Physics 9702/35 May/June 2019: question paper and mark scheme

Mark scheme

1(a)(i) Value of c in the range 55.0–65.0 cm with unit. 1 1(a)(ii) Value of I in the range 75.0–175.0 mA with unit. 1 1(b) Six sets of readings of c and I (different values) showing the correct trend and without help from the Supervisor scores 5 5 marks, five sets scores 4 marks etc. Range: Includes a reading of c ⩾ 95.0 cm and no values of c < d. 1 Column headings: 1 Each column heading must contain a quantity, a unit and a separating mark where appropriate. There should be no units for the n or (n + 2) / (n + 1) columns. The presentation of the quantity and unit must conform to accepted scientific convention e.g. c / m. Consistency: 1 All values of c must be given to the nearest mm only. Calculation: 1 Values of (n + 2) / (n + 1) are correct. 1(c)(i) Axes: 1 Sensible scales must be used, no awkward scales (e.g. 3:10 or fractions). 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 correctly labelled with the quantity that is being plotted. Scale markings should be no more than three large squares apart. Plotting of points: 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 observations in the table (at least 4) must be plotted on the grid. Trend of points on graph must be correct. It must be possible to draw a straight line that is within ±0.05 (to scale) of all the plotted points on the (n + 2) / (n + 1) axis. 1(c)(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. If there are 6 or more points, allow one anomalous point only if clearly indicated by the candidate. Lines must not be kinked or thicker than half a small square. 1(c)(iii) Gradient: 1 The hypotenuse of the triangle used must be greater than half the length of the drawn line. The method of calculation must be correct. Do not allow ∆x / ∆y. Both read-offs must be accurate to half a small square in both the x and y directions. Sign of gradient must match graph. y-intercept: 1 Correct read-off from a point on the line and substituted into y = mx + c. Read-off must be accurate to half a small square in both x and y directions. or Intercept read directly from the graph with read-off at x = 0, accurate to half a small square. 1(d) Value of S = candidate’s gradient and value of T = candidate’s intercept. 1 The values must not be fractions. Unit for S and T correct (mA or A). 1 1(e) Correct line W with smaller gradient and below the original line (with a smaller intercept if false origin). 1

Mark scheme

2(a) Raw values of x and L1 to the nearest mm. 1 Mean values of x and L1 in the range 23.0–27.0 cm. 1 2(b)(i) Values of L2 in the range 40.0–50.0 cm. 1 2(b)(ii) Percentage uncertainty in L2 based on absolute uncertainty of 2–10 mm. 1 If repeated readings have been taken, then the uncertainty can be half the range (but not zero) if the working is clearly shown. Correct method of calculation to obtain percentage uncertainty. 2(b)(iii) Correct calculation of L1 / L2. 1 2(b)(iv) Justification for s.f. in L1 / L2 linked to s.f. in L1 and L2. 1 2(c) Second values of x and L1. 1 Second value of L2. 1 Quality: Second value of L2 < first value of L2. 1 2(d)(i) Two values of k calculated correctly. 1 2(d)(ii) Valid comment consistent with calculated values of k, testing against a criterion stated by the candidate. 1 2(e) Correct calculation of l with a consistent unit. 1 2(f)(i) A Two readings are not enough to draw a (valid) conclusion (not “not enough for accurate results”, “few readings”). 4 B Difficult to get the lengths the same with reason e.g. judging the strip horizontal, checking the strings vertical, adjusting the setup. C Difficult to determine lengths with a reason e.g. cannot place rule alongside strings, difficult to hold the ruler still, holding ruler with hands, parallax error, difficult to locate centre of bob. D Difficulty with oscillations of rule e.g. have small amplitude, unwanted modes, strings move along during oscillation, stands move, oscillations die away quickly. or Difficult to ensure that x straddles centre of the strip equally. E Difficult to see when both oscillations match their periods. F Releasing bob and rule simultaneously is difficult/uneven force may be applied. 1 mark for each point up to a maximum of 4. 2(f)(ii) A Take more readings and plot a graph or take more readings and compare k values (not “repeat readings” on its own). 4 B Detailed use of spirit level/plumb line/set squares. C Mark strings or use a clamped rule/pointer on rule with detail. D Clamp stand to bench/method of attaching string to strip. or Attach/mark scale onto strip or mark centre of strip. E Use longer dimensions (to increase period)/use a video to identify when in phase/use a timer and check individually. F Use a card for a gate for both to release together. 1 mark for each point up to a maximum of 4.