A-level PHYSICS 7408/3A Paper 3 Section A Mark scheme June 2024

A-level PHYSICS 7408/3A Paper 3 Section A Mark scheme June 2024 MARK SCHEME –PHYSICS – 7408/3A – JUNE 2024 Mark schemes are prepared by the Lead Assessment Writer and considered, together with the relevant questions, by a panel of subject teachers. This mark scheme includes any amendments made at the standardization events which all associates participate in and is the scheme which was used by them in this examination. The standardization process ensures that the mark scheme covers the students’ responses to questions and that every associate understands and applies it in the same correct way. As preparation for standardization each associate analyses a number of students’ scripts. Alternative answers not already covered by the mark scheme are discussed and legislated for. If, after the standardization process, associates encounter unusual answers which have not been raised they are required to refer these to the Lead Examiner. It must be stressed that a mark scheme is a working document, in many cases further developed and expanded on the basis of students’ reactions to a particular paper. Assumptions about future mark schemes on the basis of one year’s document should be avoided; whilst the guiding principles of assessment remain constant, details will change, depending on the content of a particular examination paper. No student should be disadvantaged on the basis of their gender identity and/or how they refer to the gender identity of others in their exam responses. Physics - Mark scheme instructions to examiners 1. General The mark scheme for each question shows: • the marks available for each part of the question • the total marks available for the question • the typical answer or answers which are expected • extra information to help the Examiner make his or her judgement and help to delineate what is acceptable or not worthy of credit or, in discursive answers, to give an overview of the area in which a mark or marks may be awarded. The extra information is aligned to the appropriate answer in the left-hand part of the mark scheme and should only be applied to that item in the mark scheme. At the beginning of a part of a question a reminder may be given, for example: where consequential marking needs to be considered in a calculation; or the answer may be on the diagram or at a different place on the script. In general, the right-hand side of the mark scheme is there to provide those extra details which confuse the main part of the mark scheme yet may be helpful in ensuring that marking is straightforward and consistent. 2. Emboldening 2.1 In a list of acceptable answers where more than one mark is available ‘any two from’ is used, with the number of marks emboldened. Each of the following bullet points is a potential mark. 2.2 A bold and is used to indicate that both parts of the answer are required to award the mark. 2.3 Alternative answers acceptable for a mark are indicated by the use of or. Different terms in the mark scheme are shown by a / ; eg allow smooth / free movement. 3. Marking points 3.1 Marking of lists This applies to questions requiring a set number of responses, but for which candidates have provided extra responses. The general principle to be followed in such a situation is that ‘right + wrong = wrong’. Each error / contradiction negates each correct response. So, if the number of errors / contradictions equals or exceeds the number of marks available for the question, no marks can be awarded. However, responses considered to be neutral (often prefaced by ‘Ignore’ in the mark scheme) are not penalized. 3.2 Marking procedure for calculations Full marks can usually be given for a correct numerical answer without working shown unless the question states ‘Show your working’. However, if a correct numerical answer can be evaluated from incorrect physics then working will be required. The mark scheme will indicate both this and the credit (if any) that can be allowed for the incorrect approach. However, if the answer is incorrect, mark(s) can usually be gained by correct substitution / working and this is shown in the ‘extra information’ column or by each stage of a longer calculation. A calculation must be followed through to answer in decimal form. An answer in surd form is never acceptable for the final (evaluation) mark in a calculation and will therefore generally be denied one mark. 3.3 Interpretation of ‘it’ Answers using the word ‘it’ should be given credit only if it is clear that the ‘it’ refers to the correct subject. 3.4 Errors carried forward, consequential marking and arithmetic errors Allowances for errors carried forward are likely to be restricted to calculation questions and should be shown by the abbreviation ECF or conseq in the marking scheme. An arithmetic error should be penalized for one mark only unless otherwise amplified in the marking scheme. Arithmetic errors may arise from a slip in a calculation or from an incorrect transfer of a numerical value from data given in a question. 