Mark Scheme with Examiners

Mark Scheme with Examiners’ Report IGCSE Physics (4420)

June 2006 delivered locally, recognised globally

Mark Scheme with Examiners’ Report

June 2006 All the material in this publication is copyright © Edexcel Limited 2006

PHYSICS 4420, MARK SCHEME Abbreviations used in mark schemes: OWTTE - or words to that effect dop - depending on previous ecf - error carried forward ora - or reverse argument sfs - start from scratch UP - unit penalty Paper 1F Question 1 Answer(s)

Extra information

Mark(s)

(a)(i) (ii)

arrows unlike poles attract

(b)(i)

needle drawing pin

1 1

same as before

1

(ii) (c)

opposite poles attract/ they attract

correct shape correct direction shown by arrow touches the magnet twice

whether part or whole

1 1

1 1 1 Total 8 marks

Question 2 (a)(i) (ii) (iii) (iv) (b)(i) (ii)

R Q two longitudinal sound hertz 20 /4 = 5 no UP

1 1 1 1 1 kHz

c/s

1 1 1 Total 8 marks

Question 3 (a)(i) (ii)

(b)(i)

A 1. the temp of 50ºC in A must be the wall heater 2. heat moving straight up from the floor in B ANY TWO less draught warmer at floor level most of person’s time at floor level

1 1 1

1 1 Total 5 marks

Question 4 Answer(s)

Extra information

Mark(s)

binary one zero analogue digital analogue

1 1 1 1 1 1 Total 6 marks

Question 5 (a)

conserved

same on both sides

(b)

10 implies 100 - 90

2

(c)(i)

Efficiency = Useful energy output / total energy output

1

(ii)

No less of the energy goes for the intended purpose OWTTE

1 1

1

Total 6 marks Question 6 (a)

kinetic electrical

(b)

coal

(c)

gas work doing work watt

1 1 accept alternatives but not with the word ‘oil’ included supply or transfer of energy

1 1 1 1 1


perspex polythene

1 1

(b)

friction

1

Answer(s) (c)(i) (ii)

(d)(i) (ii)

Extra information

Mark(s )

rod cloth

1

electrons are negative when they move away they leave a positive charge

1 1

spark between tank and nozzle could start an explosion

1 1

connect the tank and the nozzle

earth both

1 Total 9 marks

Question 8 (a)

(b)

Gas particles far apart moving in all directions Solid particles close together moving to and fro

1 1 1 1

boiling evaporation

1 1 Total 6 marks

Question 9 (a)

all four correct (3) or any two correct (2) or any one correct (1) do not credit lines connected to any box with two (or more) lines to/from

3

Answer(s)

Extra information

Mark(s)

(b) all four correct (3) or any two correct (2) or any one correct (1) do not credit lines connected to any box with two (or more) lines to/from

3


brass

accept ‘metal’ or any reasonable choice of a named metal e.g iron or steel but not for example ‘gold’, sodium’, ‘platinum’,etc

1

(b)(i)

green and yellow

both but in either order

1

(the metal case of) the iron

appliance / metal

1

(c)

to prevent the user getting a shock/ electrocution

to carry current to the earth / the groun there is a fault / loose connection / wire (in the iron) or so current does not go through pers

1

(d)

use of insulated/ plastic casing/cover/correct place dop No need for earth (wire) / use 2-wire electrical parts can not be touched less/no chance of shock

(ii)

1 1 1

Total 7 marks Question 11 (a)(i)

centre of X along the vertical line

1

within logo, +/- 1 mm horizontally (ii)

B A C

All correct (2) Any correct (1)

2

(iii)

Air resistance

Drag or air friction

1

Answer(s) Extra information (b)(i) (ii)

Mark(s)

Answer(s)

Slope/gradient (of the line)

Line increasing / line going up

1

500 (m) (2)

or any clear indication, on the graph or elsewhere, that the distance is represented by (some of) the area under the graph (1) e.g. ½ (20 × 30) = 300 incorrect use of s = ut + ½ at2 scores 1

2

Total 7 marks Question 12 (a)(i) (ii) (iii)

Reflected 3.5 (s) 1155 (m) ecf

(b)

Frequency (of the echo)

Do not accept ‘bounced’ or echoed’ or 330 x 3.5 (1) may ecf from (a)(ii) or sfs Or loudness / volume / amplitude Not sound of the echo Allow ‘shorter delay’ (2)

1 1 2

2 Total 6 marks

Question 13 (a)

conduction and convection

(b)

silver(ed surface)

(c)

both either order

1 2

reflects (radiant) (heat) / infra red radiation (back into flask) / contents dop

or is a poor emitter or absorber (of radiation/infra red)

(metal) better (heat) conductor

or poorer (heat) insulator

(so contents) will cool more quickly / lose heat

or not keep warm for long do not credit just ‘will not keep warm’

casing becomes hot

accept argument based on cold contents

max 2

Total 5 marks


Extra information

(a)

