GCE 2002

January Series

Report on the Examination

Advanced Subsidiary - 5451Advanced – 6451

PhysicsSpecification A

Advanced Subsidiary

Advanced

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CONTENTS

Specification A

AS Units

Page No.

Unit PAO1 Particles, Radiation and QuantumPhenomena………………………………………………………………4

Unit PAO2 Mechanics and Molecular KineticTheory………………………………………………………………………7

Unit PHA3/P Current Electricity and ElasticProperties of SolidsPractical……………………………………………………………………9

Unit PHA3/C Current Electricity and Elastic Properties of SolidsCoursework………………………………………………………………11

Unit PHA3/W Current Electricity and Elastic Properties of SolidsWritten…………………………………………………………………….13

A2 Units

Page No.

Unit PAO4 Waves, Fields and NuclearEnergy…………………………………………………………………….16

Units 5-9PHAP

Practical …………………………………………………………………19

Units 5-9PHAC

Coursework………………………………………………………………22

Unit PHA5/W Section A: Nuclear Instability…………………………………...23

-PHA9/W

Unit PHA5/W Section B: Astrophysics Option………………………………….23

Unit PHA6/W Section B: Medical Physics Option…………………………….24

Unit PHA7/W Section B: Applied Physics Option……………………………..26

Unit PHA8/W Section B: Turning Points in Physics Option……………….27

Unit PHA9/W Section B: Electronics Option……………………………………29

Mark Ranges and Award of Grades……………………………………………….….31

Physics

Specification A

Advanced Subsidiary Examination

Since this was the third time that some of the examination papers have been set, the

candidates have by now become familiar with the format of the papers and the type of

questions.

As in previous examinations all the principal examiners were satisfied that the papers had

been fair and had performed well, although there was some evidence that the marks had been

depressed slightly compared with the Summer 2001 papers. It is very pleasing to report that

the practical paper PHA3/P proved to be significantly more accessible than the corresponding

Summer 2001 paper.

A significant number of candidates were taking the examination for the second time. This

number ranged from 25% of he total entry for PA01 to 65% in the practical component of

PHA3/W and 95% in the corresponding coursework component. There was however no

valid reason to think that these repeating candidates were weaker than candidates in 2001.

There was no evidence in any of the papers to suggest that candidates had been short of time

nor was there any strong evidence that certain topics had not been covered.

With so many candidates taking the examination it is unavoidable that there will be some

incorrect use of significant figures and units, but it is pleasing to note that no examiner made

a pointed reference to these errors. This would suggest that candidates are becoming more

aware of the importance of significant figures and units and consequently not being

penalised.

Awarding the Quality for Written Communication marks appeared to go the same way as in

previous examinations, although there was an impression that there seemed to be a smaller

proportion candidates not gaining any marks.

Unit 1 : PA01 : Particles, Radiation and Quantum Phenomena

General Comments

Although the paper was considered to be slightly more demanding than the corresponding

paper in 2001, the award of full marks was not uncommon because excellent candidates had

been entered. In contrasting with this however it appeared that there were far more

candidates at the lower end of the mark scale than previously and many appeared not to have

been prepared fully for the examination.

Report on the Examination PhysicsA- Advanced

5

Question 1

Although parts (a) and (b) followed the usual pattern of the first question on the paper, the

addition of part (c) caused difficulties and full marks were few and far between. In part (a) a

significant minority of candidates gave wrong answers and in part (b) almost all candidates

failed to change the chemical symbol to Co, preferring to stay with Ni.

In part (c)(i) at least half the candidates gave the correct symbol for tritium but the remainder

showed a variety of mistakes in the values of the superscripts and subscripts, ranging from

3

1H to

1

4H. In part (c)(ii) only the top few percent of able candidates made a reasonable

attempt at the calculation.

Question 2

This question provided very good discrimination with the majority of candidates failing to

make any worthwhile attempt at all the calculations. Although a significant number of

candidates completed part (i) correctly, many of the others simply invented formulae to fit the

data provided e.g. energy = hλ appeared quite often. In part (ii) the majority of candidates

failed to use the de Broglie relationship, but instead chose to misinterpret the question and

tried to find the speed of an electron having the same energy as the photon.

Question 3

Traditionally, calculations connected with the photoelectric effect perform better than written

descriptions of the effect. Describing the event proved to be a skill not acquired by many of

the present candidates. There appeared to be a general lack of basic understanding of the

photoelectric effect which could not be attributed simply to a lack of communication skills.

In part (a) most candidates elected to repeat the information given in the question by

continually referring to the frequency of the photon rather than discussing the energy of the

photon. It was also clear that at least half the candidates could not distinguish between the

process of emission of an electron from a metal surface and ionisation of an atom.

The calculations in part (b) were, on the whole, performed well but some of the problems

which appeared were omitting the units in part (i) and weaker candidates wrongly converting

J to eV in part (iv) through multiplying rather than dividing by the charge e. There were a

number of significant figure errors in this part of the question.

Question 4

The answers to this question showed that although a large number of candidates had some

knowledge of the subject, they had not covered the specification material adequately. This

lack of knowledge was apparent in the ray drawings in part (a), where the typical mark was 2

out of 4. There were some surprising aspects of scoring marks in this section, e.g. two marks

were available for drawing the paths of the rays emerging into air and being refracted away

from the normal. These two marks covered the same idea but a majority of candidates only

scored one.

In part (b)(i) only about a quarter of the entry calculated that the angle of incidence at the

boundary was 20o, but then managed to score reasonably well through the use of

consequential errors. There were some good attempts at part (c) by a minority of candidates.

Most candidates were uncertain whether to use a single refractive index or a relative

refractive index throughout the calculations in parts (b) and (c).

Question 5

Questions on fundamental particles have usually enabled the better candidates to score quite

heavily and this question turned out to be a good discriminator for the middle standard

candidate. In part (a) a large percentage of candidates had trouble converting from eV to J, as

in question 3. In part (b) weak candidates appeared to be taking random guesses at the

answers in the table but even the middle standard candidates were not aware of the instability

of the neutron.

Part (c) performed much better with most candidates knowing the name of an exchange

particle other than a W boson and also knew the interaction for which their chosen particle

was responsible. About a quarter of the candidates failed to complete the Feynman diagram

successful.

Question 6

This question again showed good discrimination and in particular showed up the weaknesses

of the poorer candidates. Part (a) was usually performed well by most candidates whereas

part (b) was answered incorrectly by a large majority of candidates. It was a common

misconception in the answer to part (b) that the neutron was the most stable baryon.

It was common in part (c) for more than half the available marks to be earned, but often this

was due to consequential errors. It was interesting to note that candidates would often work

through conservation of lepton number, baryon number and strangeness but failed to consider

conservation of charge. Consequently, part (c)(i)(A) was a stumbling block for most

candidates.

Question 7

Most candidates were aware of the answer to part (i) but failed to gain the mark by not stating

explicitly that the electron was removed from the atom. Answers such as, ‘the atom goes to

level n = ∞‘ were common. In part (ii) the energy required to ionise the atom was often

quoted as a negative quantity.

Part (iii) tested candidates’ communication skills. Most candidates used much of the available

space to describe the process of excitation but many were not clear as to how the two photons

were produced. It was common to read statements such as ‘If the energy drop is very large

two photons, not one, are produced’ or ‘Sometimes the single photon is replaced by two, each

sharing the energy equally’.

Report on the Examination PhysicsA- Advanced

7

The transition between energy states in part (iv) was often given the wrong way round with

an electron in the ground state moving to level n = 5. In part (v) the frequency of the emitted

photon was calculated successfully by most candidates with the remaining candidates falling

into two groups; those who failed to use the factor of 10−18

in the energy value and those who

failed to use the equation ∆E = hf.

Unit 2 : PA02 : Mechanics and Molecular Theory

General Comments

The paper produced good discrimination and a full range of marks, but was found to be

slightly more difficult than the corresponding paper in January 2001. The paper required

more explanations and less numerical work than the 2001 papers, but this did bring it more

into line with the prescribed balance of objectives. There were no inaccessible questions

although some marks were hard to come by and were only earned by the most able

candidates. Calculations were usually well set out and most students seemed aware of what

was required in the assessment of quality of language. Significant figure errors were in

evidence but incorrect or missing units were comparatively rare. There were no areas of the

Specification for which candidates had not been prepared.

