto the nearest centimetre.

Candidates should understand that data, whether for thedependent or independent variable,

should be recorded in a way that is consistent and appropriateto the method of measurement

being employed in this case, a distance read between two pointson a metre ruler calibrated

in millimetres.

A2 candidates proved to be generally dependable withmathematical processing. The

elevation of the period, T, to the fourth power (and the reverseprocess when determining TSin (e)(i) was reliably done by all.Many, having chosen scales for their graphs that prevented

a direct reading of the intercept being made, were happy to usealgebra instead, although

some forgot that their result for G should have a negativevalue.

The candidates appeared to have had sufficient time to completeboth parts of the

examination and in instances where parts of questions weremissing, it appeared that lack of

practice on the part of the candidate was the cause.

Question 1

Candidates were presented with a scenario in which an aluminiumring, placed over a vertical

soft iron rod, fell through a magnetic field produced by a coilsurrounding the rod. They

were told that when an alternating current was passed throughthe coil, the time that the ring

took to fall through the magnetic field increased slightly. Theywere required to describe a

method of investigating how this small change in transit timemight be affected if some

measurable change was made to the apparatus.

Although most candidates seemed to appreciate what was going onand had useful and

usually correct ideas about what could be accomplished, therewere some oddities about

many of the answers seen. A significant number failed to takeaccount of the clue given that

the transit time was only slightly increased and describedhand-held timing measurements

that could not achieve successful results. Some, it seemed, arepersuaded by the fact that

stopwatches record times to 0.01 s as valediction for

claiming this as the precision of the instrument. Othercandidates appear to have great

confidence in any instrument that is fitted with a digitaldisplay (this point being made by

several in relation to the ammeter they intended to use).

Many diagrams the candidates provided did little or nothing toadd to the information already

given in the question paper; some diagrams did more harm thangood by including incorrect

circuits that would prevent the experiment from working asdescribed (e.g. a voltmeter in

series with the coil). The most common circuit diagram error wasthe incorrect

representation of the ac power supply.

Report on the Examination Advanced - Physics A

23

To earn one of the three possible strategy marks, candidates hadto identify from a wide

choice one variable that could affect the transit time of thering. While adjusting the current

was a clear favourite for the majority, others chose to vary thenumber of turns on the coil,

the frequency of the ac or the thickness of the aluminium ring.Sadly some, in their

enthusiasm to communicate, forgot to vary anything at all orvaried more than one thing at a

time.

Given that the situation hinged around the change in the transittime caused by the current, a

strategy mark was given if candidates mentioned that (as a meansof comparison) the time

was measured with zero current, but relatively few made thispoint. The third mark was

awarded for some explanation of how the results would beanalysed to discover whether a

link had been established between variable and transit time.Most candidates suggested the

data be shown in graphical form and providing some justificationfor this step was given, the

mark was awarded. Although not required, some candidates made aprediction about the

outcome: many felt that direct proportionality between currentand transit time was

guaranteed but others confidently asserted that these variableswould be linked with an

inverse relationship.

Marks were awarded for performing some suitable electricalmeasurement (usually current

with an ammeter) provided the circuit shown in any diagram wouldwork. This mark was

awarded whether current was a variable or a control factor (e.g.in the case where the number

of turns on the coil was to be changed). If the frequency of theac was to be varied a cro or

data logger was required. To measure the transit time, two lightgates and a data logger were

expected; the idea that light gates could be connected to acomputer was not given full

credit. Some candidates described arrangements similar to thatused to measure the

acceleration of freefall, apparently ignorant of the fact thatan aluminium ring could not be

held in place by an electromagnet.

Three marks were available for identifying factors that shouldbe controlled. Two of these

were to do with the interaction between the ring and theelectromagnetic field around the coil:

if, for example, the candidates investigation involved varyingthe current, then the control

factors could be the number of turns on the coil and thefrequency of the alternating current.