0.025 (m2)

Or 0.25 x 0.1 (1) 10 x 25 (1)

2

(b)(i)

pressure = force ÷ area

Or p = F ÷ A Or any transposed version

1

4800 (Pa) (2)

or 4.8 kPa (2) or 120 ÷ 0.025 (1) may ecf from (a) or sfs

2

(ii)

Mark(s)

Total 5 marks Question 15 (a)(i) (ii)

Direct current (a fortieth) less

(b)(i)

after the generators

or before the transmission/power line(s any correct reference to location

1

to decrease the loss of energy/heat/power accept ‘less voltage loss in transmission’

or to decrease the current

1

(ii)

1 1

or to increase the efficiency or to increase distance of transmission Total 4 marks

Question 16 (a)(i)

(ii) (b)

all points plotted correctly (2)

four points plotted correctly (1) do not credit o blobs which are 2 mm or more o points which are more than 1 mm out in any direction

3

2 (hours)

may ecf from graph

1

1 000 000 (Bq)

1 x 106 / million

1 Total 5 marks TOTAL FOR PAPER: 100 MARKS

Paper 2H Question 1 Answer(s)

Extra information

Mark(s) 3

all four correct (3) or any two correct (2) or any one correct (1) do not credit lines connected to any box with two (or more) lines to/from

(a)

(b) all four correct (3) or any two correct (2) or any one correct (1) do not credit lines connected to any box with two (or more) lines to/from

3


brass

accept ‘metal’ or any reasonable choice of a named metal e.g iron or steel but not for example ‘gold’, sodium’, ‘platinum’,etc

1

(b)(i) (ii)

green and yellow (the metal case of) the iron

both but in either order appliance / metal

1 1

(c)

to prevent the user getting a shock/ electrocution

to carry current to the earth / the groun there is a fault / loose connection / wire (in the iron) or so current does not go through pers

1

(d)

use of insulated/ plastic casing/cover/correct place dop No need for earth (wire) / use 2-wire electrical parts can not be touched less/no chance of shock

1 1 1 Total 7 marks

Question 3 Answer(s) (a)(i)

Extra information

Mark(s)

centre of X along the vertical line

1

within logo, +/- 1 mm horizontally (ii)

B A C

All correct (2) Any correct (1)

2

(iii)

Air resistance

Drag or air friction

1

Slope/gradient (of the line) 500 (m) (2)

Line increasing / line going up or any clear indication, on the graph or elsewhere, that the distance is represented by (some of) the area under the graph (1) e.g. ½ (20 × 30) = 300 incorrect use of s = ut + ½ at2 scores 1

1 2

(b)(i) (ii)

Total 7 marks Question 4 (a)(i) (ii) (iii)

Reflected 3.5 (s) 1155 (m) ecf

(b)

Frequency (of the echo)

Do not accept ‘bounced’ or echoed’ or 330 x 3.5 (1) may ecf from (a)(ii) or sfs Or loudness / volume / amplitude Not sound of the echo Allow ‘shorter delay’ (2)

1 1 2 2


conduction and convection

(b)

silver(ed surface)

(c)

both either order

1 2

reflects (radiant) (heat) / infra red radiation (back into flask) / contents dop

or is a poor emitter or absorber (of radiation/infra red)

(metal) better (heat) conductor

or poorer (heat) insulator

(so contents) will cool more quickly / lose heat

or not keep warm for long do not credit just ‘will not keep warm’

casing becomes hot

accept argument based on cold contents

max 2

Total 5 marks


Extra information

(a)

0.025 (m2)

Or 0.25 x 0.1 (1) 10 x 25 (1)

2

(b)(i)

pressure = force ÷ area

Or p = F ÷ A Or any transposed version

1

4800 (Pa) (2)

or 4.8 kPa (2) or 120 ÷ 0.025 (1) may ecf from (a) or sfs

2

(ii)

Mark(s)


Direct current (a fortieth) less

(b)(i)

after the generators

or before the transmission/power line(s any correct reference to location

1

to decrease the loss of energy/heat/power accept ‘less voltage loss in transmission’

or to decrease the current

1

(ii)

1 1

or to increase the efficiency or to increase distance of transmission Total 4 marks

Question 8 (a)(i)

(ii) (b)

all points plotted correctly (2)

four points plotted correctly (1) do not credit o blobs which are 2 mm or more o points which are more than 1 mm out in any direction

3

2 (hours)

may ecf from graph

1

1 000 000 (Bq)

1 x 106 / million

1 Total 5 marks

Question 9 (a)(i)

(b)

(c)

use of F = ma a = 1440/60 = 24 m/s2 arrow : left to right

ignore minus sign N/kg

1 1 1 1

in correct place

judged horizontal or parallel to seat belt seen anywhere arrow or its extension goes through region marked as ‘seat belt’ dop

vector

not ‘physical’

1

1

Total 6 marks Question 10

(a)(i) (ii)