Question 1

Parts (a) and (b) produced good responses although a significant proportion of candidates did

concern themselves with rate of change of speed rather than velocity. Part (c) was less well

answered and proved to be a good discriminator as only the most able candidates were able to

sketch the correct graph.

Question 2

In part (a) the majority of candidates gained high marks for correct plotting of the graph, the

only major error being due to poor choice of scale. Determining the average kinetic energy of

gas molecules at 350o from the graph and calculating the gradient of the straight line was

usually carried out correctly, but very few candidates, however, were able to deduce a correct

value for the Boltzmann constant. The vast majority assumed that the gradient equalled the

constant.

Part (b) of the question was answered with mixed success. A significant minority could not

explain what was meant by an elastic collision and part (iii) was not well answered since

there appeared to be some confusion as to what exactly was required. It seemed a common

misconception that absolute zero occurred at –273 K.

Question 3

In general this question was answered well and many candidates secured full marks.

The only difficulty with part (a) was that the horizontal and vertical components of the force

were not shown as originating from the point on the kite through which the force F acted.

Although weaker candidates were unable to deduce correct values for the vertical and

horizontal components of F in part (b), they were able to make a reasonable attempt in part

(c) at combining the two components to obtain the magnitude of F.

Question 4

As with the question on moments in previous examination papers, this question was usually

answered well, although explanations as to why the pivot should be moved to the right tended

to be a little vague. In general, attempts at the calculation in part (c) were well done and

balancing of moments seems to be a well understood concept.

Question 5

Candidates appeared not to understand clearly the term, resultant force, in part (a) and often

confused resultant force with the resistance forces or the driving force. Such a misconception

led those candidates to deduce that the resultant force increased rather than decreased.

In part (b) a significant proportion of candidates calculated the kinetic energy incorrectly, by

ignoring the need to square the velocity. The calculation in part (c) was generally well done

although answers were often left as a fraction which incurred a significant figure penalty.

Question 6

The responses to this question were generally good and candidates were able to obtain the

correct answer to part (a) and conduct a meaningful discussion in part (b) in terms of energy

changes. Unfortunately a minority of candidates did use the equations of uniform

acceleration in an incorrect context in this question.

Question 7

The main problem faced by candidates when answering this question was the confusion

which arose when deciding what to call the opposing force. Many candidates identified it as

upthrust when they meant drag and a significant minority discussed air resistance. There was

also a tendency to state that the drag force become equal to the acceleration of the ball

bearing due to gravity rather than its weight.

Part (b) proved to be a good discriminator with only the best candidates producing answers

for which marks were awarded.

Question 8

There were excellent attempts at the calculations in part (a) although there were fewer

instances of full marks being awarded than was the case for a similar question in the

corresponding Summer 2001 paper. There was some uncertainty with negative signs and

very often negative signs were conveniently dropped when it came to taking square roots.

Report on the Examination PhysicsA- Advanced

9

The descriptive section in part (b) proved to be quite discriminating with the weaker

candidates obviously not quite sure as to the context of the question.

Unit 3 : PHA3/P : Practical

General Comments

The entry came from approximately 90 centres, many with only single candidates who were

presumably re-sitting the unit in order to improve on the mark obtained previously. This

impression was reinforced by the generally better quality of work seen in these scripts when

compared with Summer 2001 practical paper, suggesting that candidates had benefited from

being exposed beforehand to live examination questions. The experimental arrangement

worked as expected and few centres reported difficulties in the assembly of the circuit in

question 2. As is often the case in the age of digital meters, the demands of gathering and

processing measurements were minimal and most candidates found the graph easy to draw.

However, compared with Summer 2001, the subsequent processing was far more demanding.

The standard of written communication was mostly good, although a tendency persists to

write far more than is necessary: supplementary sheets should not be required unless a

candidate feels the need to restart an answer. There was no evidence seen that candidates

were short of time. The bullet points on page 5 of the examination paper are intended to help

candidates structure their answers and most now take their cue from these. Greater attention

should be paid to explaining how difficulties in obtaining results are resolved: bland

statements about repeating the experiment to improve accuracy are not given credit.

Most candidates understood that consistent tabulation of data was required with all raw data

given to the same uncertainty, but it was noticed that some candidates choose graph scales

that maximise the use of the page without considering the need to plot data points easily.

Scales where major grid markings represented multiples of three or four were seen. When

this type of scale made it difficult to check the accuracy of the graphical work or gradient

calculations, marks were deducted. Several candidates did not appreciate that ratios have no

units.

The distribution of marks was wider than in the previous examination with more marks in

general being gained for the planning and design of an experiment in question 1. However,

there are still candidates who can make little progress with this question and the majority of

candidates only scored 3 or 4 of the 8 marks available.

Question 1

Candidates were required to design an experiment to find the fraction of stored energy that is

returned by the catapult.

Candidates were expected to describe an experiment in which elastic potential energy was

transformed into kinetic energy (and then possibly into gravitational potential energy). Some

candidates chose to recycle information given in the question by describing an experiment to

investigate the loading-unloading cycle for a rubber band. Such accounts often gave details

of arrangements more suitable for describing the Young modulus of the material of a wire. If

the suggested arrangement could not transfer energy to a projectile, full credit was not given.

It was unclear from some of the diagrams drawn whether the arrangement showed a projectile

being launched horizontally or vertically, but it was often possible to give credit for details

omitted from the written account when a clear diagram made the intentions clear.

Most candidates used the expression ES = ½Fs to calculate elastic potential energy and this

was accepted, although better answers considered determining the area under a force-

extension graph. Many candidates wrongly stated that the change in length of the catapult

cord was s. Others confused the displacing force F with the weight of the projectile.

It was common to find weight being confused with mass, the idea of ‘weighing’ a mass using

‘scales’ being seen frequently. Some candidates were aware what a newton meter was, but

very few managed to spell the name accurately. Candidates were generally careful to state

what they would use to make measurements with, the exception being the force used for the

displacement of the catapult. Statements such as ‘Suspend a known mass from it’ was not

accepted unless it was clear how the mass was known and how the extending force could

subsequently be calculated.

While methods of obtaining elastic potential energy were generally acceptable, many

candidates had difficulty in explaining how to measure either the kinetic energy or the

gravitational potential energy of the projectile. For vertical motion, many candidates

assumed that hand-held timing devices would yield results suitable for determining the speed

of the projectile as it left the catapult. These answers often failed to take account of the

deceleration of the projectile and few candidates made use of the equation ν = 2gh. Many

candidates also suggested that hand-held timing devices would be suitable for determining

the speed if the projectile was fired horizontally. Better answers recognised the limitations of

these methods and suggested the use of light gates linked to a microcomputer or data logger.

Other suitable methods seen involved transferring the energy stored in the catapult to a

dynamic trolley free to roll down a friction-compensated runway.

It is pleasing to report however that, unlike the Summer 2001 examination, many candidates

did get the basic physics right and most of them could explain how the fraction of stored

energy that would be usefully returned could be calculated.

Candidates were also required to identify any factors that would need to be controlled in

order to obtain reliable results. The favourite answer was ensuring that the same elastic cord

was used throughout or, in the case of upward projection, ensuring that the projectile only

moved vertically.

Most candidates continue to have little success in explaining how difficulties in their

proposed experiment are overcome and they should realise that repeating a measurement does

not in itself reduce uncertainty unless results are averaged or otherwise help to identify

anomalous data. Answers tended not to be specific in these respects. Credit was given where

measures were suggested which would increase the magnitude of a measurement so as to

reduce the uncertainty in it.

Report on the Examination PhysicsA- Advanced

11

Question 2

Candidates were required to investigate the potential difference across parts of a resistor

network as the current in the circuit was varied using a variable resistor.

