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CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 2015 series

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CAMBRIDGE INTERNATIONAL EXAMINATIONS Cambridge International Advanced Subsidiary and Advanced Level MARK SCHEME for the October/November 2015 series 9702 PHYSICS 9702/35 Paper 3 (Advanced Practical Skills 1), maximum raw mark 40 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 will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 2015 series for most Cambridge IGCSE®, Cambridge International A and AS Level components and some Cambridge O Level components. ® IGCSE is the registered trademark of Cambridge International Examinations. Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9702 35 1 (b) (i) Value of a with consistent unit and in the range 0 to 50.0 cm. [1] (v) Value of V with unit to nearest 0.001 V and in range 0 to 2 V. [1] (c) Six sets of readings of a, b and V scores 5 marks, five sets scores 4 marks etc. [5] Incorrect trend –1. Minor help from Supervisor –1. Major help from Supervisor –2. Range: [1] amax – amin ⩾ 30.0 cm. Column headings: [1] Each column heading must contain a quantity and a unit. The presentation of quantity and unit must conform to accepted scientific convention. e.g. a / m or a (m), 1/V / V–1. Consistency: [1] All values of a and b must be given to the nearest mm. Significant figures: [1] Every value of 1 / V must be given to the same number of significant figures as (or one more than) the number of significant figures in the corresponding value of V. Calculation: [1] Values of 1 / V calculated correctly to the number of significant figures given by the candidate. (d) (i) Axes: [1] Sensible scales must be used. Awkward scales (e.g. 3:10) are not allowed. Scales must be chosen so that the plotted points occupy at least half the graph grid in both x and y directions. Scales must be labelled with the quantity that is being plotted. Scale markings should be no more than three large squares apart. Plotting: [1] All observations in the table must be plotted on the grid. Diameter of plotted points must be ⩽ half a small square (no “blobs”). Points must be plotted to an accuracy of half a small square. Quality: [1] All points in the table must be plotted (at least 5) for this mark to be awarded. Scatter of points must be no more than ± 0.050 m (5.0 cm) to scale in the b direction from a straight line. (ii) Line of best fit: [1] Judge by balance of all points on the grid about the candidate’s line (at least 5 points). There must be an even distribution of points either side of the line along the full length. Allow one anomalous point only if clearly indicated (i.e. circled or labelled) by the candidate. Lines must not be kinked or thicker than half a square. © Cambridge International Examinations 2015 Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9702 35 (iii) Gradient: [1] The hypotenuse of the triangle must be greater than half the length of the drawn line. Do not allow ∆x / ∆y. Sign of gradient must match graph drawn. Both read-offs must be accurate to half a small square in both the x and y directions. y-intercept: [1] Either: Correct read-off from a point on the line substituted into y = mx + c or an equivalent expression. Read-offs must be accurate to half a small square in both x and y directions. Or: Intercept read directly from the graph, with read-off accurate to half a small square. (e) Value of P = candidate’s gradient and value of Q = candidate’s intercept. [1] Unit for P is correct (e.g. m–1 V–1) and unit for Q is correct (e.g. V–1). [1] 2 (b) (iv) All values of x with unit to nearest mm. Average x ⩽ 20.0 cm. [1] (c) (i) Value of θ to the nearest degree in the range 25° to 35°. [1] (ii) Absolute uncertainty in θ in range 2° to 5° and correct method of calculation to obtain percentage uncertainty. If repeated readings have been taken, then the absolute uncertainty can be half the range (but not zero) if working is clearly shown. [1] (iii) Correct calculation of cos2(θ / 2). No unit. [1] (iv) Justification for significant figures in cos2(θ / 2) linked to significant figures in θ. [1] (d) (ii) T in range 0.5 s to 2.5 s, with unit. [1] Evidence of repeat readings of T. [1] (f) Second value of θ. [1] Second values of T1 and T2. [1] Second value of T1 / T2 first value of T1 / T2 when rounded to 2 s.f. [1] (g) (i) Two values of k calculated correctly. [1] (ii) Valid comment consistent with the calculated values of k, testing against a criterion specified by the candidate. [1] © Cambridge International Examinations 2015 Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2015 9702 35 (h) (i) Limitations (4 max.) (ii) Improvements (4 max.) Do not credit A Not enough readings to draw a Take more readings and plot a Few readings/ conclusion graph/ only one reading/ obtain more k values and not enough readings compare for an accurate result/ “repeat readings” on its own/ take more readings and (calculate) average k B Difficult to measure θ or read Improved method of measuring Just “difficult to protractor with reason e.g. rod is θ e.g. shadow projection with measure θ”/ above protractor/rod obscures view light above/thinner rod/rod with smaller rod/ smaller diameter/plumb-lines “protractor reads to hung from rod/larger 1°” protractor/360° protractor C Oscillations or T affected by... Improved method of release e.g. Release by e.g. air movement card gate electromagnet/ force on release or cutting string/ different forces switch off air conditioning/close damping/ angle of release windows/closed room air resistance/ unwanted modes of oscillation friction D Large percentage uncertainty in Valid method to improve timing Oscillations too fast/ time/period T is short e.g. use video with timer/frame high/low speed by frame/motion sensor and camera/ position at side of cradle video on its own/ or human reaction time/ Increase T by... e.g. heavier just “difficult to nail/longer nail/string determine time”/ fiducial marker E Valid problem linked to magnetism Valid method to overcome Nail loses magnetism e.g. nail weakly magnetised/metal problem linked with magnetism stand attracts nail/interference by e.g. stroke nail more times/use Earth’s magnetic field. of coil F Method of fixing Just “stick paper” paper/protractor/magnets e.g. without method tape/Blu-tack/draw protractor on paper © Cambridge International Examinations 2015

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