Answer(s)

Extra information

Mark(s)

arrow from negative to positive electrons are negatively charged they flow from negative to positive

does not have to be on plate

1

allow correctly placed e¯ on diagram so are attracted to positive/ repelled by negative no ecf

1 1

(b)

the volt is a joule per coulomb

joule = coulomb x volt

1

(c)

larger resistance/doesn’t conduct/ no free electrons

no electrons move or flow (2)

1

ignore ‘heat’

1 1

less/no current less/no power/energy (transferred)


R

1

total internal reflection (takes place at the surface) dop

1

(b)(i) (ii)

sin c = 1/n wherever seen 49º No UP

1/sin c = n 48.8º / 48.7º / 48.75º no ecf

1 1

(c)(i)

continues out of tank bends downwards dop

ignore reflections

1 1

hits surface at an angle less than critical angle/ angle Q

goes from more dense to less dense / gets faster

1

therefore refraction takes place/ enters air at angle P

refracts/bends away from normal

1

(ii)

No ecf


formula / ½ × 0.400 × 25 =5 J

(b)

Formula / 0.40 x 10 x 0.75 = 3 (J)

(c)(i)

5–3=2 J

1 1 1 ignore unit ecf from (a) and (b) using appropriate working if shown not dop

1 1 1 1

Answer(s) (c)(ii)

Extra information

Mark(s)

Conservation of energy

1

means work = ke – pe

ke = wd + pe 1 accept ‘this is the minimum work done if the technician just lets the hammer fall (onto the nail) for both marks Total 9 marks

frequency amplitude / maximum displacement

period or rate not ‘size’

Question 13 (a)(i) (ii)

1 1

(b)

(c)(i) (ii)

1 1 1

smaller amplitude same frequency Independent of (c)(i) further away from source/ quieter frequency/ pitch/ wavelength unchanged (by reflection)

1 1 1 energy lost to board/ smaller amplitude 1 can score 2 marks for a full explanation of one point e.g. ‘quieter because not 100% reflection’ or ‘same pitch because the source is not moving’ Total 9 marks

Question 14 (a)(i) (ii) (b)(i) (ii) (iii)

120 x 0.025 = 140 x V V = 0.0214

1 1

0.021

fixed mass no temperature change

amount/ number of molecules

1 1

mass / volume increased same mass/amount decreased volume

only awarded here No ecf from (a)(i) Must ecf from (b)(ii)

1 1 1 1 Total 8 marks


Extra information

(a)(i) (ii) (iii)

I downwards M from N to S F out of the paper

seen anywhere in circuit

(b)

increase the current

reduce resistance / increase power supply / thicker wire / shorter (connecting) wire

can be scored if I and/or M missing must be consistent with I and M if both shown

Mark(s ) 1 1 1

1

move poles closer together

1 stronger field/ magnets

(c)

liquid (at room temperature) metallic conductor to allow the end of the wire to move non-magnetic

ANY TWO

1 1


-4 +1

0

0

0

(b)

3 2

(c)

protons (and electrons) neutrons

1 accept 1 instead of +1

1 1 1 1 1 1

‘atomic number’ nucleons/ nucleon number/ mass number

1 1 Total 9 marks

Question 17 (a)

A : (most of) the atom is empty / space / hollow

OWTTE : e.g.’nucleus is a long way from electrons’ not homogeneous

1

(b)

B: small(er than atom) massive

larger than alpha particle heavy / very dense

1 1

(c)

C : same as alpha / + ve like charges repel

dop

1 1 Total 5 marks

Question 18

(a)

Answer(s)

Extra information

neutron uranium kinetic products

plutonium do not allow ‘heat’ fragments / neutrons

Mark(s) 1 1 1 1

(b) H Ba J Kr K n L n M n

1 out of 2 if wrong way round

1 1 1

Total 7 marks TOTAL FOR PAPER: 120 MARKS

Paper 3 Question 1 Answer(s)

Extra information

Mark(s)

76 (mm) (clamp) stand

allow 75.5 to 76.4 accept ‘retort stand’

1 1

hang the weight/plumb line next to the tube (1) check same distance top and bottom (1)

‘tie on’ = 0/2

2

(c)

stopwatch/ stopclock/ light gates/ electronic/electric timer/ multiflash camera

do not credit clock/chronometer do not credit just ‘timer’

(d)

ruler/ metre rule/ measuring tape

(e)

magnet next to (steel) ball / (bottom of) tube/bung (1) lift/ drag the ball out of the tube (with the magnet) (1)

(f)

any two 1 mark each * not all readings same/ there will b variations * to give an average this increases accuracy/ reliability * (this tends) to cancel out inaccuracies/ errors * allows anomalous result(s to be or words to that effect identified (and discounted)

2

(g)(i)

faster/ more quickly/ with a greater speed/velocity (electronic) thermometer/ temperature probe

1

(a) (b)(i) (ii)