Even though the initial measurements were included with the main sets of results when taking

account of consistency in tabulation, the majority of candidates recorded all their data in

appropriate fashion. Only few candidates misread ammeter scales but there are still those

who see the full-scale setting e.g. on a multimeter, as some sort of scaling factor with which

to multiply the meter reading. No errors were found in the subsequent processing involving

the sub-multiple (millamps). Some candidates interchanged the initial current readings

through carelessness or by failing to appreciate that the maximum resistance of the circuit

corresponded to the smallest current reading. The ratio I

I

2

1

and, later on, G

G

1

2

were

frequently given with a unit.

Units were rarely absent in the table headings and the range of data sets was usually

adequate. It was rare to find a script in which the readings for VCB were not recorded as

negative.

The quality of data was generally good enough to find points close to (or usually on) each

best-fit line with the lines passing through the origin of the axes-system. Graph scales were

almost universally chosen to maximise use of the page, but awkward scales made

interpretation difficult. Weaker candidates tended to overlook the unit on the voltage axis.

Gradient calculations were often absent and evidence about how G1 and G2 were obtained

could not be ascertained from the graph. Many candidates who did show their method, failed

to use sufficiently large y-steps or x-steps in their calculations.

In part (f)(i) candidates were expected to mention the need to accurately determine the best-

fit line or gradient of their graph but too many answers simply indicated the need to produce

a ‘good’ graph or ‘accurate results’. In part (f)(ii) only few candidates referred to their earlier

results, as instructed in the question, but the majority correctly explained that the maximum

resistance of the variable resistor was greater than the resistance of the network of resistors.

Some candidates falsely argued that the network resistance must be the least because the

resistors were in parallel. It was rare to find scripts where the effect on I1 and I2 of the

change in the variable resistor proposed in part (f)(iii) was incorrectly stated.

Most candidates find the style of question 2 very accessible and few of them score less than

half the available marks. It is, however, disappointing to note that there were no scripts

where all the marks had been awarded.

Unit 3 : PHA3/C : Coursework

Of the 700 candidates presented for the coursework element of this paper, almost 65% were

carrying forward marks from the Summer 2001 examination. Comments in this report are

therefore made on the basis of a relatively small number of seen scripts.

In general, few adjustments were made to marks submitted by centres, but when moderators

did find it necessary to make an adjustment, it was often considerable. Major adjustments

were, almost without exception, due to a failure to apply the assessment criteria in a

hierarchical manner. It must be made clear that once an assessment point has been missed, a

candidate cannot proceed beyond that mark boundary. For example, if a candidate misses

A4b then that candidate cannot proceed to the A6 criteria. However, if the candidate scored

at least two marks from A4a, A4c and A4d then a mark of 3 can be awarded. Failure to score

2 from the 3 would limit the candidate to a mark of 2 for skill A.

Centres are also reminded that they may be penalising their candidates by supplying a brief

which does not allow them access to the full range of marks. There is some evidence that

briefs which are either too prescriptive or too complex are limiting the achievement of both

able and weak candidates.

Whilst the appropriate use of ICT is to be encouraged as part of investigative work in science,

attention must also be given to its use in the presentation of the report. Spreadsheets have

been responsible for candidates receiving a penalty due to inconsistent use of significant

figures, both in raw and derived data sets. This, most often, is the result of ‘dropping’ the last

zero and is something a candidate should be aware of and be able to correct.

The use of graphic software has also been seen to present a number of potential traps for

candidates; for example, many graphs are too small. A computer generated graph should be

of a similar size to one drawn manually. Again, some software does not default to plotting

points. Large colourful diamonds appear popular, but this makes it difficult to read.

It is also obvious that much of the software used will fit a trend line using all the points in the

data set, including any anomalous points. Candidates should be able to manipulate the

software to avoid being penalised in this area of presentation. It is recommended that centres

advise candidates to produce an output which covers one side of A4 with points plotted as

‘dots’ or ‘crosses’ and to draw their line of best fit taking account of any anomalous points.

Furthermore, if readings are to be taken from the graph, e.g. for ∆x and ∆y, then gridlines

should be shown.

The advice which follows is intended to be more skill specific and addresses concerns raised

by moderators when suggesting an adjustment to the marks of a centre.

In skill A, candidates should be advised to include a specific statement regarding safety in

order to ensure the award of A2c. All that is required in most cases is a statement to the

effect that ‘normal laboratory safety measures were observed’ or ‘no specific safety issues

arose in this investigation’. Diagrams need to be clearly labelled and an indication of any

measurement to be made must be included in order to ensure the award of A4c.

In skill B, candidates should be advised as to the appropriate number of points required for a

graph and that a graph consisting only of two or three points is unlikely to score marks under

B4.

In skill C, candidates are in need of further guidance regarding graph titles and the labelling

of axes with both the correct quantity and units. When assessing skill area C, centres must

check the accuracy of the plotted points before awarding C4d. Moderators will check this and

Report on the Examination PhysicsA- Advanced

13

under the hierarchical scheme, failure to check by the centre can reduce the mark for skill C

from 8 to 3.

In skill D a majority of candidates score less than in skills A, B and C. The following points

are important. In D2 a comment on the spread of values in repeat readings or lack thereof. In

D4, the closeness of plotted points to the line of best fit when commenting on reliability. In

D6, a comment on the zero error of measuring instruments and a comment on why a straight

line graph fails to pass through the origin as predicted in the plan.

Unit 3: PA03/W : Current Electricity and Elastic Properties of Solids

General Comments

The examiners were very pleased with the response to this paper. Although the electricity

section questions were slightly more difficult than the corresponding questions in Summer

2001, candidates made a good effort at solving the numerical questions and also scored quite

heavily on the descriptive question on how to measure the Young modulus.

Many of the attempts at the calculations, although producing the correct answer, were very

untidy in presentation with successive equations seemingly being written in random areas on

the answer page. It was quite a relief to find a script where the candidate had performed a

calculation in consecutive steps which were presented on consecutive lines.

It appeared that there had been a significant effort in using correct units throughout.

Question 1

Most candidates scored well on this question, although part (a) proved to be the most

troublesome. A considerable number of candidates seemed unfamiliar with the effect of

shorting out, or connecting terminals together and many assumed that doing so would not

affect the effective overall resistance. In part (b) the large majority of candidates realised that

two of the resistors were in parallel and proceeded accordingly to obtain the correct answer.

There were very few errors in calculating the sum of the parallel resistors.

Question 2

Many of the silicon semiconductor diode characteristics presented in part (a) were poorly

drawn and the examiners felt that although the candidate knew what the characteristic looked

like, greater attention to detail and less sloppiness in drawing would have earned them many

more marks. The main errors were in drawing the forward characteristic as a continuous

smooth curve, without a sharp increase in current at 0.6 V or 0.7 V. In many cases the

increasing current would be represented as a vertical line, whereas in practice the slope of the

curve is large, but not infinite. In the reverse mode, the current would, very often, be shown

as slightly positive, which was not accepted. Other points to note in the reverse mode is that

the change to a large current at breakdown occurs sharply and then the curve may be drawn

as a vertical line. When values of voltage were given, they were usually correct.

Part (b) in general was not well answered. Many candidates wrote at length on how the

current varied with the voltage without once referring to the change in resistance, which was

the purpose of the question. The terminology of many candidates was confusing with

reference to ‘negative voltages in the forward mode’.

Question 3

Part (a) was a very straightforward question for 2 marks. The equation in part (i) was usually

correct, which is not surprising since it is given in the data sheet. A surprising number of

candidates failed to rearrange this equation in terms of VR.

Calculating the current in part (b)(i) was also straightforward and the majority of candidates

gained all the marks allocated. The calculation of the number of cells in part (ii) was

considered by the examiners to be reasonably difficult and they were well pleased by the

number of candidates who arrived at the correct answer, through a variety of methods.

Question 4

Answers to this question realised quite high marks. In part (a) the calculation of the total

resistance was invariably correct. Most candidates then realised that the three strips were in

parallel and proceeded accordingly. A significant number of candidates however, proceeded

by assuming that the resistance of the strip was 11 Ω and worked backwards through the

calculation. This method was not acceptable, since it was felt that the candidates had been set

a task to calculate the actual resistance of each strip from the total resistance of the element.

Very few difficulties arose in part (b), apart from several candidates taking the area of cross

section as circular. Many candidates used the approximate value of 11 Ω for the resistance of

each strip instead of 10.8 Ω, which they had obtained in part (a). This was not acceptable and

a penalty was applied.