3.5 Phonetic spelling The phonetic spelling of correct scientific terminology should be credited (eg fizix) unless there is a possible confusion (eg diffraction/refraction) with another technical term. 3.6 Brackets (…..) are used to indicate information which is not essential for the mark to be awarded but is included to help the examiner identify the sense of the answer required. 3.7 Ignore / Insufficient / Do not allow ‘Ignore’ or ‘insufficient’ is used when the information given is irrelevant to the question or not enough to gain the marking point. Any further correct amplification could gain the marking point. ‘Do not allow’ means that this is a wrong answer which, even if the correct answer is given, will still mean that the mark is not awarded. 3.8 Significant figure penalties Answers to questions in the practical sections (7407/2 – Section A and 7408/3A) should display an appropriate number of significant figures. For non-practical sections, an A-level paper may contain up to 2 marks (1 mark for AS) that are contingent on the candidate quoting the final answer in a calculation to a specified number of significant figures (sf). This will generally be assessed to be the number of sf of the datum with the least number of sf from which the answer is determined. The mark scheme will give the range of sf that are acceptable but this will normally be the sf of the datum (or this sf -1). An answer in surd form cannot gain the sf mark. An incorrect calculation following some working can gain the sf mark. For a question beginning with the command word ‘Show that…’, the answer should be quoted to one more sf than the sf quoted in the question eg ‘Show that X is equal to about 2.1 cm’ – answer should be quoted to 3 sf. An answer to 1 sf will not normally be acceptable, unless the answer is an integer eg a number of objects. In non-practical sections, the need for a consideration will be indicated in the question by the use of ‘Give your answer to an appropriate number of significant figures’. 3.9 Unit penalties An A-level paper may contain up to 2 marks (1 mark for AS) that are contingent on the candidate quoting the correct unit for the answer to a calculation. The need for a unit to be quoted will be indicated in the question by the use of ‘State an appropriate SI unit for your answer’. Unit answers will be expected to appear in the most commonly agreed form for the calculation concerned; strings of fundamental (base) units would not. For example, 1 tesla and 1 Wb m–2 would both be acceptable units for magnetic flux density but 1 kg m2 s–2 A–1 would not. 3.10 Level of response marking instructions Level of response mark schemes are broken down into three levels, each of which has a descriptor. The descriptor for the level shows the average performance for the level. There are two marks in each level. Before you apply the mark scheme to a student’s answer read through the answer and annotate it (as instructed) to show the qualities that are being looked for. You can then apply the mark scheme. Determining a level Start at the lowest level of the mark scheme and use it as a ladder to see whether the answer meets the descriptor for that level. The descriptor for the level indicates the different qualities that might be seen in the student’s answer for that level. If it meets the lowest level then go to the next one and decide if it meets this level, and so on, until you have a match between the level descriptor and the answer. With practice and familiarity, you will find that for better answers you will be able to quickly skip through the lower levels of the mark scheme. When assigning a level, you should look at the overall quality of the answer and not look to pick holes in small and specific parts of the answer where the student has not performed quite as well as the rest. If the answer covers different aspects of different levels of the mark scheme you should use a best fit approach for defining the level and then use the variability of the response to help decide the mark within the level. i.e. if the response is predominantly level 2 with a small amount of level 3 material it would be placed in level 2. The exemplar materials used during standardization will help you to determine the appropriate level. There will be an answer in the standardizing materials which will correspond with each level of the mark scheme. This answer will have been awarded a mark by the Lead Examiner. You can compare the student’s answer with the example to determine if it is the same standard, better or worse than the example. You can then use this to allocate a mark for the answer based on the Lead Examiner’s mark on the example. You may well need to read back through the answer as you apply the mark scheme to clarify points and assure yourself that the level and the mark are appropriate. Indicative content in the mark scheme is provided as a guide for examiners. It is not intended to be exhaustive and you must credit other valid points. Students do not have to cover all of the points