(ii)

or (they) are/ appear to be parallel

(1) 1

1 Do not credit either mark for magnet in the tube of oil. Do not credit 2nd mark for magnet at the the tube to attract the steel ball

2

1 Total 12 marks

Question 2 (a) (b)

i = 32-34 (1) ray box/ light box

r = 60 (1)

(c)(i)

appropriate headings (1) all in order (1) unit given as degrees / o seen anywhere at least once (1) not 0C

or laser/ torch with slit or suitable diagram example i measured in 0 r measured in 0 10 15 15 23 20 32 25 42 30 53 35 65

2 1 3

(c)(ii)

Answer(s)

Extra information

both axes labelled (1) i on X axis r on Y axis (1) all points correctly plotted (3) i.e. to within 1 mm in any direction

no need to include degrees/ ˚

smooth curve /curved line (1)

Mark(s) 6

deduct 1 for up to each of three points is incorrect or a blob i.e. 2mm or more diameter either for the plotted points or for the plotted points and the origin do not credit dot to dot and/or straight with or without a ruler do not credit lines more than 1 mm thick

(c)(iii)

correct reading from candidate’s graph when curve/line extrapolated to r = 90 o curve-extrapolation must be shown line-extrapolation need not be shown

1

Total 13 marks Question 3 (a)(i)

(ii)

(b)(i) (ii) (c)(i)

measure (the length of) each/ one side (1) volume = l x b x h or v = l 3

(1)

water in measuring cylinder difference in readings (= volume of pebble)

(1) (1)

(top pan) balance 78 either 2.4 in the table

(3)

if measurements have been taken from the diagram, look for correct idea(s) or words to that effect

2

2 or correct description of the use of eureka can/ overflow can accept electric/electronic/digital balance Or 0078

1

or 98 ÷ 41 = 2.39……

(1) (1)

3

1

(ii)

mass and volume are (only) to 2 significant figures (1) (so) result cannot be more precise (than this) (1)

allow ‘all the other densities are to 2 significant figures’ for 1 mark

2

(iii)

(that) three of the objects are made of the same (sort of) glass (1) (that) the other two are made of a different sort (1)

or correct from candidate’s table or words to that effect or correct from candidate’s table or words to that effect

2

(c)(iv)

No; only three made of the same (sort of) glass (1)

or correct from candidate’s table 1 or words to that effect Total 14 marks


Extra information

(a)(i) (ii)

5.2 6.6

(b)

suitable suggestion

(1)

appropriate explanation

(1)

(c)(i)

Mark(s) 1 1

Examples: to stop light getting in through the side(s) (1) as you only want light to get in through the (open) end (1) to reduce/stop reflection(s) (from the inside surface of the tube) (1) as you only want to measure the light which comes directly into the tube (1)

or suitable comment re the ‘tube’ or suitable comment re ‘black’

do not credit just ‘focuses the light’

resistance (1) direction/angle … degrees (1)

both required

(ii)

276-280 (1) ……96-100

(iii)

(iv)

(1)

2

2 accept any answer in these ranges 1 mark only if both correct but order reversed

2

500 (Ω)

or correct reading from clear extrapolation on the graph unit not essential

1

360° is the same (direction) as 0° (1) (so) the tube is back where it started (1)

or words to that effect 2 these marks should only be credited if 500 has been given in (c)(iii) Total 11 marks TOTAL FOR PAPER: 50 MARKS

Examiners’ Report IGCSE Physics (4420)

June 2006 delivered locally, recognised globally

Examiners’ Report

June 2006 All the material in this publication is copyright © Edexcel Limited 2006

PHYSICS 4420, CHIEF EXAMINERS’ REPORT Paper 1F General Comments Questions 1 to 8 only appear on this paper and were targeted at candidates likely to achieve grade F. Questions 9 to 16 were targeted at grade C candidates and are common with the Higher Tier paper. The great majority of the candidates taking this paper had been entered for the most appropriate tier. Question 1 In part (a) most realised that the magnets would attract. However a small minority lost their first mark because they ignored, or overlooked, the instruction to ‘Add an arrow to each magnet…’. In (b) most selected the drawing pin and the needle and nearly all of these made the same choice in (ii). Most followed the instructions in (c). Some used the dotted box to show the pattern of the magnetic field around a bar magnet, but they generally obtained all three marks. Question 2 This question was well answered with only the occasional candidate giving half dimensions in (i) or arriving at an answer of 0.2 Hz or 80 Hz in (b)(ii). Question 3 It seemed that many candidates should have given themselves time to think before answering this question. For example, many did not seem to realise that the wall heater must be on the wall near to the temperature of 50 ˚C in Room A. Question 4 This question was better answered than a question on the same section of the specification in 2005. However, only a minority gained full marks. Question 5 In (a) few realised that the diagram shows that energy is conserved. However, other parts were much better answered with nearly all gaining the mark in (b). Question 6 This question was generally well answered but in (d) some gave a unit of energy rather than a unit of power. Question 7 Most selected perspex and polythene in (a) but in (b) only a minority knew that rubbing with a cloth is an example of charging by friction. In (c) some wrongly suggested that positive charge is able to move. In (d)(i) many knew that the danger was that a spark could trigger an explosion, but in (d)(ii) fewer knew that either the tank and nozzle should be connected by means of an electrical conductor or that both should be earthed. Question 8 This was generally well answered with most candidates showing, in their ‘gas’ diagram, four or more particles moving at random and more spaced out than in the ‘liquid’ diagram. However in their ‘solid’ diagram, although nearly all showed the

