Physics OCR Mark Scheme, High school final essays of Physics

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Oxford Cambridge and RSA Examinations

GCE

Physics A

Unit H556/02: Exploring physics

Advanced GCE

Mark Scheme for June 2017

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This mark scheme is published as an aid to teachers and students, to indicate the requirements of the examination. It shows the basis on which marks were awarded by examiners. It does not indicate the details of the discussions which took place at an examiners’ meeting before marking commenced.

All examiners are instructed that alternative correct answers and unexpected approaches in candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated.

Mark schemes should be read in conjunction with the published question papers and the report on the examination.

OCR will not enter into any discussion or correspondence in connection with this mark scheme.

© OCR 2017

H556/02 Mark Scheme June 2017

Abbreviations, annotations and conventions used in the detailed Mark Scheme (to include abbreviations and subject-specific conventions).

Annotation Meaning / alternative and acceptable answers for the same marking point

reject Answers which are not worthy of credit

not Answers which are not worthy of credit

ignore

Statements which are irrelevant

allow Answers that can be accepted

( ) Words which are not essential to gain credit

___ Underlined words must be present in answer to score a mark

ECF Error carried forward

AW

Alternative wording

ORA Or reverse argument

H556/02 Mark Scheme June 2017

MARKING INSTRUCTIONS

Generic version as supplied by OCR Sciences

CATEGORISATION OF MARKS

The marking schemes categorise marks on the MACB scheme.

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

M marks: These are method marks upon which A -marks (accuracy marks) later depend. For an M -mark to be scored, the point to which it refers must be seen in the candidate’s answers. If a candidate fails to score a particular M -mark, then none of the dependent A -marks can be scored.

C marks: These are compensatory method marks which can be scored 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 it. 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 given.

A marks: These are accuracy or answer marks, which either depend on an M -mark, or allow a C -mark to be scored.

Note about significant figures:

If the data given in a question is to 2 sf, then allow to 2 or more significant figures. If an answer is given to fewer than 2 sf, then penalise once only in the entire paper. Any exception to this rule will be mentioned in the Additional Guidance.

H556/02 Mark Scheme June 2017

SECTION B

Question Answer Marks Guidance 16 (a) (When two or more waves meet at a point in space) the resultant (displacement) is equal to the (vector) sum of the individual displacements of waves (meeting at a point)

B1 (^) Allow total /  / net for resultant Not amplitude for displacement

(b) (i) Clear evidence of at least two fringe separations used to determine x and x in the range 7.0 to 9.0 mm

0. 25  10 ^3  8  10 ^3

 (Allow any subject)

 = 4.7  10 -^7 (m)

B

C

A

Expect 8 (mm)

Allow ecf for incorrect value of x

(ii) Red light has longer wavelength /  and separation

between fringes increases (AW)

Separation between fringes justified in terms of x  

or x =  D / a , D and a are constants

M

A1 Allow other acceptable labels for D and a

Total 6

H556/02 Mark Scheme June 2017

Question Answer Marks Guidance 17 (a) Any one from: current, temperature, light intensity and amount of substance / matter

B1 Not : ampere, kelvin, candela and mole Not correct quantity with its unit, e.g. current in A or current (A) (b) (i)

A

L

R

 and

2

d

A

2

d

L

R



X ^ and Y 2

d

L

R



Clear steps leading to 2

d

L

R

M

A

(ii)1 Ruler / tape measure (for L ) and micrometer (for d ) B1 Allow (vernier / digital) calipers or travelling microscope for micrometer (ii) R = 2.3(4) ()

or

  or 0.0327 or 3.27%

absolute uncertainty in R = 0.0327 2.34 = 0.

