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Cambridge International AS & A Level

PHYSICS 9702/21
Paper 2 AS Level Structured Questions October/November 2021
MARK SCHEME
Maximum Mark: 60

Published

This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the
examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the
details of the discussions that took place at an Examiners’ meeting before marking began, which would have
considered the acceptability of alternative answers.

Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for
Teachers.

Cambridge International will not enter into discussions about these mark schemes.

Cambridge International is publishing the mark schemes for the October/November 2021 series for most
Cambridge IGCSE™, Cambridge International A and AS Level components and some Cambridge O Level
components.

This document consists of 12 printed pages.

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Generic Marking Principles

These general marking principles must be applied by all examiners when marking candidate answers. They should be applied alongside the
specific content of the mark scheme or generic level descriptors for a question. Each question paper and mark scheme will also comply with these
marking principles.

GENERIC MARKING PRINCIPLE 1:

Marks must be awarded in line with:

• the specific content of the mark scheme or the generic level descriptors for the question
• the specific skills defined in the mark scheme or in the generic level descriptors for the question
• the standard of response required by a candidate as exemplified by the standardisation scripts.

GENERIC MARKING PRINCIPLE 2:

Marks awarded are always whole marks (not half marks, or other fractions).

GENERIC MARKING PRINCIPLE 3:

Marks must be awarded positively:

• marks are awarded for correct/valid answers, as defined in the mark scheme. However, credit is given for valid answers which go beyond the
scope of the syllabus and mark scheme, referring to your Team Leader as appropriate
• marks are awarded when candidates clearly demonstrate what they know and can do
• marks are not deducted for errors
• marks are not deducted for omissions
• answers should only be judged on the quality of spelling, punctuation and grammar when these features are specifically assessed by the
question as indicated by the mark scheme. The meaning, however, should be unambiguous.

GENERIC MARKING PRINCIPLE 4:

Rules must be applied consistently, e.g. in situations where candidates have not followed instructions or in the application of generic level
descriptors.

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GENERIC MARKING PRINCIPLE 5:

Marks should be awarded using the full range of marks defined in the mark scheme for the question (however; the use of the full mark range may
be limited according to the quality of the candidate responses seen).

GENERIC MARKING PRINCIPLE 6:

Marks awarded are based solely on the requirements as defined in the mark scheme. Marks should not be awarded with grade thresholds or
grade descriptors in mind.

Science-Specific Marking Principles

1 Examiners should consider the context and scientific use of any keywords when awarding marks. Although keywords may be present, marks
should not be awarded if the keywords are used incorrectly.

2 The examiner should not choose between contradictory statements given in the same question part, and credit should not be awarded for
any correct statement that is contradicted within the same question part. Wrong science that is irrelevant to the question should be ignored.

3 Although spellings do not have to be correct, spellings of syllabus terms must allow for clear and unambiguous separation from other
syllabus terms with which they may be confused (e.g. ethane / ethene, glucagon / glycogen, refraction / reflection).

4 The error carried forward (ecf) principle should be applied, where appropriate. If an incorrect answer is subsequently used in a scientifically
correct way, the candidate should be awarded these subsequent marking points. Further guidance will be included in the mark scheme
where necessary and any exceptions to this general principle will be noted.

5 ‘List rule’ guidance

For questions that require n responses (e.g. State two reasons …):

• The response should be read as continuous prose, even when numbered answer spaces are provided.
• Any response marked ignore in the mark scheme should not count towards n.
• Incorrect responses should not be awarded credit but will still count towards n.
• Read the entire response to check for any responses that contradict those that would otherwise be credited. Credit should not be
awarded for any responses that are contradicted within the rest of the response. Where two responses contradict one another, this
should be treated as a single incorrect response.
• Non-contradictory responses after the first n responses may be ignored even if they include incorrect science.

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6 Calculation specific guidance

Correct answers to calculations should be given full credit even if there is no working or incorrect working, unless the question states ‘show
your working’.

For questions in which the number of significant figures required is not stated, credit should be awarded for correct answers when rounded
by the examiner to the number of significant figures given in the mark scheme. This may not apply to measured values.

For answers given in standard form (e.g. a × 10n) in which the convention of restricting the value of the coefficient (a) to a value between 1
and 10 is not followed, credit may still be awarded if the answer can be converted to the answer given in the mark scheme.