particles closer than in the liquid, a minority failed to indicate that the particles are vibrating. Question 9 Part (a), on the uses of electromagnetic radiation, proved slightly easier than (b), about the harm caused, but both were generally well answered. Question 10 In (b)(i) only a minority knew that the other end of the earth wire from the plug is connected to the metal frame/case of the appliance. In (d) there were some imaginative suggestions about what double insulation might be because it was confused with double glazing or some feature of heat transfer. Question 11 Surprisingly few realised that arrow C points downwards from the centre of gravity even though almost all candidates identified force C as ‘weight’. In (a)(iii) air resistance (or drag) was the answer expected but many restricted themselves to just ‘friction’. In (b), some who knew the feature was the gradient spoiled their answers by describing it as an ‘increasing gradient’. In (b)(ii) some secured one mark for ‘area under the graph’ but were not able to calculate this. Question 12 Generally well answered. In (b), increasing frequency of the echo as the ship neared the cliff was a more popular answer than the increasing volume of the echo. Question 13 A generally good response, though in (c) few seemed to realise that all vacuum flasks lose heat from their hot contents but that metal flasks are likely to do so more quickly. Question 14 Most candidates identified the dimensions of the base of the block but only a small minority converted from centimetres to metres. Question 15 This question was generally well answered. However, many were not able to locate a stepup transformer in the system to transmit electrical energy from power stations and only a minority could state why the voltage is increased. Some tried to explain how it is increased in a transformer, which is not the question that was asked. Question 16 A well answered question, but some did not seem to understand that if a megabecquerel really does equal 1000 becquerels it would be a kilobecquerel. A minority produced uncertain decay curves. Their efforts would be improved if they used the technique of rotating the page to put the wrist on the inside of the curve.

Paper 2H General Comments Questions 1 to 8 were common to this paper and the Foundation Tier paper. Much of the content of questions 9 to18 was from the ‘Higher Tier only’ parts of the specification. Some work of a very high standard was seen, with the vast majority of candidates entered for the correct tier. Question 1 In part (a) candidates were asked to link named electromagnetic radiations to the uses of these radiations. The use of gamma rays and ultraviolet was well known although a few candidates mixed up the uses of infra-red and microwaves. In part (b), boxes with the above named radiations had to be linked to the harm that they could cause. A common error was to link ultraviolet to skin burns and infra-red to blindness instead of the other way round. The entire question was drawn from the phrases used in the specification. Question 2 A drawing of a three-pin plug was shown. Candidates were asked what the pins were made of, the colour of the insulation of the earth wire, what this wire was connected to and its purpose. It is appreciated that these plugs are not in use worldwide but an attempt has been made in the recommended books to show clearly the structure of these plugs. Apart from a few candidates who were unclear about the colours used, these parts were well answered. Part (d) showed that many candidates were unclear about the use of double insulation. Two marks were awarded for stating that the cover of the appliance is made from an insulator but many candidates thought that the connecting wires had an extra layer of insulation since the term ‘insulation’ had been used in (b)(i). A small number of candidates misinterpreted the symbol and described cavity wall insulation. Question 3 Part (a)(i) required candidates to mark with an X the centre of gravity of a racing car whose diagram showed an unlabelled vertical arrow pointing downwards to represent its weight. A significant number of candidates did not answer the question. Of those who did, many marked the X too far from the vertical line in question. Part (a)(ii) asked candidates to complete a table linking named forces acting on the car to letters on the diagrams. Errors were very rare. Part (b)(i) showed a velocity-time graph for a racing car accelerating from an initial velocity of 10 m/s. Asked what feature of the graph showed acceleration, candidates were expected to comment on the slope of the line. Instead many simply wrote that it speeds or that it accelerates. Some answers just mentioned a straight line without any reference to slope. Part (b)(ii) required a calculation of the distance moved. Few candidates got the right answer because although they correctly calculated the area of a triangle (300 m) they forgot to add the area of the rectangle (200 m) due to the car not starting from rest. Question 4 A drawing showed a stationary ship and a distant cliff. In (a)(i) practically all candidates knew that the echo from the cliff of the sound from the ship’s foghorn was due to reflection.