R = 2.3  0.1 ()

C

C

C

A

Allow other correct methods for getting 2.3  0.1 ()

Allow 2 or more sf for this C1 mark Note 0.0105 or 1.05% or 0.0222 or 2.22% scores this mark, allow 2sf or more

Allow : 2.34  0.08 () Note use of R X or R Y instead of R can score the second and third C1 marks only (ii)3 (The actual) R is large(r) because (the actual) d is small(er) or (the actual) A is small(er) or R  1/ d^2

B1 Allow : The calculated R is small(er) because (the measured) A is large(r) or R  1/ d^2 Total 9

H556/02 Mark Scheme June 2017

Question Answer Marks Guidance (b)*

Level 3 (5–6 marks) Clear description including a reasonable estimate of r and clear limitations There is a well-developed line of reasoning which is clear and logically structured. The information presented is relevant and substantiated.

Level 2 (3–4 marks) Some description with an attempt to estimate r and some limitations There is a line of reasoning presented with some structure. The information presented is in the most part relevant and supported by some evidence.

Level 1 (1–2 marks) Limited description There is an attempt at a logical structure with a line of reasoning. The information is in the most part relevant.

0 marks No response or no response worthy of credit.

B1  6

Use level of response annotations in RM Assessor, e.g. L2 for 4 marks, L2^ for 3 marks, etc. Indicative scientific points may include: Description and estimation  Correct circuit with (variable) resistor, ammeter and voltmeter  Correct symbols used for all the components  R changed to get different values for P  R = V / I (using ammeter and voltmeter readings) or R measured directly using an ohmmeter with the variable resistor isolated from the circuit or R read directly from a resistance box  Power calculated using P = V^2 / R or P = VI or P = I^2 R  The value of r is between 1.0 to 3.0   A smooth curve drawn on Fig. 18.2 (to determine r)  A better approximation from sketched graph or r is between 1.5 and 2.7   Any attempt at using E = V + Ir , with or without the power equation(s) to determine r - even if the value is incorrect

Limitations  ‘More data’ required  Data point necessary at R = 2.0  / More data (points) needed between 1 to 3   No evidence of averaging / Error bars necessary (for both P and R values) Total 11

H556/02 Mark Scheme June 2017

Question Answer Marks Guidance

19 (a) Photon(s) mentioned

One-to-one interaction between photons and electrons

Energy of photon is independent of intensity / intensity is to do with rate (of photons / photoelectric emission) / photon energy depends on frequency / energy of photon depends on wavelength / photon energy  frequency /

photon energy  1/ 

energy of uv photon(s) > work function (of zinc) / frequency of uv > threshold frequency

B

B

B

B

Allow ‘photon absorbed by an electron’ Allow : collide etc. for interaction

Allow E = hf or E = hc / 

Allow energy of light photon(s) < work function (of zinc) / frequency of light < threshold frequency Allow  instead of > here Not f > f 0 (b)

34 8





or 6.86  10 -^19 (J)

E = 5.1  1.60  10 -^19 or 8.16  10 -^19 (J)

max kinetic energy = (8.16 – 6.86)  10 -^19

max kinetic energy = 1. 3  10 -^19 (J)

C

C

A

Note : Using 5.1 and not 8.16  10 -^19 cannot score this mark or the next mark

Allow 2 marks for 0.81 eV

(c) Any three from: The electrons are repelled by C / electrons travel against the electric field (AW) The electrons are emitted with a ‘range’ of speed / velocity / kinetic energy (AW) As V increases the slow(er) electrons do not reach C and hence I decreases maximum KE in the range 2.1 eV to 2.2 eV or 3.36  10 -^19 J to 3.52  10 -^19 J

B1  3

Note ‘range’ can be implied by ‘highest’ or ‘lowest’

Allow ‘find p.d. when current is (just) zero, and then KE = e  V ’

Total 10

H556/02 Mark Scheme June 2017

Question Answer Marks Guidance

21 (a)  = 7.2  10 -^12  1.2  10 -^3 /4.0  10 -^4

permittivity = 2.2  10 -^11 (F m-^1 )

C

A

Allow any subject

Allow o instead of 

Note answer to 3 sf is 2.16  10 -^11 (F m-^1 ) Allow 1 mark for bald 2.4; relative permittivity calculated