Question 5

Part (a) produced all sorts of difficulties. Many candidates took the value of the current (5

mA) and multiplied it by √2 to give the peak voltage, being oblivious of the need to

incorporate the resistance in the calculation. Other candidates would simply write V = 10 V

with the examiner having no means of knowing if the candidate referred to the rms value or

the peak value. Although the relationship between rms and peak value is given in the data

sheet, some candidates used the wrong expression.

The oscilloscope trace in part (b) was, in general, very well drawn, with the waveform, peak

value (carried forward from part (a)) and period being correct, the period having being

correctly calculated.

Question 6

Almost all candidates gained reasonable marks on part (a)(i) even though some of the

descriptions were lacking in detail. Most of the diagrams were reasonably drawn with the aid

Report on the Examination PhysicsA- Advanced

15

of a ruler. Candidates who drew freehand usually produced inferior diagrams which failed to

gain all the available marks. A variety of methods were shown, usually two wires hanging

vertically, linked together by means of some vernier arrangement and a spirit level. Also

shown was a horizontal wire on a bench. Although this is not such an accurate method, it

was accepted but many candidates showed the mark on the wire as being about half way

along. This of course is only acceptable if the length of the wire is measured to that point,

but this was usually overlooked in the description. The least satisfactory method was

suspending a single wire with a ruler alongside although this did gain some marks. There

were an alarming number of diagrams which showed a completely unrelated length of wire, a

ruler, an isolated hook with a mass attached and a micrometer. Needless to say, such efforts

gained no marks.

In part (ii) candidates could have saved themselves considerable time and effort by reading

the question carefully and just listing the measurement they would make. Many candidates

listed the area of cross section as a measurement. This was not acceptable since area is a

derived quantity and it is the diameter which is measured. Many candidates also listed the

‘width’ of the wire, which again was not accepted.

The descriptions in part (iii) were, on the whole, quite reasonable, although most effort

seemed to go into describing how the length of the wire and its diameter were measured and

not giving sufficient attention to the experiment, i.e. measuring the extension for each mass

added and increasing the total mass to a certain value. There were very few references to

repeating the readings while unloading. This particular section of the question was also used

to award the quality of written communication marks and most candidates scored well on

this.

The descriptions in part (iv) of how to use the measurements to give the Young modulus was

reasonably done with about 50% of the candidates drawing a graph of force vs extension or

stress vs strain and using the gradient accordingly. Candidates who only used one set of

values to give one value of the Young modulus were not awarded all the available marks.

The calculation in part (b)(i) was performed satisfactorily, with the majority of candidates

calculating the correct extension for the steel wire. Marks were lost in part (ii) when the

answer was given without any reasoning.

Advanced Examination

This was the first time that examinations have been held for the Advanced Award in its

current form. The examinations which were available were those for Unit 4 on Waves, Fields

and Nuclear Energy and the five Option papers, Unit 5 to Unit 9.

Section A for each of the Option papers consisted of a common question on Nuclear

Instability. The topics covered in Section B of the five Option papers were, Astrophysics

(Unit 5), Medical Physics (Unit 6), Applied Physics (Unit 7), Turning Points in Physics (Unit

8) and Electronics (Unit 9).

There was a significant entry of approximately 3000 candidates for Unit 4 but only two

options, Units 5 and 8 had entries of over 100 candidates, the entry for the remaining options

being very low. With such a low entry, it is difficult to write a meaningful report on the

Option examinations.

Unit 4 : PA04 : Section A : Objective Test Questions

Objective test questions were an important section in the legacy ‘end-of-course’ A-level

examination but in that examination they covered the whole of the A-level syllabus. The

current objective test paper only covers the syllabus on Waves, Fields and Nuclear Energy.

There is therefore little to be gained by making any comparison between the current

examination and past objective test examinations.

For teachers who are not familiar with these form of questions, the important parameters in

the statistical analysis of each question are the facility, which is a measure of the percentage

of all candidates obtaining the correct answer and the point biserial index, which is a measure

of the discrimination produced by the question.

The fifteen multiple choice questions were chosen from a bank of questions all of which have

been pretested. Only those questions with a pre-examination facility of at least 30% and a

pre-examination point biserial index of at least 0.20 were considered for the examination.

The final choice of questions was made so that the objective test questions together with the

questions in Section B gave as full a coverage of the syllabus of Unit 4 as possible.

The keys to the objective test questions were:

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

The mean facility was 70% and the mean point biserial was 0.43

Questions 1 - 4 covered the ‘Oscillations and Waves’ section of the Unit. Each question

showed an increase in the facility over the pre-examination facility and in question 4 it

increased by more than 25% to a value of 74%. Question 2, on simple harmonic motion,

realised a very high discrimination of 0.60 with the weaker candidates opting for distractor A,

which gave zero acceleration at maximum displacement.

Questions 5 and 6 were set on Interference and Diffraction respectively and both questions

realised high facilities of over 70% with a good discrimination of greater than 0.5. The only

notable distractor was B in question 6 which gave the number of lines per metre on the

grating as 2 × 105 compared to the correct value of 5 × 10

5.

Question 7 had the distinction of being the only question on the paper in which the

examination facility of 50% was less than the pre-examination facility of 59%. It also had a

low discrimination of 0.37. The inference is that even the better candidates were not too

familiar with uniform motion in a vertical plane. The statistical analysis showed that the

three distractors were equally attractive to the candidates, who, to a large extent, were

obviously guessing at the correct answer.

Questions on gravitational potential energy have never been popular in objective tests so it

pleasant to report that in Question 8, candidates produced a facility of 72.5% for a numerical

calculation on this topic.

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Question 9 on the electric field between parallel plates caused no difficulty , but Question 10

on electric field strength and electric potential gave rise to some concern. The final facility of

42% in question 10 remained the same as the pre-examination facility, but the discrimination

of 0.18 was the lowest on the paper and showed a decrease from the pre-examination value of

0.29. Of the candidates, 21% thought that electric potential is a vector and 26% thought that

the potential gradient was not proportional to the electric field strength.

Questions 11 - 13 dealt with the section on ‘Magnetic Effect of Currents’ and all worked

well giving high facilities but with moderate discrimination of around 0.35.

There were two questions on ‘Nuclear Applications’; Question 14 on mass difference and

Question 15 on the purpose of a graphite moderator. Question 14 gave the highest facility in

the paper at 91% with question 15 not far behind at 87%. With such a high facility it was not

surprising that the discrimination was comparatively low at about 0.40.

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

General Comments

This test paper offered the first opportunity for candidates to show their knowledge and

understanding of the wide range of topics included within Unit 4. All candidates taking the

test would therefore do so after about only one term of study. Some well-prepared candidates

presented excellent answers to most of the questions, but in many scripts there was evidence

that candidates had attempted the test before they were fully conversant with the content of

the unit. Clearly one term of study can be adequate for able candidates to master this unit,

but some will take longer. These lower-achieving candidates may not have had enough time

to complete the unit or to consolidate their understanding.

In this examination paper, questions 5(b) and 4(b) were used for the purpose of assessing the

quality of written communication. Two marks can make an appreciable difference to the

overall performance of a candidate in a paper which has a maximum mark of thirty. When

answering questions which require prose it is therefore worth the candidates taking the

trouble to write in recognisable sentences that begin with capital letters, end with full stops

and show some understanding of the use of commas.

Transgressions over the use of significant figures were relatively few and occurred most

frequently in answers to question 2(b)(ii). Penalties involving missing or wrong units were

more common.

Candidates usually found questions 1, 3 and 5 to be the most rewarding. Question 2 was

often answered well, but sometimes left the candidates floundering. A large proportion of

candidates answered question 4 badly.

Question 1

The main problem in candidates’ answers to this question was confusion between single slit

diffraction and double slit interference. The completion of the sketch graph in part (a)

regularly gained full marks for the many candidates who appreciated its salient features.

Equally spaced markers on the horizontal axis were intended to guide candidates into

showing the subsidiary minima at equal spacing with the separation between consecutive

minima being half the width of the central maximum. Candidates who thought that the

separation between subsidiary minima was the same as the width of the central peak usually

achieved only half marks on this part. The relatively low intensity of all the subsidiary

maxima is not well known and no marking point was available for this aspect.