In (a)(ii) most candidates knew that the time taken for the sound to travel back from the cliff to the ship was half the value of the time lapse between the foghorn sounding and its echo being heard back on the ship. In (a)(iii) calculations of the distance of the ship from the cliff given the speed of sound were almost always correct. A small number of candidates mistakenly used a speed of 300 m/s rather than the given value of 330 m/s. This type of error is thankfully rare but is penalised. In part (d) candidates were asked how the captain could tell that the moving ship was getting closer to the cliff when the foghorn was sounded every ten seconds. Many good answers were seen, referring to the increased loudness, the increased frequency or the shorter time delay. Answers stating that the sound travelled back faster were less satisfactory. Question 5 In (a) practically all candidates knew that heat cannot be transferred through a vacuum by conduction or convection. In (b) most knew that the feature shown in a diagram of a vacuum flask that reduced energy transfer by radiation was the double-walled container made of silvered glass. In (c) candidates were asked to explain one disadvantage, apart from weight, of a vacuum flask in which the case and double-walled container were both made from metal. Some very good answers were seen but a few candidates still referred to the weight and the possibility of it breaking when dropped on the floor due to its weight, even though the stem of the question stated that such flasks were both heavier and stronger than plastic ones. Question 6 A diagram showed a rectangular block, giving its dimensions. In (a) candidates had to calculate the area under the block. The dimensions were given in cm and the answer was expected in m2. An error at this stage was carried through and lost a maximum of one mark. In (b) candidates were asked to state the equation which relates area, force and pressure and a number of mistakes were seen. If candidates had been asked a similar question relating pressure, force and area many more would have been successful, giving p = F/A (in words). However, because convention dictates that the quantities must be given in alphabetical order a number of candidates tried but failed to get an unfamiliar expression with A as the subject (A = F/p). Candidates need to know that they should present the more familiar expression in situations like this. Question 7 In (a) practically all candidates knew what the letters d.c. stood for and that fewer coils are needed on the output coil than the input coil of a step-down transformer. In (b)(i) candidates were asked where step-up transformers were used in the system to transmit electrical energy. Some vague answers such as ‘at the power station’ were credited. In (b)(ii) many candidates knew that the voltage was increased to reduce current or energy loss or increase efficiency but some answers went on to refer to a reduction in resistance. A small number of candidates wrote that a voltage increase leads to a larger current. Question 8 In (a)(i) the data from a table showing activity against time for a radioactive isotope was plotted and a curve of best fit drawn. Very few errors such as misplotting were seen. A small number of candidates joined neighbouring points with a ruler. For the determination of half life in (a)(ii) practically all candidates used the data from the table rather than taking values from the graph. This gave the correct, exact

answer of 2 hours. Some successfully used the graph but a few candidates, having successfully plotted the point (0, 64 000), incorrectly halved 64 000 to draw a horizontal line from 34 000 instead of 32 000, even though again they had just successfully plotted the point (2, 32 000). In (b) most candidates did not know that 1 MBq is equal to 1 000 Bq, more often thinking it was 1 000 Bq. Question 9 In (a) candidates were asked to calculate the deceleration of a car passenger wearing a seat belt. Given the values of force and mass, practically all candidates were able to do this successfully and give its unit. In (b) candidates were asked to draw on the diagram of the passenger an arrow showing the direction and line of action of the given force. In (c) most candidates were able to gain full marks by stating that force is an example of vector quantity. Question 10 In (a)(i) many candidates were unable to show the correct direction of flow of electrons in a circuit consisting of a battery with its positive terminal labelled, an ammeter and metal plate. Hence they were unable to give an explanation of their answer for a further two marks. In (b) candidates were told that voltage is energy transferred per unit charge passed and asked to state the relationship between the volt, the joule and the coulomb. Answers were expected in terms of units but many featured a mixture of quantities and units, in particular voltage instead of volt. In (c) it was hoped that the previous parts would lead candidates to an answer including energy when asked to explain why a glass plate of the same size replacing the metal plate does not get warm. Many candidates scored two marks for noting that this insulator does not allow a current in it, but hardly any went on to state that as a result little or no energy was transferred to the glass slide. Question 11 In (a)(i) many realised that only one of the angles shown could be greater than the critical angle but in part (ii) did not include the term ‘total internal reflection’ in their explanation. In part (b)(i) the request to state the relationship between critical angle and refractive index produced the same uncertain response seen in a previous examination series. The following was seen disconcertingly often: c = 1 / sin n. Part (c) required the drawing and explanation of a ray with an angle of incidence less than the critical angle leaving a tank of water and emerging into air. This was very well answered. Question 12 In (a) the calculation of kinetic energy (5J) given the mass and speed of a hammer hitting a nail was competently done and the appropriate unit given. In (b) the gravitational potential energy (3J) of the stationary hammer at a given height was also very well done, especially as a value for g was not provided. In (c) candidates were expected to account for the difference in their calculated values as the work done by the person using the hammer. Instead of determining this by 5J – 3J = 2J, many candidates repeated the previous calculation to determine the work done using ‘force × distance’ and so were unable to gain a further two marks for an explanation based on the conservation of energy.

