Cambridge A Level Physics 9702 — 2019 May/June Paper 3 · Variant 5

1 In this experiment, you will investigate an electrical circuit. (a) (i) You have been provided with two metre rules. One is labelled P and the other is labelled Q. • Set up the circuit shown in Fig. 1.1. A d rule P F H tape wire rule Q J G c Fig. 1.1 • F, G, H and J are crocodile clips. Place H approximately half-way along the wire on rule P. • The distance between F and H is d, as shown in Fig. 1.1. Record d. d = ............................................................... • Place J on the wire on rule Q so that the distance between G and J is approximately 60 cm. The distance between G and J is c, as shown in Fig. 1.1. • Record c. c = ............................................................... c – d • Calculate n, where n = . d n = ............................................................... [1] (ii) • Close the switch. • Record the ammeter reading I. I = ............................................................... • Open the switch. [1] (b) Keeping d constant, vary c until you have six sets of readings of c and I. Do not use values of c less than d. (n + 2) Record your results in a table. Include values of n and in your table. (n + 1) [9] (n + 2)(c) (i) Plot a graph of I on the y-axis against on the x-axis. [3] (n + 1) (ii) Draw the straight line of best fit. [1] (iii) Determine the gradient and y-intercept of this line. gradient = ............................................................... y-intercept = ............................................................... [2] (d) It is suggested that the quantities I and n are related by the equation (n + 2) I = S + T (n + 1) where S and T are constants. Using your answers in (c)(iii), determine values for S and T. Give appropriate units. S = ............................................................... T = ............................................................... [2] (e) Theory suggests that S is inversely proportional to d and that T is independent of d. The experiment is repeated using the same equipment but a larger value of d. For this experiment, draw a second line on the graph to show the expected results. Label this line W. [1] [Total: 20] You may not need to use all of the materials provided.

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 marks, five sets scores 4 marks etc. 5 Range: Includes a reading of c ⩾ 95.0 cm and no values of c < d. 1 Column headings: 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. 1 Consistency: All values of c must be given to the nearest mm only. 1 Calculation: Values of (n + 2) / (n + 1) are correct. 1 1(c)(i) Axes: 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. 1 Plotting of points: 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. 1 Quality: 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 Question Answer Marks 1(c)(ii) Line of best fit: 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 1(c)(iii) Gradient: 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. 1 y-intercept: 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 1(d) Value of S = candidate’s gradient and value of T = candidate’s intercept. The values must not be fractions. 1 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

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2 In this experiment, you will investigate the oscillations of a pendulum. (a) • Set up the apparatus as shown in Fig. 2.1. small pieces of wood held in clamps boss x stand L1 L1 L2 string A B wooden strip bob bench Fig. 2.1 • The distance between the strings supporting the wooden strip is x. The distances between the top of the strip and the bottom of the small pieces of wood should be equal. These distances are both L1. The distance between the centre of the bob and the bottom of the small pieces of wood is L2. Adjust the position of the strings so that x ≈ 25 cm, L1 ≈ 25 cm and L2 ≈ 45 cm. • The strings should be vertical, the strip should be parallel to the bench and the strip should be supported centrally by the strings. Measure and record x and L1. x = ......................................................... cm L1 = ......................................................... cm [2] (b) (i) • Pull the bob and end B of the strip towards you through a short distance. • Release the bob and the strip together so that they oscillate. • Adjust L2 until the periods of the oscillations of the bob and of the strip are the same. • Measure and record L2. L2 = ................................................... cm [1] (ii) Estimate the percentage uncertainty in your value of L2. percentage uncertainty = ......................................................... [1] L1 . (iii) Calculate L2 L1 = ......................................................... [1] L2 L1 (iv) Justify the number of significant figures that you have given for your value of . L2 ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (c) • Change x to approximately 30 cm and L1 to approximately 20 cm. • The strings should be vertical, the strip should be parallel to the bench and the strip should be supported centrally by the strings. Measure and record x and L1. x = ..........................................................cm L1 = ..........................................................cm • Repeat (b)(i) and (b)(iii). L2 = ..........................................................cm L1 = ............................................................... L2 [3]

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. 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. 1 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 Question Answer Marks 2(f)(i) A Two readings are not enough to draw a (valid) conclusion (not “not enough for accurate results”, “few readings”). 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. 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). 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. 4

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