(b) (i) (^) capacitance of two capacitors in series = 500 (F)

C = 1000 + 500

C = 1500 (F)

C

A

(ii) (^) V = 1.5  e-12/

V = 0.67 (V)

C

A

Possible ecf from (i)

Allow 1 mark for 0.83 V, V = 1.5[1 - e-12/15] used

Total 6

H556/02 Mark Scheme June 2017

Question Answer Marks Guidance

22 (a)*

Level 3 (5–6 marks) Clear evaluation of Fig. 22.1 and clear analysis There is a well-developed line of reasoning which is clear and logically structured. The information presented is relevant and substantiated.

Level 2 (3–4 marks) Some evaluation of Fig. 22.1 and some analysis There is a line of reasoning presented with some structure. The information presented is in the most part relevant and supported by some evidence.

Level 1 (1–2 marks) Limited evaluation of Fig. 22.1 or limited analysis There is an attempt at a logical structure with a line of reasoning. The information is in the most part relevant.

0 marks No response or no response worthy of credit.

B1  6

Use level of response annotations in RM Assessor, e.g. L2 for 4 marks, L2^ for 3 marks, etc.

Ignore incorrect references to the terms precision and accuracy

Indicative scientific points may include:

Evaluation of Fig. 22.  Comment on the line  The straight line misses one error bar / anomalous point ringed or indicated  Too few data points plotted  The triangle used to calculate the gradient is (too) small  Some plots should have been repeated / checked  No error bars for current  ‘Not regular intervals’ (for current)  No origin shown (AW)

Evaluation of analysis  The value of B is close to the accepted value  The difference of only 7%  No absolute or percentage uncertainty in B shown (AW)  Worst-fit line or maximum / minimum gradient line could have been used to determine the (absolute or percentage) uncertainty in B  F against I graph should be a straight line or  BL = gradient (any subject)

H156/02 Mark Scheme June 2017

Question Answer Marks Guidance 23 (a) Any two from: It acts between quarks / nucleons / hadrons ‘Short-range’ force Repulsive below (about) 0.5 fm Attractive up to (about) 3 fm

B1  2

Allow any correctly named particle

Allow any value between 0.5 fm and 5 fm

(b) (i) proton = u u d or neutron = u d d B

(ii) d  u  ^01 e

 (e)

M

A

Allow the equation expressed in words

Allow udd  uud  ^01 e

Allow ^01 

Not e-^ for electron

Allow this mark if electron written as e-^ or -

(c) (^) mass (of nucleus)  A

volume (of nucleus)  radius^3  A and clears steps using

 = m / V to show density is (about) the same

B

B

Allow mass = Am , mass = Au , etc.

Allow r or R for radius Allow any sensible constant in front of the r^3

Total 7

H156/02 Mark Scheme June 2017

Question Answer Marks Guidance

24 (a)^21 Hhas two nucleons

binding energy per nucleon = 1.1 MeV (per nucleon)

B

B1 Allow^ 1.76^ ^10 -^13 J (per nucleon)

(b) The protons / nuclei repel each other

(At high temperature) particles have more KE and hence can get close (enough to fuse)

B

B

Not atoms / particles

Allow ‘enough KE to get close’ Not atoms or ions

(c) E = hc / and E = mc^2 or E = 2  mc^2

31 8

34



maximum wavelength = 1.2  10 -^12 (m)

C

C

A

Allow hc / = 2 mc^2 with or without the factor of 2

Note : The mass must be 2 m e to score this and the next mark

Not de Broglie equation  = h / mv with speed of c ;

which gives 2.4  10 -^12 (m) Allow 2 marks for 6.6  10 -^16 (m); mass of neutron or proton used instead

Allow the following marks for 1.02 MeV recalled: E = 1.63  10 -^13 (J) C

13

34 8





 C

maximum wavelength =1.2  10 -^12 (m) A Total 7

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