Unless a separate mark is given for a unit, a missing or incorrect unit will normally mean that the final calculation mark is not awarded.
Exceptions to this general principle will be noted in the mark scheme.

7 Guidance for chemical equations

Multiples / fractions of coefficients used in chemical equations are acceptable unless stated otherwise in the mark scheme.

State symbols given in an equation should be ignored unless asked for in the question or stated otherwise in the mark scheme.

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Abbreviations

/ Alternative and acceptable answers for the same marking point.

() Bracketed content indicates words which do not need to be explicitly seen to gain credit but which indicate the context for an answer.
The context does not need to be seen but if a context is given that is incorrect then the mark should not be awarded.

___ Underlined content must be present in answer to award the mark. This means either the exact word or another word that has the
same technical meaning.

Mark categories

B marks These are independent marks, which do not depend on other marks. For a B mark to be awarded, the point to which it refers must be
seen specifically in the candidate’s answer.

M marks These are method marks upon which A marks later depend. For an M mark to be awarded, the point to which it refers must be seen
specifically in the candidate’s answer. If a candidate is not awarded an M mark, then the later A mark cannot be awarded either.

C marks These are compensatory marks which can be awarded even if the points to which they refer are not written down by the candidate,
providing subsequent working gives evidence that they must have known them. For example, if an equation carries a C mark and the
candidate does not write down the actual equation but does correct working which shows the candidate knew the equation, then the
C mark is awarded.
If a correct answer is given to a numerical question, all of the preceding C marks are awarded automatically. It is only necessary to
consider each of the C marks in turn when the numerical answer is not correct.

A marks These are answer marks. They may depend on an M mark or allow a C mark to be awarded by implication.

Annotations

 Indicates the point at which a mark has been awarded.

X Indicates an incorrect answer or a point at which a decision is made not to award a mark.

XP Indicates a physically incorrect equation (‘incorrect physics’). No credit is given for substitution, or subsequent arithmetic, in a
physically incorrect equation.

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ECF Indicates ‘error carried forward’. Answers to later numerical questions can always be awarded up to full credit provided they are
consistent with earlier incorrect answers. Within a section of a numerical question, ECF can be given after AE, TE and POT errors,
but not after XP.

AE Indicates an arithmetic error. Do not allow the mark where the error occurs. Then follow through the working/calculation giving full
subsequent ECF if there are no further errors.

POT Indicates a power of ten error. Do not allow the mark where the error occurs. Then follow through the working/calculation giving full
subsequent ECF if there are no further errors.

TE Indicates incorrect transcription of the correct data from the question, a graph, data sheet or a previous answer. For example, the
value of 1.6 × 10–19 has been written down as 6.1 × 10–19 or 1.6 × 1019.
Do not allow the mark where the error occurs. Then follow through the working/calculation giving full subsequent ECF if there are no
further errors.

SF Indicates that the correct answer is seen in the working but the final answer is incorrect as it is expressed to too few significant
figures.

BOD Indicates that a mark is awarded where the candidate provides an answer that is not totally satisfactory, but the examiner feels that
sufficient work has been done (‘benefit of doubt’).

CON Indicates that a response is contradictory.

I Indicates parts of a response that have been seen but disregarded as irrelevant.

M0 Indicates where an A category mark has not been awarded due to the M category mark upon which it depends not having previously
been awarded.

^ Indicates where more is needed for a mark to be awarded (what is written is not wrong, but not enough). May also be used to
annotate a response space that has been left completely blank.

SEEN Indicates that a page has been seen.

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Question Answer Marks

1(a) mass / volume B1

1(b)(i) (vernier/digital) calipers B1

1(b)(ii) percentage uncertainty = (0.0004 / 0.0420) × 100 A1

= 1%

1(c)(i) kg m–3 = kg × mn / m or kg m–3 = kg × mn × m–1 M1

–3 = n – 1 and (so) n = –2 A1

1(c)(ii) (Δρ / ρ) = (ΔM / M) + 2(Δr / r) + (ΔL / L) C1

percentage uncertainty = [(0.001 / 1.072) + 2 × (0.0004 / 0.0420) + (0.0001 / 0.1242)] (× 100) C1

= 0.09% + 2 × 0.95% + 0.08% A1

= 2%

1(c)(iii) ρ = (1.072 × 0.0420–2) / (2.094 × 0.1242) C1

= 2337 (kg m–3)

∆ρ = 0.021 × 2337 C1

= 49 (kg m–3)