When marking part (b) the examiners viewed with great suspicion any answer which relied

on the Young’s slits equation, λ = (ws/D). The fact that narrowing the slit causes the pattern

to broaden was usually appreciated in part (i), but few candidates stated that the pattern is

also dimmer. In part (ii) many candidates had difficulty in deciding whether red light or

green light has the longer wavelength and the wrong choice, of course, caused many incorrect

answers to the way the separation of the maxima changes. The other point the candidates

could have made is that the colour of the pattern changes from red to green. It is worth

pointing out that the marks available for parts of questions are given in the question paper and

that these are intended to help candidates. In part (b), three marks were available and this

would indicate that a minimum of three points are required in a complete answer.

Question 2

The main failing in part (a) was thinking that k is mass per unit extension rather than force

per unit extension. Some candidates also used g = 10 N kg−1

, rather than the value of 9.81 N

kg−1

given in the Data Sheet and which should always be used unless candidates are

instructed to the contrary by the question. Choosing the correct unit for k was a recurring

problem.

In part (b)(i) many candidates doubled the value of k determined in part (a) and thus appeared

to think that the two springs in series would be twice as hard to extend as a single spring.

More thorough understanding would indicate that the same force must produce double the

extension when pulling on a specimen that is twice as long, so k must halve. The incorrect

value of k was allowed as a consequential error in part (ii) and the equation for the period was

normally applied successfully, but when converting to oscillations per minute, the period was

sometimes wrongly multiplied by 60.

Question 3

More careful reading of the question would have produced a greater number of satisfactory

answers to the sketch graph in part (a). Most candidates realised that a straight line from the

origin was needed, but many lines were continued beyond the point 4.5 V, 9.0 µC. Almost

inevitably, some of the lines were drawn as exponential curves.

‘Derivation of’ seems to be an unwelcome term in the new Specification, for very few

candidates were able to produce a completely satisfactory answer to part (b)(i), which

required them to show that E = ½QV. Whilst most candidates could identify energy stored

with the area under the graph, only a tiny minority could link energy stored with work done

by the charging source, or explain ∆W = V∆Q. Consequently it was usual to award only one

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19

mark out of the three available for part (i). Answers to part (b)(ii) were usually correct with

many candidates sensibly choosing to approach the calculation via ½CV2.

Question 4

Many of the attempts to answer this question showed a complete lack of understanding of

forces in electric fields and much confusion between magnetic fields and electric fields.

Taken as a whole, the question proved to be an excellent discriminator of the proficient

physics student.

Perhaps it is understandable that many candidates wrongly chose ‘to the left’ in part (a)(i) and

therefore followed it with ‘deceleration’ in part (ii). It is much more difficult to appreciate

why the electron might be considered to follow a curved or circular path in part (a) - as stated

by some candidates. The parabolic path in part (b) was often shown curving downwards.

Part (b)(ii) required an explanation based on an understanding of projectile motion. Quite a

large number of candidates preferred to refer to Fleming’s left hand rule!

Question 5

The principal features of the binding energy per nucleon curve in part (a) were usually well

known. The main failing was to show an excessively large fall to the right of the maximum.

In practice, the binding energy per nucleon values decrease only from about 8.5 MeV to about

7.5 MeV.

Part (b) revealed common misunderstandings about the nature of binding energy. Treating

binding energy as something a nucleus possesses, rather than energy that a nucleus loses, is

particularly unhelpful. A large proportion of the attempts to answer part (b)(i) failed to gain

any marks because the candidates did not refer to fission and fusion as processes involving

nuclei. They preferred to talk about splitting atoms or joining nuclides, or (even) nucleons.

Use of correct terminology is essential in this area. Those candidates who had a good

understanding of nuclear energy were able to explain that both the fusion and the fission

processes are accompanied by an increase in the binding energy per nucleon, which is the

source of energy that is released. The mark scheme adopted for part (b) was fairy generous

and those candidates who had a clear understanding of the principles were usually rewarded

with all three marks.

Units 5 - 9 : PHAP : Practical

General comments

The majority of the entry of nearly 200 candidates came from just two centres. The

candidates were generally able to demonstrate better qualities of understanding and written

communication than those seen in PHA3/P. Their extra experience and maturity was tested

by both questions. The prediction made in the report on PHA3/P for Summer 2001, that

candidates would get better at meeting the demands of AO3(a) but in turn could be expected

to be confronted by more testing questions involving AO3(b), (c) and (d) was borne out here.

The overall mark distributions for the January PHA3/P and PHAP examinations were quite

similar but although PHAP candidates found question 1 more accessible, any improvement

was offset by the more discriminating nature of question 2.

Both questions were completed in all scripts seen, indicating that candidates had sufficient

time but there was significantly less use made of supplementary answer sheets than in

PHA3/P. Hopefully this indicates that candidates are becoming conscious of the need to deal

with question 1 in as concise a manner as possible. It was certainly easier to follow the

thread of argument contained in most answers than was the case in PHA3/P.

Candidates should be reminded that they must justify statements if they are to gain full credit

for their answers. Many candidates wrote , in question 1, that they would keep the power

output of the spotlamp constant but neither diagram or text showed the means to do this.

Likewise, in question 2, some claimed to have repeated micrometer measurements to

determine the diameter of the vibrating wire but their scripts failed to provide evidence that

this had been done.

One aspect of the answers to question 1 that was disappointing was the (typically) incomplete

explanation given about how graphs could be used to settle the argument on how the

illumination of the spotlamp varied with distance. Many candidates went as far as proposing

suitable graphs to plot but then made vague statements such as ‘see if a straight line is

produced’ about how to test a particular theory. A test of direct proportionality between

variables involves checking if the best-fit line passes through the origin.

In question 2 the tabulation of results sometimes lacked consistency and there were many

scripts in which the mass per unit length of the wire was given without a unit. The most

wasteful error seen in a large number of scripts was neglecting to make adequate use of the

range of masses available.

The impression gained was that many candidates worked hard to produce answers to question

1 to maximise their mark, but then, in many cases, they underestimated their demands of

question 2. Only 30% gained 15 or more marks in question 2 out of the 22 marks available.

(The equivalent figure in PHA3/P was over 50%).

Question 1

Candidates were required to design an experiment to test which of two theories concerning

the way that the intensity of a spotlamp varies with distance from the lamp.

Most candidates illustrated their answer with a diagram with suitable labelling of the distance

between the lamp and the LDR. Other diagram rarely earned full credit. Many candidates

gave schematic views that failed to show whether a suitable working arrangement had been

given. Even when correct circuits were drawn the symbol used for the LDR was generally

wrong. Some accounts included spurious detail in the LDR circuit such as a series resistor.

Other diagrams gave a voltmeter and/or ammeter wrongly connected or used a single circuit

to supply both the LDR and spotlamp. Candidates who showed an ohmmeter often

incorrectly included a power supply in the circuit. Very few diagrams were drawn to support

the statement, usually given later, that the power output of the spotlamp was maintained at a

constant level.

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Thereafter, progress was generally better with most describing a sensible procedure to find

the resistance of the LDR at different distances from the spotlamp. Some saw the calibration

graph as evidence that the resistance was directly proportional to the illumination but a

significant proportion correctly explained that they could incorporate the resistance values

with the graph to find the illumination at certain distances from the spotlamp.

Most candidates recognised that to resolve the argument about whether the variation of

illumination followed an inverse-square or exponential pattern, a graph should be drawn.

However the use to which the graph would be put was not usually specified correctly and

bland statements about ‘straight line’ or ‘linear’ graphs were not accepted.

Many candidates stated suitable control measures for the experiment could include using

black-out or enclosing the apparatus in a light-proof tube: provided suitable reasoning was

given this was accepted. Keeping the power output of the spotlamp constant was another

acceptable answer but once again, justification of why and how this was to be done was

expected. Some candidates thought that a parallel could be drawn with radioactivity

measurement and stated that a background light level could be measured beforehand to be

subtracted from the measured illumination.