Another mark was awarded for identifying a control factor thatmade the timing a fair test:

candidates rarely said enough to give a completely accuratedescription of what should be

done but this point was marked generously with credit given forsaying that the same stop and

start points were used or that the ring was released from thesame height. Candidates

generally scored at least one, often two, but rarely three ofthese marks.

Marks for procedures and difficulties were infrequently awarded.Those who advocated hand-

held timing methods were given no credit for saying thatrepeating and averaging could

improve their results. Similarly, no credit was given for thesuggestion that the reliability of

hand-held timings are improved by getting several people tocollaborate in the exercise.

Marks were awarded if candidates suggested that extending thetransit time by using a longer

coil/rod would reduce uncertainty. Details such as ensuring thatthe ring fell smoothly and

checking the coil and rod were vertical were also givencredit.

Physics A - Advanced Report on the Examination

24

Question 2

Candidates were required to investigate how the period of aV-shaped pendulum depended on

the horizontal separation between the upper ends of thesupporting strings. In contrast to the

observation in the previous report that many candidates seemedto have been short on

experience with shm exercises, this group fared better inperforming their experiment.

However, the candidates found each section of the questiontesting in other ways and the

mean mark was slightly below that for each of the previousexaminations.

In AO3b (parts (a), (b) and (c)), at least one and often twomarks were withheld for recording

data to an inappropriate number of significant figures. Manycandidates also failed to make x

measurements over a sufficiently wide range (at least 30.0 cmwas required). The quality

mark was awarded if four of the five plotted points were closeto the line and with most

timing, sufficient cycles to determine the period, T, (at least20 or 20 were expected); thismark was frequently awarded. Thetabulation mark was given except in the isolated

instances where nT had been confused with T.

Candidates proved reliable in calculating the derived data setsand the graph and its analysis

(assessing AO3c) was generally sound. Some missed or gaveincorrect units in labelling the

axes and there were the usual crop of scales that werecompressed to include the origin.

Many forgot to record the gradient as being negative but thenumerical answer was often in

the range 3.90 to 4.20, for which full credit could be givenCandidates were not penalised for

any missing or incorrect units with their answer for G.

In part (e) (assessing AO3d) candidates were required to findthe period of the pendulum for

which the horizontal separation of the strings was zero, a taskto which nearly all proved

equal. Where the intercept was not directly obtainable, the useof algebra proved an

acceptable alternative and most were able to deduce a result forTS between 1.35 s and 1.60 s,

as expected. Many candidates knew the expression for the periodof a simple pendulum (or

found it on the data sheet) and were usually able to obtain aresult for S that was in close

agreement with that for TS. Exceptionally, some candidates mixedunits on substituting data

into the expression but it was unusual to find candidates whocould make no progress with

this part.

In (e)(iii) some overlooked the information contained in thequestion that they were to

assume the percentage errors in T and x were the same and wroteinstead about the

procedures they had followed to measure each variable. Suchdiscussions generally

persuaded them that the error in x was the larger. Most though,saw that by raising T to the

fourth power (with x only raised to the second power) it wouldbe the error in the period that

would contribute most towards the uncertainty in TS.

Report on the Examination Advanced - Physics A

25

Units 5 - 9: PHAC: Coursework

In most cases Centres used investigations which wereappropriate, allowing their candidates

access to the full range of assessment criteria. Experiments onsimple harmonic motion,

optical experiments on lenses and charging/dischargingcapacitors were the most popular and

these proved to be successful in allowing a full range of marksto be achieved.

The general comments on presentation of coursework and issuesraised by moderators are the

same as those made on the AS work. Please refer to the detailedcomments which appear on

pages 12 - 14 of this report.

Units 5 - 9: PHA5/W - PHA9/W: Section A : NuclearInstability

Section A of Units 5 - 9 consists of a question on nuclearinstability and is common to all

these units.