ρ = (2340 ± 50) kg m–3 A1

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Question Answer Marks

2(a) mass × velocity B1

2(b)(i) kinetic energy = ½mv2 C1

= ½ × 0.24 × 2.32 C1

= 0.63 J A1

2(b)(ii) change in momentum = ½ × 240 × 5.0 × 10–3 C1

= 0.60 N s A1

2(b)(iii) (change in velocity of Y) = 0.60 / 0.12 C1

( = 5.0 m s–1)

final velocity of Y = 5.0 – 2.3 A1

= 2.7 m s–1

or

(final momentum of Y) = 0.60 – 0.12 × 2.3 (C1)

( = 0.324 N s)

final velocity of Y = 0.324 / 0.12 (A1)

= 2.7 m s–1

2(c) sloping straight line from (0, 0) to t = 3.0 ms and another straight line continuous with the first from t = 3.0 ms to (5.0, 0) B1

lines showing maximum force of magnitude 240 N B1

lines wholly in the negative F region of the graph B1

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Question Answer Marks

3(a)(i) σ = F / xy B1

3(a)(ii) ε = (z – w) / w B1

3(a)(iii) E = σ/ε C1

= Fw / xy(z – w) A1

3(b)(i) extension = 2.2 mm (allow 2.0–2.4 mm) A1

3(b)(ii) strain energy = area under graph/line or ½Fx or ½kx2 C1

= ½ × 120 × 1.4 × 10–3 or ½ × 8.6 × 104 × (1.4 × 10–3)2 C1

= 0.084 J A1

3(b)(iii) (some of the) deformation of the wire is plastic/permanent/not elastic B1

or
wire goes past the elastic limit/enters plastic region

energy (that cannot be recovered) is dissipated as thermal energy/becomes internal energy B1

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Question Answer Marks

4(a) oscillations (of particles) are parallel to (the direction of) energy transfer B1

4(b)(i) (frequency varies as) vehicle moves relative to (stationary) observer C1

(vehicle) moving towards (observer) gives higher (observed) frequency (than 1.2 kHz) and (vehicle) moving away (from A1
observer) gives lower (observed) frequency (than 1.2 kHz)

4(b)(ii) Doppler effect B1

4(b)(iii) position of vehicle labelled ‘X’ at top (12 o’clock) position on track B1

4(b)(iv) position of vehicle labelled ‘Y’ at right-hand edge (3 o’clock) position on track B1

4(c) maximum frequency = 1.40 (kHz) or 1.40 × 103 (Hz) C1

1.40 = (1.2 × 320) / (320 – v) C1

v = 46 m s–1 A1

or

minimum frequency = 1.05 (kHz) or 1.05 × 103 (Hz) (C1)

1.05 = (1.2 × 320) / (320 + v) (C1)

v = 46 m s–1 (A1)

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Question Answer Marks

5(a) sum of current(s) in = sum of current(s) out M1

or
(algebraic) sum of current(s) is zero

at a junction (in a circuit) A1

5(b)(i) (current in R4 or R1 =) 0.30 + 0.30 B1

(= 0.60 A)

(R =) 2.4 / 0.60 = 4.0 (Ω) A1

or

(p.d. across R3 or R2 =) 2.4 / 2 (B1)

(= 1.2 V)

(R =) 1.2 / 0.30 = 4.0 (Ω) (A1)

5(b)(ii) E = 2.4 + 2.4 + 1.2 C1

= 6.0 V A1

or

total resistance = 10 (Ω) (C1)

E = 10 × 0.60 (A1)

= 6.0 V

5(c) total resistance increases B1

current decreases (in battery) so total power decreases B1

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Question Answer Marks

5(d) resistivity = RA / L C1

= 4.0 × π × (240 × 10–6)2 / 0.67 C1

= 1.1 × 10–6 Ω m A1

Question Answer Marks

6(a) α-particle mass given as 4u B1

α-particle charge given as (+)2e B1

both β-particles mass given as 0.0005 u B1

β+ charge given as (+)e and β– charge given as –e B1

(Completed table:
mass / u charge / e

α 4 (+)2

β+ 0.0005 (+)1

β– 0.0005 –1
)

6(b)(i) neutron decays into proton and an electron / β– particle B1

6(b)(ii) down to up B1

6(b)(iii) (electron) antineutrino(s) emitted B1

energy (released in decay)/momentum shared between antineutrino and β– particle B1

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