Discussion of potential difficulties and how these were overcome tended to be blanket

statements about ‘repeating and averaging’ measurements and if reasoning was attached this

was often ‘to improve accuracy’. Many candidates stated that their objective was to obtain

‘reliable data’: the use of bland unconvincing jargon does not inspire confidence and is

unlikely to gain credit. No candidates thought to discuss how the distribution of data might

be varied to improve the definition of the graph, but many wrote about the need to repeat

readings to improve accuracy. Candidates should understand that repeating and averaging

only reduces random error, thus improving precision but accuracy is improved only when

systematic error is reduced.

It should not, however, be assumed that all candidates are incapable of writing carefully and

sensibly about their ideas. There were many good accounts and about 25% earned at least 6

out of the possible 8 marks. This compares with only 10% at PHA3/P.

Question 2

Candidates were required to investigate the forced vibration of a wire in a magnetic field.

This question discriminated well, although the suspicion exists that carelessness may have

contributed in some cases to fewer marks than might be expected at the upper end of the

range. Candidates must take care to accumulate marks in all parts of these questions if they

are to maximise their chances. Carelessness affected all parts of some candidates’ answers,

starting in (a) where some failed to repeat micrometer measurements or failed to supply a unit

with their answer. Most candidates, however were able to identify the SWG number of the

wire.

There is considerable variation in the standard of and approaches to tabulation of data and

this leads in some cases to confusion and inconsistencies. Units are appearing alongside data

in the table rather than in the column headings. Candidates need to plan the layout before

they set pen to paper so that measured and derived data can be arranged in logical and

accessible fashion, ideally in a single table (and definitely not in separate sets). It is

suggested that candidates adopt the solidus notation between the quantity and unit in the

column headings for tables and for the marking of graph axes: thus m /kg½ is correct. It is

also expected at this level that candidates do not use solidus notation when unit symbols are

combined in a quotient: thus

µ = 0.93 × 10−3

kg m−1

is correct. Candidates should also understand that poor or

inconsistent tabulation of data will be penalised in the same way that poorly-marked points or

line on a graph attract the deduction of marks.

Candidates were given a mass hanger and slotted masses to provide a total of at least 400 g

but many used a restricted range or incorrectly recorded the mass without taking account of

the hanger. Others used a total of five different masses instead of five in addition to the

initial set. The consistent use of significant figures in the recording of data was sporadic,

some recording the length of wire between the bridges to cm while others gave m to only 2

significant figures. Others simply lost a mark through inconsistent recording of data.

Providing six points were plotted, most were able to draw a best-fit line that passed close to at

least five points, thus earning the available mark for quality.

It was rare to find the correct unit given with m on the horizontal axis of the graph and the

scaling marks were usually determined by whether the candidate had chosen to include the

origin. Most candidates appreciated the need to choose scales that maximise the use of the

page but they should be discouraged from using difficult scales that make interpretation

difficult. The accuracy with which the points were plotted is also checked and instances were

found where these did not tally with the tabulated data.

It seems to be well known that a large y-step and x-step are expected for gradient

calculations. It helps significantly to see the triangle drawn below the best-fit line on the

grid. There are still some candidates that fail to provide evidence to show how they calculate

the gradient of their graph. Careful working was usually found to produce numerical results

for µ that were satisfactory but units were often missing.

In the explanation (e)(i) some candidates misread the question and talked about measures to

reduce uncertainty in the length l rather than in the diameter d. In (e)(ii) most candidates got

as far as recognising that an increase in SWG number reduced the diameter but few explained

the impact on µ and hence on the gradient of the graph. In (e)(iii) almost all candidates stated

that the two-loop mode of oscillation would require the length of wire between the bridges to

be twice that of a single loop.

Units 5 - 9 : PHAC : Coursework

Less than two hundred candidates were presented for the A2 coursework examinations and

the comments are therefore made on the basis of a relatively small number of scripts seen.

The general comments on the presentation of coursework are the same as those made on the

AS work and the reader is thus referred to the detailed comments which appear on pages 13

and 14 of this report.

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Units 5 - 9 : PHA5/W - PHA9/W : Section A : Nuclear Instability

The question on nuclear instability realised some good responses but part (a)(i) was not

always answered as well as one would have hoped. Candidates were aware that an electron

was captured by a proton which then became a neutron, but the answers were not specific

enough as to where the electron came from. Statements such as ‘an electron is captured’

were not sufficient to gain the mark. It needed to be made clear that it was an orbiting

electron. Answers to part (a)(ii) were sometimes vague, with only about 50 % of the

candidates realising that electron capture excites the daughter nuclide. The equation in part

(iii) usually gained some marks and it was good to see that only rarely was an anti positron or

anti electron inserted in the equation.

Part (b) realised very good marks and a significant number of candidates were awarded the

maximum of five. The conversion from hours into seconds was usually performed correctly

in part (i) to give the required result. Part (ii) likewise gave good results although it was here

that problems with significant figures became apparent. There was no real difficulty with

part (iii), candidates using ∆N/∆t correctly.

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

Question 2

There is normally one optics question on this paper and, in general, question 2, which dealt

with the converging lens, was answer very well. The majority of candidates were aware in

part (i) that the image was virtual. In part (ii) calculating the focal length from the power of

the lens proved to be straightforward, although a disappointing number of candidates

attempted to calculate it using the lens formula.

The difficulty encountered by candidates in part (iii) was failing to identify that the sign of

the image distance was negative in the lens equation. However, a majority of candidates

obtained the correct answer for the object distance. Finally, in part (iv), the majority of

candidates drew the correct ray diagram, although there were a significant number who did

not recognise the situation as being that of a magnifying glass. Many candidates labelled the

principal foci as focal lengths, showing a lack of understanding in this field.

Question 3

In part (a)(i) drawing a diffraction pattern of concentric circles would appear to be

straightforward, but a significant number of candidates drew the bands as single lines,

without showing any width to them. This aspect of the diffraction pattern needs to be

stressed to candidates. Stating the ‘Rayleigh criterion’ for the resolution of two stars was

answered well, with the majority of candidates using two intensity distributions to illustrate

their answers.

The calculation of the minimum diameter of the telescope in part (b) was also correctly

performed by most candidates, although there were several attempts where , after giving the

correct equation, the parameters were inverted when values were inserted in the equation.

Carelessness of this nature can cause a significant penalty in a paper where there are only

forty marks available.

Question 4

Questions on the Hertzsprung - Russell diagram have always proved to be popular with

candidates and this question was no exception. Drawing the regions of the different types of

stars on the diagram was usually done correctly, but some attention needs to be given to the

correct shape of the main sequence band, in particular to the mid-region where the band

levels off slightly.

Some of the definitions of apparent magnitude in part (b)(i) were slightly vague, e.g. ‘how

bright the star appears to be’. Candidates should make clear that it is the brightness as seen

from Earth. Both calculations were performed satisfactorily. Many answers to part (iv)

lacked detail, with candidates simply reiterating the information given in the question without

attempting an explanation. In order to be awarded all the marks for this section candidates

needed to relate the strong Balmer series to the correct spectral class. Part (c) provided many

correct answers although a considerable number of candidates included all four stars in their

answers.

Question 5

In general, this question was not well answered. Only a minority of candidates were aware,

in part (a), that quasars were discovered as strong radio sources. The type of calculations in

part (b) are familiar to candidates and this part yielded the best answers. Many candidates

however used the incorrect value of λ in the Doppler equation, using the value in the

spectrum of the quasar rather than the value measured in the laboratory. The most common

error in calculating the distance to the quasar was one of units, many candidates having to

manipulate their calculations in order to obtain the value quoted in the question.

Answers to part (c) were slightly disappointing. Very few candidates used the inverse square

law correctly to estimate the power output of the quasar. The most common attempt was to

simply used the ratio of the distances. Many of the candidates who did give the correct form

of the inverse square law failed with the subsequent calculation. Part (ii) provided candidates

with an opportunity to write at length without focussing on the main areas of controversy

concerning quasars. A common error was the use of energy or brightness rather than the very

large power output, when commenting on this property of quasars.

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

The following comments on the responses to this paper must be taken in the context of a very

small entry.