mentioned in the indicative content to reach the highest level of the mark scheme. An answer which contains nothing of relevance to the question must be awarded no marks. Question Answers Additional comments/Guidelines Mark AO 01.1 () 0.5(0) mm CAO  1 AO2 Question Answers Additional comments/Guidelines Mark AO 01.2 6.72 mm  tick in second box 1 AO2 Question Answers Additional comments/Guidelines Mark AO 01.3 use of ratchet with valid justification OR use of thimble and then the ratchet with valid justification  allowable ideas should focus on the possible consequences of not using the ratchet: can cause the object being measured to be distorted / squeezed / crushed / subject to excessive force or WTTE; can change the diameter / shape of the object; may lead to the reading shown being smaller than true value; damage might occur (to the mechanism); the frame (of the micrometer) might become warped; condone ‘will over-tighten (micrometer)’; condone ‘thimble used to close gap / clamp wire’ then use ratchet to tighten or WTTE + justification treat following as neutral: ‘use the thimble then the ratchet to save time’ / ‘to get accurate reading’ ‘use ratchet to make sure wire is secure’ ‘using thimble (or not using ratchet) might change the reading’ / ‘affect results’ / ‘might cause a zero error’ / ‘cause a reading below zero’ / ‘could lead to systematic error’ 1 AO1 Question Answers Additional comments/Guidelines Mark AO 01.4 0.931 use of I  1.2 OR 0.397 R  1 their I R = 0.51 (Ω) 2 for 1 allow I 2 sf rounding to 0.78 (A) OR 0.397 OR 0.397 in working 0.776 0.78 OR R  0.397 1.2 with any subject 0.931 OR use of a valid potential divider approach eg 1.2  0.931 1.2  R 0.397  0.931 for 2 condone 0.512 OR 0.5117 (Ω) 2 AO2 Question Answers Additional comments/Guidelines Mark AO 01.5 continuous ruled best-fit line drawn 1 gradient evaluated from R divided by L; with correct R  0.2 () OR correct L ≥ 150 (mm) 2 for 1 line must not pass above centre of 2nd point AND below centre of 4th point; reject hairy, thick or dashed lines if withholding mark examiner must add comment to clip 2 is for the process if using points these must lie on their line; do not penalise for AE / POT in result; expect gradient about 1.66 ( m1) withhold both marks for no line on Figure 5 2 AO2 Question Answers Additional comments/Guidelines Mark AO 01.6 d 2 R attempts to find X using  1 4 L X in range below for their metal on the answer line 2 metal resistivity /  m copper 1.6 to 1.8 (× 108) tungsten 5.4 to 5.9 (× 108) alumel 3.3 to 3.8 (× 107) nichrome 1.0 to 1.2 (× 106) POT correct and unit =  m for their metal on the answer line 3 nichrome CAO 4 for 1 expect use of their R OR the closest L value in Table 1; allow use of concordant R and d values for the L metal that is the valid choice for their R ; L d must be correct for their R ; L if value not seen in working, judge d from their X; for no 01.5 result condone the substitution of concordant R and L values for a point on Figure 5 don’t penalise for AE or POT for 2 ignore POT and use the most significant digits in their X to judge result, eg for alumel X = 0.351 scores 23 because this is equivalent to 3.51  101 allow 2 sf values that round to 2 sf in range for 3 allow alternative valid answer eg (for nichrome) 1.1 × 103  mm for 4 must be consistent with their 01.5 R L 4 1  AO3 3  AO2 Question Answers Additional comments/Guidelines Mark AO 01.7 the error bars for L / the horizontal error bars are the same length or WTTE 1 for 1 allow’ they are 10 mm’ / the width is same’; 2 AO3 any quantitative detail eg limiting values / percentage uncertainty about the horizontal error bars is neutral condone ‘bars are same’ / ‘have same range’ ‘bars are constant’ is neutral quantitative comment about the error bars for R / the vertical error bars 2 for 2 expect (about)  0.02 / (height) 0.04 () AND fifth (about)  0.04 / (height) 0.08 (); allow suitable limiting values of the error bars eg (0.)329 – (0.)371 AND (0.)614 – (0.)692; allow ‘fifth is (about) twice the length of first’ detail in an annotated sketch can earn 1 and 2 ‘bars aligned with respective axes’ / ‘bars are equidistant above / below data point’ are neutral Question Answers Additional comments/Guidelines Mark AO 01.8 idea that any two of maximum gradient, minimum gradient or mean gradient are determined using lines that pass through (all) the error bars 1 explains how to determine uncertainty in gradient 2 for 1 allow ‘measure / find gradient’ / ‘gradient can be found’; insist on idea of a line but don’t insist on ‘draw / construct’; allow mean = ‘best’, maximum = ‘steepest’ etc, maximum OR minimum = ‘worst’; ‘using the error bars’ / ‘draw line from top of first bar to bottom of last bar’ etc are neutral for 2 allow word equation or any of the following (m  m2) OR (m1  m) OR m1  m2  2 where m = mean gradient m1 = maximum gradient, m2 = minimum gradient allow ‘G’ for gradient allow ‘best gradient  worst gradient’ or vice- versa etc condone valid expressions for fractional uncertainty or for percentage uncertainty 2 AO1 Total 15