The majority of candidates understood the requirements of part(a) and were able to give

three arrows as a single route, but a significant number did notknow the correct direction of

both types of decay. Horizontal and vertical arrows werecommonly seen. A common

mistake was an apparent interpretation of the N on the verticalaxis to mean nucleon number

instead of neutron number, as the question stated. Severalcandidates had very little idea how

to proceed and drew random lines which finished well away fromthe daughter nucleus.

Part (b), where two equations had to be completed was not welldone with few candidates

scoring full marks and many scoring zero. The Ni nuclide oftenappeared as Cu, X or Y,

frequently with incorrect values in the subscript and/orsuperscript and occasionally with

different values in the decay mode. Weaker candidates often putthe electron on the wrong

side of the decay equation. Neutrinos appeared in most answers,but most frequently as a

neutrino in one decay mode and an antineutrino in the other.

particles were the choice of the great majority of candidatesfor the scattering particles inpart (c) and for many candidatesthis was their only mark for this section. For most

candidates, the requirement to describe the main physicalprinciple of the scattering process

was interpreted as write as much as you can about Rutherfordsscattering experiment,

resulting in answers which were imprecise and demonstratedlittle more knowledge or

understanding than that covered at GCSE. The idea that theexperiment gave an upper limit

for the nuclear radius was missed by nearly all candidates. Thesmall minority of candidates

who described electron diffraction by the nucleus usuallyanswered the question well,

demonstrating appropriate knowledge about the intensity minimumand the information

gained from it. These candidates seemed to have a deeperunderstanding of the experiment,

perhaps due to the fact that this was a new situation which hadbeen taught in more detail at

this level.

Physics A - Advanced Report on the Examination

26

Unit 5: PHA5/W: Section B : Astrophysics Option

General Comments:

Most candidates were able to attempt all the questions and fullmarks were achieved in each

question. Mathematical problems were generally answered well,although marks were lost

for failing to understand which units should be used for some ofthe physical quantities.

Answers requiring more extended writing tended to produce morevariable responses. Often,

full marks were missed due to lack of detail, or irrelevantinformation. More care should be

taken to learn the important features of different astronomicalphenomena. Many candidates

were able to score both marks for their quality of writtencommunication.

Question 2

This question was generally very well answered with manycandidates scoring high marks.

In part (i) most candidates correctly identified the tworequired properties of the image,

although several repeated the question by stating that the imagewas magnified. Another

common error was stating the image to be virtual. This lasterror would then be carried

forward to part (ii).

The ray diagrams drawn in part (ii) showed a big improvement intheir clarity compared with

those of previous years. Centres had clearly acted on thecomments in previous reports and

insisted that their candidates used a ruler and took care indrawing diagrams. A clear

misconception with many candidates is the position of theprincipal focus. It was commonly

labelled where the two rays crossed i.e. at the image. Thiserror is probably due to the fact

that the concept is often introduced by drawing parallel raysentering the lens, so that the

image and principal focus coincide and candidates fail torecognise the special nature of the

situation in the question. Candidates should be alerted to thismistake.

In part (iii) most candidates substituted correct values intothe lens formula and calculated the

lens power correctly. The most common error was associated withthe unit, with many

candidates continuing to write watt as the unit of lenspower.

Question 3

Many candidates achieved very good marks in this question,although very few obtained the

maximum available. In part (a) the mark for the definition ofthe light year was gained by

virtually all candidates, although some failed to expressthemselves sufficiently clearly. Very

occasionally answers which suggested that a light year was ameasure of time rather than

distance were seen. By contrast, very few candidates wereawarded the mark for stating what

is meant by the parsec. This is clearly on the specificationalthough trigonometric parallax is

not longer required. The best answers stated the relationshipbetween the angle, the AU and

the parsec, and included a diagram to make it absolutelyclear.