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Question 2

Although nearly all candidates were able to give two uses of lasers in part (a), comparatively

few were able to give relevant details of the method of application in part (b). The answers to

the method of application usually consisted of vague statements such as ‘applied direct to

point’ without describing how it was applied. The answers to the safety features were much

better with nearly all candidates being able to give at least one.

Question 3

In part (a) most candidates were awarded the allocated two marks, but occasionally the use of

vague statements such as ‘using gel’ failed to gain a mark. Part (b) was poorly answered with

very few candidates being aware that the properties of the amplifier required to enhance the

ECG signal were low noise, high gain and high input impedance.

Most candidates sketched the correct waveform in part (c), but some gave the waveform for a

heart muscle. However, the scales on the potential axis were inaccurate with many going

from –70 mV to +30 mV and some candidates obviously guessing as to the location of zero

potential. The labelling of the actual waveform was accurately done by most candidates.

Question 4

This was the best answered question on the paper with many responses gaining full marks.

The main problems which arose were that answers such as ‘uneven eye’ were too vague to be

awarded the mark in part (i). In part (ii) candidates failed to stress that there were two image

planes involved and gave answers such as ‘blurred image’.

Nearly all the candidates gave the correct answer to part (iii). In part (iv) all the candidates

were able to give ‘power’ as one quantity, but few were able to give the ‘angle of orientation’

as the other.

Question 5

Answers to part(a) were generally poor with few candidates being awarded both marks. Part

(b) was very poorly answered with most candidates making meaningless comments or

statements which were too vague to be awarded any marks.

The common error in part (c) was using the reading of 94 dB as the intensity, rather than as

the intensity level. Of those candidates who used this value correctly, about 50% were unable

to rearrange the equation correctly to obtain the final answer. Similarly in part (d) few

candidates were able to calculate the final intensity correctly, the main problem again being

the incorrect use of data in the equation.

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

General Comments

As with unit 6 only a small number of centres entered candidates for this option and the

comments on the responses to the paper must be interpreted in the context of a small sample.

The majority of candidates made a serious attempt at every question, no blank scripts were

received and almost all candidates completed most of the paper. The final part of question 5

was occasionally omitted or attempted only perfunctorily, but it is difficult to be sure with a

small sample whether this was a result of shortage of time or ignorance; good candidates

appeared to find the time adequate.

The style and demands of the questions in this option are very similar to those which

appeared in the Applied Physics Module in the previous, and now defunct, A-level

examination. Not surprisingly the scripts seen this time showed similar strengths and

weaknesses to scripts seen in those examinations. Many candidates incurred the unit penalty,

usually for using the wrong unit rather than omitting the unit. Significant figure errors were

far less frequent. The level of competence in the Quality of Written Communication was

poor throughout.

Question 2

Part (a) was not answered well, with many zero scores and very few candidates gaining full

marks. The symbol W was usually identified as work, but some candidates thought that either

Q or U identified temperature. Of the candidates who could identify the symbols correctly,

the majority provided answers of the form ‘∆Q is a change of heat, ∆U is a change of internal

energy and ∆W is a change of work’; these answers were not awarded any marks.

Candidates at this level are expected to recognise that words such as change, alter and vary

are too imprecise to be used safely in answering a physics question. The few candidates who

did recognise this, correctly identified ∆Q as the energy supplied to the gas, ∆U as the

increase in internal energy and ∆W as the work done by the gas.

Most candidates scored some marks on part (b), either two marks for one of the processes or

four marks for both processes. The isothermal process appeared to be the more difficult of

the two processes on which to gain marks. Some candidates clearly did not link this exercise

to the equation given in part (a).

Question 3

Most candidates correctly calculated the moment of inertia of the rotor in part (a)(i), but

many did not know its unit. In section (ii), the conversion from rev min−1

to rad s−1

was often

not carried out or calculated incorrectly.

Part (b)(i) was answered correctly by most candidates, although again the unit of torque was

largely unknown or omitted. In part (ii) few candidates used the relation loss of kinetic

energy = average power × time and there were very few correct answers.

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27

Almost all candidates attempted unsuccessfully to use equations of uniformly accelerated

motion to answer part (c). Candidates who recognised that kinetic energy change was

involved arrived at the correct answer.

Question 4

Most candidates answered part (a) correctly and many were awarded full marks.

Part (b)(i)was also answered well with mostly correct answers. The most common answers

for part (b)(ii) took the forms ‘because an efficiency equal to 1 makes it 100% efficient and

this is not possible’, ‘because of heat loss’ and ‘friction’. Few candidates could explain

satisfactorily why the efficiency is less than 1; most offered several suggestions, all of which

were vague and usually expressed in a single rambling phrase with no capital letter, no

commas and no full stop.

Question 5

Most candidates took the hint in the question and used conservation of angular momentum to

calculate correctly the speed of the wheel in part (a). All the candidates who made any

serious attempt at part (b) tried to use an equation of uniformly accelerated motion in part (i),

often appropriately but usually with an incorrect value of angle (most commonly θ = 0.49

m). The equation T = Iα was used in part (ii) to calculate a torque, but few could extend this

to work out the corresponding force.

Unit 8 : PHA8/W : Section B : Turning Points in Physics Option

Question 2

In part (a) almost all the candidates were aware that an electromagnetic wave consists of an

electric wave at right angles to a magnetic wave and that the two waves are in phase. A

significant number of candidates failed to indicate the direction of propagation of the wave.

Part (b) proved to be more difficult and only a small number of candidates knew that the

change in magnetic field or magnetic flux through the loop produced the induced emf.

Again, very few candidates were aware, in part (ii), that the waves are polarised, although

some candidates did realise that the magnetic wave would not produce an induced emf when

in the same plane as the loop. There were a few candidates who claimed that the action of

rotating the loop polarised the waves from the transmitter.

Question 3

Answers to part (a) of this question were, in general, quite poor. Very few candidates

realised that the mass of an object increases when its speed increases and even fewer

recognised that as the speed of an object approaches the speed of light, that the mass

increases at a greater rate. The not uncommon erroneous line of reasoning found in the

answers commenced with the classical formula for kinetic energy, then invoking the speed of

light as the maximum possible speed, using E = mc2 to claim that the mass could increase

therefore that the classical kinetic energy could increase even though the speed is limited.

The calculations in part (b) were carried out reasonably well with most candidates being able

to show in part (i) that the kinetic energy was 3.4 ×10−19

J. In part (ii) many candidates were

able to calculate the mass increase due to this kinetic energy, but very few remembered to

add the rest mass to their mass gain.

Responses to part (c) were disappointing because very few candidates knew how to proceed

correctly. Many candidates used the classical expression for kinetic energy, inserted the

value for kinetic energy obtained in part (b) and used 23m0 as the mass. The examiners are of

the opinion that candidates would benefit from being shown how the classical expression for

kinetic energy is derived from E = mc2 when v << c.

Question 4.

The majority of candidates gained high marks for this question. Part (a) was quite

straightforward and most candidates calculated the correct speed of the droplet. Again, in

part (b) a significant number of candidates scored the maximum possible marks with a clear

and correct derivation of the equation for the radius, followed by a correct calculation.

In part (c) many candidates were able to calculate the mass of the droplet correctly and then

proceeded to calculate the charge. A significant number of candidates did obtain the correct

value for the charge by equating the electric force to the viscous force and using the value of

speed obtained in part (a). Most of these candidates, however, lost a mark by not explaining

why the viscous force could be substituted for the weight of the droplet.

Question 5

In part (a)(i) many correct calculations for the speed of the electrons were seen, but some

candidates omitted the unit of speed. Most of the candidates who used the value of the speed

from part (i) to calculate the wavelength in part (ii) did so correctly, but those who chose to

calculate the wavelength directly from the pd did so incorrectly. The reason for this was that

the symbol for pd in the equation was thought to represent the speed, or else the charge of the

electron was omitted from the calculation.

The majority of candidates correctly stated in part (b) that the resolution would be increased

and then gave a correct explanation. However a significant number considered that the

magnification, rather than the resolution, would be increased. Very few candidates realised

that the image would be brighter.

