(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

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