Question 13 In (a) candidates showed a good understanding of the idea that the pitch of a sound depends on frequency and that the loudness depends on amplitude. In (b) candidates had to match sinusoidal wave patterns to descriptions relating to the volume and pitch of the sound. This was exceptionally well done with very few candidates failing to score three marks. In (c) candidates were shown the wave pattern received by a microphone close to a source of sound and asked to draw, on a grid alongside, the pattern for the sound received by a second microphone after the sound had reflected off a wooden board. An explanation was required. Many accurate, well drawn responses were seen with many candidates scoring all nine marks for this question. A few had explanations that contradicted their drawings. For example, an erroneously drawn wave with the same amplitude as the first one was referred to as being quieter and even having a smaller amplitude. Question 14 In (a)(i) a calculation using Boyle’s law was uncharacteristically badly answered with a substantial number of candidates trying to use the relationship p/V = constant. Furthermore, when an initial pressure of 120 kPa was increased by 20 kPa, the second pressure was often taken as 20 kPa instead of 140 kPa. Many candidates were unable to state two assumptions made in the calculations. In (b)(i) the definition of density occasionally referred to weight and area instead of mass and volume. The explanation as to why the density of air in a balloon increases when taken to the bottom of a swimming pool allowed for follow through marks from previous errors, but many candidates did not mention that mass remains unchanged. Question 15 In (a) candidates were shown a diagram of a flexible current-carrying copper wire dipping into a tray of mercury placed between the unlike poles of two bar magnets. They were then expected to use the Left Hand Rule to draw labelled arrows to show the directions of current, magnetic field and motion. A sizeable minority of candidates was unable to show the correct direction of the current given the positive and negative terminals of the power supply, and many showed two conflicting directions for the magnetic field. The direction of motion was often shown opposing the given direction of the current. In (b) and (c) candidates were asked to state two changes that could be made to increase the force acting on the wire and give two reasons why mercury was suitable for this demonstration. These parts were very well answered. Question 16 Candidates were asked to fill in gaps to show their knowledge of atomic physics and radioactivity. Many candidates scored all nine marks. In (a) candidates were asked to pick from numbers between –4 and +4 to show the changes in atomic number and mass number during alpha, beta and gamma decay respectively. A small number of candidates gave 4 instead of –4 for the change in mass number during alpha decay. In (b) the method of completing a nuclear equation by writing in the missing numbers, and in (c) the meaning of the term ‘isotope’, were both well known. Question 17 Candidates were shown the paths of three alpha particles passing through a gold atom. One went through undeviated, one was slightly deviated and the third one came back in the original direction. They were then asked to comment on the information provided by these paths on (a) the structure of the atom, (b) the size and mass of the nucleus and (c) the likely charge on the nucleus.

In (a) many candidates stated that the atom had gaps in it without specifying the nature of these gaps. In (b) the response ‘small’ and ‘massive’ or ‘heavy’ would have scored two marks. A response of ‘large’ or ‘big’ was only acceptable if this was in comparison with the alpha particle. Some unexpected confusion in (c) was seen, with responses such as ‘negative because the alpha is positive’. There was also a tendency to refer to ‘deflection’ instead of ‘repulsion’. A small minority of candidates stated the properties of the alpha particle or the path(s) throughout. Question 18 In (a) candidates were asked to complete sentences describing the process of nuclear fission. Few knew that the energy released is in the form of the kinetic energy of the fission products, referring instead to heat energy. In (b) the relative sizes of the incoming neutron, the fissioned nucleus, the fission fragments and the extra neutrons were expected to be linked with the symbols for U235, Ba-141, Kr-92 and the neutrons. Judging by the amount of crossing out, this produced some uncertainty. It seemed that many candidates could not bring themselves to fill in as many as three of the boxes with the symbol for the neutron.

Paper 3 Question 1 (a) Most candidates were able to measure the depth and write down an answer in the range 75.5 to 76.0 mm. (b) In (i) most candidates recognised that X was a stand and in (ii) many were able to describe how to check that the glass tube is vertical. Responses which involved tying the string of the plumb line round the top of the glass tube or lowering the plumb line into the tube full of oil were not credited. (c) Generally appropriately answered. (d) Generally appropriately answered. (e) Most candidates suggested putting the magnet next to the steel ball and carefully moving it upwards to drag the steel ball out of the oil. Responses which involved tying string to the magnet and dropping it into the oil did not get either mark; those who thought the magnet would be sufficiently powerful to lift the steel ball through the oil if placed at the open end of the tube only got one mark. (f) Most were able to explain why the experiment should be repeated several times. (g) This part was well answered by almost all candidates. Question 2 (a) Almost all candidates were able to use a protractor with sufficient accuracy. For angle i a measurement in the range 32˚ to 34˚ was required but for angle r, which is easier to measure on the diagram, the only accepted measurement was 60˚. (b) A wide range of acceptable responses was offered, from a covered torch with a slit to a laser. (c) Most candidates constructed a suitable table and inserted the readings in order. Points were in general accurately plotted and most recognised a curved line of best fit was more appropriate than a straight line. Some ‘curves’ did not gain credit because they were a series of lines drawn point to point, either with or without the assistance of a ruler. (d) A significant minority of candidates failed to extrapolate their curves to make a prediction in (iii).