Report on the Examination PhysicsA- Advanced

29

Unit 9 : PHA9/W : Section B : Electronics Option

Question 2

In part (a) most candidates calculated the correct value for the current in the circuit, having

first correctly deduced the correct voltage across the resistor. It was therefore surprising to

find that few candidates obtained the correct value for the minimum possible value of R in

part (ii). The recurring error here was that having found the maximum current through the

diode, they would then find the resistance of the diode and not the resistor.

Responses to part (b) were disappointing. Very few candidates showed a correctly rectified

waveform, but it was pleasant to find some sketches with the positive wave being clipped at

6.8 V. Very few candidates showed the negative waveform clipped at 0.7 V. Several

candidates failed to show the correct period on the waveform even though they had calculated

it correctly.

Question 3

The examiners were well pleased with the responses to part (a). In part (i) the growth and

decay of Vout was drawn reasonably well, except that some candidates did not realise that the

capacitor had fully charged (or discharged) before the end of the input pulse and so did not

draw a small horizontal section at 6.0 V or zero volts. The curves were drawn so that Vout

reached its maximum value at the same instant as the pulse ended. Likewise with the decay

curve. The correct calculation of the time constant in part (ii) gave the candidates a clue as to

the form of the curves required in part (iii). Most candidates realised that the capacitor would

neither charge or discharge fully in the available time and thus tended to draw the correct

form of the waveform except that it would usually have a maximum value of 6.0 V and a

minimum value of zero volts. Very few candidates drew the waveform in between values

which lay between these two values.

Part (b) gave the candidates a chance to give an explanation of the waveforms drawn in part

(a) and most of them gave a fairly comprehensive discussion in terms of the relative time

constants of the two waveforms.

Question 4

Answers to part (a)(i) were fairly disappointing in that candidates explained negative

feedback in terms of the output being fed back into the negative input, without stating that the

output voltage was 180o out of phase with the input voltage. The advantages of using

negative feedback in an amplifier were well known.

In part (b) most candidates did not notice that there was a simple relationship between R1, R2

and Rf resulting in a simple equation giving Vout in terms of V1 and V2. The method adopted

was to calculate the value of Vout each time. When drawing the form of Vout, some candidates

did not include the negative factor and gave Vout as being positive. The other error which

occurred was that the maximum value of Vout was given as 15 V, not realising that it saturated

at 12 V.

Question 5

This question produced high marks. Very few candidates failed to draw the diodes the correct

way and in part (b) the majority argued correctly in terms of maximum forward current and

peak reverse voltage that diode C should be used in the circuit.

Report on the Examination Physics A – Advanced

31

Mark Ranges and Award of Grades

Unit/Component

Maximum

Mark

(Raw)

Maximum

Mark

(Scaled)

Mean

Mark

(Scaled)

Standard

Deviation

(Scaled)

PAO1 – Particles, Radiation and

Quantum Phenomena60 60 38.6 12.5

PAO2 – Mechanics and Molecular

Kinetic Theory60 60 30.7 12.0

PA3P – Current Electricity andElastic Properties of Solids

Practical80 80 51.2 11.0

PA3C – Current Electricity and

Elastic Properties of Solids

Coursework

80 80 50.4 12.3

PAO4 – Waves, Fields and Nuclear

Energy60 60 35.3 11.0

PA5P –Astrophysics Practical 90 90 56.0 18.1

PA5C –Astrophysics Coursework 90 90 52.4 15.2

PA6P – Medical Physics Practical 90 90 - -

PA6C – Medical Physics

Coursework90 90 52.7 13.4

PA7P – Applied Physics Practical 90 90 44.2 11.3

PA7C – Applied Physics

Coursework90 90 58.9 14.4

PA8P – Turning Points in PhysicsPractical

90 90 48.4 14.0

PA8C – Turning Points in Physics

Coursework90 90 54.2 16.1

PA9P – Electronics Practical 90 90 58.7 12.6

PA9C – Electronics Coursework 90 90 - -

For units which contain only one component, scaled marks are the same as raw marks.

PAO1 Particles, Radiation and Quantum Phenomena

(3115 candidates)

GradeMax.

markA B C D E

Scaled Boundary Mark 60 48 42 36 31 26

Uniform Boundary Mark 90 72 63 54 45 36

Physics A - Advanced Report on the Examination

32

PAO2 Mechanics and Molecular Kinetic Theory

(2511 candidates)

GradeMax.

markA B C D E

Scaled Boundary Mark 60 39 34 29 24 20

Uniform Boundary Mark 90 72 63 54 45 36

PA3P Current Electricity and Elastic Properties of Solids

Practical (298 candidates)

GradeMax.

markA B C D E

Scaled Boundary Mark 80 61 54 47 41 35

Uniform Boundary Mark 120 96 84 72 60 48

PA3C Current Electricity and Elastic Properties of Solids

Coursework (580 candidates)

GradeMax.

markA B C D E

Scaled Boundary Mark 80 64 56 48 41 34

Uniform Boundary Mark 120 96 84 72 60 48

PAO4 Waves, Fields and Nuclear Energy

(3014 candidates)

GradeMax.mark

A B C D E

Scaled Boundary Mark 60 45 39 34 29 24

Uniform Boundary Mark 90 72 63 54 45 36

Report on the Examination Physics A - Advanced

33

PA5P Astrophysics Practical

(38 candidates)

GradeMax.

markA B C D E

Scaled Boundary Mark 90 65 58 51 44 37

Uniform Boundary Mark 90 72 63 54 45 36

PA5C Astrophysics Coursework

(102 candidates)

GradeMax.

markA B C D E

Scaled Boundary Mark 90 69 61 53 45 37

Uniform Boundary Mark 90 72 63 54 45 36

PA6P Medical Physics Practical

(no candidates)

PA6C Medical Physics Coursework

(25 candidates)

GradeMax.mark

A B C D E

Scaled Boundary Mark 90 67 59 51 44 37

Uniform Boundary Mark 90 72 63 54 45 36

PA7P Applied Physics Practical

(9 candidates)

GradeMax.

markA B C D E

Scaled Boundary Mark 90 63 56 49 43 37

Uniform Boundary Mark 90 72 63 54 45 36

Physics A - Advanced Report on the Examination

34

PA7C Applied Physics Coursework

(8 candidates)

GradeMax.

markA B C D E

Scaled Boundary Mark 90 67 59 51 44 37

Uniform Boundary Mark 90 72 63 54 45 36

PA8P Turning Points in Physics Practical

(136 candidates)

GradeMax.

markA B C D E

Scaled Boundary Mark 90 63 56 49 43 37

Uniform Boundary Mark 90 72 63 54 45 36

PA8C Turning Points in Physics Coursework

(54 candidates)

GradeMax.mark

A B C D E

Scaled Boundary Mark 90 67 59 51 44 37

Uniform Boundary Mark 90 72 63 54 45 36

PA9P Electronics Practical

(14 candidates)

GradeMax.

markA B C D E

Scaled Boundary Mark 90 65 58 52 46 40

Uniform 90 72 63 54 45 37

Report on the Examination Physics A - Advanced

35

PA9C Electronics Coursework

(no candidates)

Advanced Subsidiary award

Provisional statistics for the award (421 candidates)

A B C D E

Cumulative % 21.14 40.62 65.32 81.00 92.16

Definitions

Boundary Mark: the minimum (scaled) mark required by a candidate to qualify for a given grade.

Mean Mark: is the sum of all candidates’ marks divided by the number of candidates. In order to

compare mean marks for different components, the mean mark (scaled) should be expressed as a

percentage of the maximum mark (scaled).

Standard Deviation: a measure of the spread of candidates’ marks. In most components,

approximately two-thirds of all candidates lie in a range of plus or minus one standard deviation from

the mean, and approximately 95% of all candidates lie in a range of plus or minus two standard

deviations from the mean. In order to compare the standard deviations for different components, the

standard deviation (scaled) should be expressed as a percentage of the maximum mark (scaled).

Uniform Mark: a score on a standard scale which indicates a candidate’s performance. The lowest

uniform mark for grade A is always 80% of the maximum uniform mark for the unit, similarly grade

B is 70%, grade C is 60%, grade D is 50% and grade E is 40%. A candidate’s total scaled mark for

each unit is converted to a uniform mark and the uniform marks for the units which count towards the

AS or A-level qualification are added in order to determine the candidate’s overall grade.