A calculation using apparent and absolute magnitude is a commonfeature of this paper and

most candidates responded well to this example in part (b).However, far too many failed to

convert the distance (given in light years) into parsec beforemaking the substitution in the

equation. The use of incorrect units was a common feature in thepaper this year. Some

candidates mixed up the apparent and absolute magnitudes. Thiswas treated as a physics

error and was therefore heavily penalised. In part (ii) mostcandidates correctly identified

Report on the Examination Advanced - Physics A

27

that spectral class A is hotter than spectral class G. The bestcandidates justified their

answers by quoting the OBAFGKM range, giving typicaltemperatures for the two classes.

Part (iii) required more careful justification. There was someclear confusion as to whether

the stars were the same brightness. The best answers correctlyidentified star A as the

smaller, comparing the temperatures of the two stars, and usingStefans Law to justify the

answer.

Questions on resolving power are another common feature of thisoption. In part (c) the

correct expression was generally used but most candidates lost amark by not converting the

angle quoted into radians before substitution.

Question 4

This was a question that many candidates found difficult, withonly a few scoring maximum,

or near maximum marks. In part (a) (i) awarding marks to theblack body radiation curve for

the Sun was often generous, but there were many candidates whohad no idea of the shape or

the main feature of the curve. Examiners were looking for asteep curve on the left hand side

of the peak, with a much more gradual curve towards zero on theright hand side. Good

answers showed an intercept on the low frequency side of afairly narrow peak. There were

many different positions given in part (ii) for the region ofultraviolet absorption. Candidates

were rewarded for marking a region to the left of the peak,within the overall curve. In part

(iii) the fairly common answer that absorption was due to theozone (frequently spelt o-zone)

seems to suggest that some candidates believe that this is aregion of the atmosphere rather

than a gas. Benefit of the doubt however was given for thisanswer. Many candidates in part

(iv) could not link ultraviolet absorption with the effect onthe wavelength of the peak and

therefore on the calculated temperature using Wiens Law. Therewas much evidence that

candidates were not familiar with the problem. Many discussed,for example, the absorption

of the light by the atmosphere of the star. Some credit wasgiven for answers which could

explain why the absorption of light could suggest the star wascooler, without reference to

Wiens Law.

The fairly straightforward calculation in part (b)(i) wasusually answered well, although there

was evidence of some confusion between the prefixes G and M inthe frequency values. The

identification of the Doppler effect in part (ii) was an easymark that was gained by almost all

candidates. The calculation in part (iii) identified moredifficulties. Although the process

actually involves a double Doppler shift because the Moon actsboth as a receiver and a

source (reflecting the received signal) this was ignored whenmarking and full marks were

awarded if candidates only calculated the single shift. Therewas much confusion over the

use of the equation however. Some candidates apparently believedthat the in the equationwas a variable. Very few candidatesanswered fully and stated that the increase in frequency

meant that the Moon and Earth were getting closer. Some errorsled to answers at or greater

than the speed of light. There was no evidence of candidatesbeing wary of these answers or

suggestions that they may have made a mistake. Credit was notawarded for consequential

errors leading to these answers as candidates should realise,particularly with speed

calculations, that when an answer is ridiculous or impossiblethey should be encouraged to

comment on it.

Physics A - Advanced Report on the Examination

28

Question 5

Unfortunately this was incorrectly labelled as question 4 in thepaper but this printing error

did not cause candidates any problems. Almost all candidatesmanaged to write something

about the Big Bang. Those who gained no credit includedcandidates who described the

processes in a supernova. The expansion of the Universe alsocaused problems with some

students. It was commonly suggested that everything wasexpanding and that Hubbles red

shift was measured for stars, with no mention of galaxies.Background radiation was often

given as evidence for the Big Bang, but this was not givencredit unless it was made clear

what form this radiation takes.

The inclusion of this subject in the Specification givescandidates the opportunity to read

about one of the most important theories in modern cosmology.Unfortunately too many

answers were vague and ambiguous and suggested little moreknowledge or understanding

than that of the general public.

Unit 6 : PHA6/W : Section B : Medical Physics Option

General Comments

Although the examiners considered all the questions to beaccessible only a few candidates

gained high marks. Question 2 required a ray diagram to bedrawn. This is the first time for

a few years that such a question has been set and it appeared tocatch the candidates by

surprise since, in general, the diagrams were very poor.