Question 3 (a) Almost everyone correctly stated that the method is to measure the length of each side and to use the equation V = l x b x h, or, because it is a cube, to measure one side and to use the equation V = l3. In (ii) most had the right idea of partially filling the measuring cylinder with water, reading the volume, carefully adding the pebble, reading the new volume and then calculating the difference in the readings. Some correctly used a eureka can and a measuring cylinder. However, a small minority unsuccessfully proposed filling their measuring cylinder with water, adding the pebble and somehow measuring the overflow. (b) Most named the instrument correctly. However, it is not a ‘beam balance’ or a ‘weighing machine’. Nearly all candidates gave the correct answer in part (ii). (c) In part (i) nearly all gave the value as 2.4, and in part (ii) reasoned that this was appropriate because all the other densities have been calculated to two significant figures. This is correct and sensible and was worth one mark. However for two marks candidates needed to make the point that, as the mass and volume have only been measured to two significant figures, it is not possible sensibly to give the answer to more than two significant figures. One excellent answer stated that ‘The measurements for mass and volume are used to calculate the density and they are both to two significant figures. The density should also be to this degree of precision. To quote it to more significant figures would be implying it is more accurate than it really is’. In parts (iii) and (iv) nearly all candidates were able to write a suitable conclusion and to explain why the student’s prediction was incorrect. The small minority who lost marks in (iii) did so because they attempted to describe false relationships between mass or volume and density, eg ‘as mass increases so does density’. Question 4 (a) Both readings were almost always correct. (b) In general candidates made a variety of appropriate points and a typical two mark response was ‘The candidate uses a black tube to stop reflected light coming in from the sides. You only want to measure the light which comes straight into the tube from the measured direction’. (c) Both labels were usually completed correctly in part (i). In part (ii) a fairly high degree of accuracy was expected with answers in the ranges 276 to 280 degrees and 96 to100 degrees. Candidates who misunderstood the implication of the information at the start of the question, and who had accurate answers but in the reverse order, were awarded one of the two available marks. (d) Candidates either made a prediction of 500 Ω by reasoning that 360˚ is equivalent to 0˚, then explaining this in part (iv) and gaining all three marks, or extrapolated their curve and read where it crossed the 360˚ vertical for just one mark.

PHYSICS 4420 COURSEWORK, PRINCIPAL MODERATOR’S REPORT The number of students entered for this component of the IGCSE examination was as follows: Spec Code

Subject

Number entered in 2006

4420

Physics

97

Number entered in 2005 1

All the centres which entered students for this component of the examination had their science coursework moderated by Edexcel’s Co-ordinating Principal Moderator. The moderating instrument used was the Sc1 criteria as used by home centres, using exemplars provided by the JCQ (Joint Council for Qualifications) as a guide. Centres entering students for the coursework component of the IGCSE examinations in 2006 therefore had their coursework moderated to the same standards as for all home centres. Physics 4420 A range of tasks was seen this year. The most common was resistance in wires (or filament bulbs). This is the most common Physics task seen in UK centres, and it can achieve the full range of marks. One other appropriate task seen was ‘stretching springs in parallel’ . One centre presented tasks which were not investigations. These were ‘To study the reflection of light at a plane mirror’ and ‘To study the Principle of Moments’. Neither of these are true investigations because they merely require the student to prove an accepted scientific law. Such tasks do not allow the students to make a valid prediction since they are not undertaking true investigations. Centres are reminded that to fully achieve P8b, students need to clearly show how the preliminary work has affected their planning for the main task. It is not necessary to carry out the entire task as a trial run – only two values of the range chosen (normally the extremes of the range) are required, in order to see if the range chosen is appropriate. When awarding A6b, teachers need to bear in mind that the specification requirements are that the students should explain the science behind the results they have obtained. Merely describing the shape of the graph does not result in the student achieving A6b. For E4b, students are required to suggest at least one meaningful improvement to the technique used – and give some indication as to why the improvement(s) proposed would result in the obtaining of more accurate data.

PHYSICS 4420, GRADE BOUNDARIES

Grade

A*

A

B

C

D

E

F

G

Option 1

60

48

36

25

14

Option 2

61

49

37

26

15

Option 3

84

72

60

48

37

31

Option 4

85

73

61

49

38

32

Option Option Option Option

1: 2: 3: 4:

Papers Papers Papers Papers

03 04 03 04

/ / / /

1F 1F 2H 2H

Note: Grade boundaries may vary from year to year and from subject to subject, depending on the demands of the question paper.