Cambridge A Level Physics 9702 — 2018 May/June Paper 3 · Variant 3

1 In this experiment, you will investigate an electrical circuit. (a) • Set up the circuit shown in Fig. 1.1. 1.5 V wooden strip x wire F G R R V V V1 V2 Fig. 1.1 F and G are crocodile clips. • Place G on the wire so that the distance x between the ends of F and G is approximately 40 cm. • Measure and record x. x = ............................................................... • Close the switch. • Record the voltages V1 and V2. V1 = ............................................................... V2 = ............................................................... • Open the switch. [2] (b) Vary x until you have six sets of readings of x, V1 and V2. V1 Record your results in a table. Include values of (V2–V1) and in your table. x [10] V1(c) (i) Plot a graph of (V2–V1) on the y-axis against on the x-axis. [3] x (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 V2, V1 and x are related by the equation PV1 (V2–V1) = + Q x where P and Q are constants. Using your answers in (c)(iii), determine values for P and Q. Give appropriate units. P = ............................................................... Q = ............................................................... [2] [Total: 20] You may not need to use all of the materials provided.

Mark scheme: 1(a) Values of V1 and V2 with units and to the nearest 0.01 V. 1 |V2 | > |V1|. 1 1(b) Six sets of readings of x, V1 and V2 (different values) showing the correct trend and without help from the Supervisor scores 5 marks, five sets scores 4 marks etc. 5 Range: xmin ⩽ 10.0 cm and xmax ⩾ 70.0 cm. 1 Column headings: Each column heading must contain a quantity and a unit where appropriate. The presentation of quantity and unit must conform to accepted scientific convention e.g. (V1 / x) / V m–1. 1 Consistency: All values of x must be given to the nearest mm. 1 Significant figures: All values of V1 / x must be given to 2 or 3 s.f. 1 Calculation: Values of V1 / x 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 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 points in the table must be plotted on the grid for this mark to be awarded. It must be possible to draw a straight line that is within 0.040 on the (V2 – V1) axis of all plotted points. 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). 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 by the candidate. Line must not be kinked or thicker than half a small square. 1 1(c)(iii) Gradient: The hypotenuse of the triangle used should 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 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 P = candidate’s gradient and value of Q = candidate’s intercept. The values must not be fractions. 1 Unit for P correct (e.g. m or cm or mm) and unit of Q correct (e.g. V) unless zero. 1

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2 In this experiment, you will investigate the motion of an interrupted pendulum. (a) Set up the apparatus as shown in Fig. 2.1. split cork clamp boss string L stand bob bench Fig. 2.1 • Adjust the string in the split cork so that the distance L between the bottom of the split cork and the centre of the bob is approximately 55 cm. • Measure and record L. L = ............................................................... L • Calculate . 2 L = ............................................................... 2 [1] (b) (i) • Attach the other boss and clamp and the wooden rod to the stand as shown in Fig. 2.2. • Adjust the position of the wooden rod so that, when the string is touching the rod, the angle A between the vertical and the string is approximately 14°, as shown in Fig. 2.2. • Without changing the length of the pendulum, ensure the distance between the L wooden rod and the centre of the bob is . 2 A wooden rod clamp boss L 2 bench Fig. 2.2 • Measure and record angle A. A = ...........................................................[1] (ii) Estimate the percentage uncertainty in your value of A. percentage uncertainty = ...........................................................[1] (c) (i) • Pull the bob away from the wooden rod so that the angle between the string and the vertical is 45°, as shown in Fig. 2.3. 45° wooden rod bench Fig. 2.3 • Release the bob. The bob will oscillate and hit the wooden rod. • Determine the period T of these oscillations. T = ...........................................................[2]

Mark scheme: 2(a) Value of L to the nearest mm with unit and in range 50.0–60.0 cm. 1 2(b)(i) Value of A to the nearest degree with unit and in the range 11–17°. 1 2(b)(ii) Percentage uncertainty in A based on absolute uncertainty of 2°–5°. 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(c)(i) Value of T in the range 1.20–1.60 s with unit. 1 Evidence of at least two sets of nT where n ⩾ 5. 1 2(c)(ii) Correct calculation of d. 1 2(c)(iii) Justification for s.f. in d linked to s.f. in A (or measured angle). 1 2(d) Second value of A. 1 Second value of T. 1 Quality: second value of T > first value of T. 1 2(e)(i) Two values of k calculated correctly. 1 2(e)(ii) Valid comment consistent with calculated values of k, testing against a criterion specified by the candidate. 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 measure L with reason e.g. locating centre of bob/parallax/bob or cork gets in the way of the ruler. C Difficult to measure A or 45° or angle with a reason e.g. no indication of vertical/hard to hold and measure from protractor/hard to hold protractor steady/string too thick/parallax error. D Problem with bob moving between setting and releasing. E Difficulty setting rod at L / 2 with reason e.g. setting rod and angle at the same time/rod moves when tightening the clamp/rod moves when pendulum hits. F Difficulty in judging start/end of oscillation. 1 mark for each point up to a maximum of 4. 4 2(f)(ii) A Take many readings (for different values of A) and plot a graph or take more values of k and compare (not “repeat readings” on its own). B Improved method of measuring L e.g. measure diameter and add on (or take away) radius from length of string from cork to top (bottom) of bob, or e.g. clear use of pointer(s). C Improved method of measuring angle e.g. use a plumb line/clamp protractor/use thinner string, or e.g. shadow projection ideas/photograph and measure angle. D Improved mechanism of releasing the bob e.g. clamp bob/use a card gate/add a stop. E Mark string. F Method of improving timing e.g. put a marker anywhere except at the ends/video with timer (or replay frame by frame). 1 mark for each point up to a maximum of 4. 4

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