Question 2

This question produced the poorest answers in the whole paperand it was clear that many

candidates had little real knowledge of the situation outlinedin the question. In part (a) the

large majority of candidates failed to appreciate that the imagewas virtual and did not apply

the correct convention in the calculation involving the lensformula. More candidates worked

out the magnification correctly, but a noticeable number wronglyused object distance

divided by image distance.

In part (b) only two correct diagrams were seen. Candidatesappeared to have very little idea

of how to construct a ray diagram and of those that did theyfailed to realise the relevance of

the virtual image.

The best answers appeared in part (c)(i). In part (ii), clearthinking was missing in most of

the answers submitted. Even allowing for an incorrect answer inpart (a)(i) to be carried

forward, very few candidates produced a correct answer. Manywere unable to even start the

calculation and of those that did, the majority stated that theaided far point would still be at

infinity.

Report on the Examination Advanced - Physics A

29

Question 3

Several candidates gained full marks for this question. In part(a), many lost the first mark by

defining intensity in terms of energy instead of energy persecond or power. Many

candidates gave a correct explanation of attenuation but acommon misconception was that

attenuation was caused by the spreading of a wave from a pointsource according to the

inverse square law.

In part (b), although many candidates carried out thecalculation correctly a common error

arose from the fact that the units were not read carefullyenough and watts was used as the

unit of I0 instead of the given mW.

Question 4

Candidates provided good answers to this question and it earnedthe highest marks on the

paper. In part (a) most candidates were able to describe theaction of the heart and full marks

were awarded quite often. Marks were lost when candidates wereunable to express their

ideas clearly and occasionally four steps were described asatrium to ventricule to atrium to

ventricule.

Answers to part (b) also saw many full marks being awarded butmarks were lost for

including wrong answers alongside the correct ones, e.g. in part(i) stating that both

potassium and sodium ions entered the membrane.

Question 5

Although a number of candidates gained full marks, this questionproved to be difficult for

some. Answers to part (a) often lacked the clarity needed to beawarded the allocated marks

and usually candidates were only awarded one or two marks of thepossible three. A number

of candidates did not really understand what was required by thequestion and tried to answer

in terms of an image intensifier or intensifying screens. Somecandidates even discussed the

use of a grid to enhance the picture by reducing scatteredX-rays reaching the film.

It was very pleasing to find that the calculation in part (b)was carried out correctly in a

number of cases. Some candidates failed to rearrange theexponential equation correctly but

they appeared to be fewer in number than in previous years.

Physics A - Advanced Report on the Examination

30

Unit 7: PHA7/W: Section B: Applied Physics Option

General Comments

It was clear that almost all candidates had been well preparedfor this paper and the quality of

answers in most cases ranged from good to excellent. Almost allcandidates attempted every

question and there was no evidence of a shortage of time on thepaper. With few exceptions,

the standard of English and the presentation were good. Therewere few problems with the

use of units in some answers, but more candidates than is usualin this January paper were

penalised for the use of an inappropriate number of significantfigures in a numerical answer.

Question 2

Most candidates found this question straightforward and manyscored full marks. In part

(a)(i), the unit of torque was almost always present andcorrect; an unexpected and

remarkable improvement on previous papers. In part (b), somecandidates worked out a

value for the moment of inertia of one tube only rather than theeight in use and rather more

failed to add to this the moment of inertia of the centrifugeitself to find the total moment of

inertia. Part (c) was almost always done well and usuallycompletely correctly.

Question 3

Almost all candidates answered this question very well, withmost scoring full marks in part

(a) and many scoring at least two of the available three marksin part (b). In part (b)(i), the

correct equation was almost always seen but a value of 12 kJwas

occasionally used in place of the correct value of 36 kJ for theenergy remaining after the

stamping operation. The unit of angular impulse was sometim