Cambridge A Level Physics 9702 — 2019 Oct/Nov Paper 3 · Variant 1

1 In this experiment, you will investigate an electrical circuit. (a) • Place the 10 Ω resistor in component holder P. • Place the 22 Ω resistor in component holder Q. • Set up the circuit shown in Fig. 1.1. d metre rule wire K L Q P V Fig. 1.1 • K and L are crocodile clips. The resistor in component holder Q has resistance R. Place L approximately half-way along the wire. • The distance between K and L is d, as shown in Fig. 1.1. Record R and d. R = ............................................................... d = ............................................................... • Close the switch. • Record the voltmeter reading V. V = ............................................................... • Open the switch. [1] (b) • Change the resistor in Q. Do not change the resistor in P. • Record the new value of R. R = ............................................................... • Close the switch. • Change the position of L on the wire so that the voltmeter reading is as close as possible to the value for V in (a). • Record d. d = ............................................................... • Open the switch. [1] (c) • Write down your value of V from (a). V = ............................................................... • Repeat (b) until you have six sets of readings of R and d. Include your readings from (a) and (b). R Record your results in a table. Include values of in your table. d [10] R(d) (i) Plot a graph of on the y-axis against R on the x-axis. [3] d (ii) Draw the straight line of best fit. [1] (iii) Determine the gradient and y-intercept of this line. gradient = ............................................................... y-intercept = ............................................................... [2] (e) It is suggested that the quantities R and d are related by the equation R = AR + B d where A and B are constants. Using your answers in (d)(iii), determine values for A and B. Give appropriate units. A = ............................................................... B = ............................................................... [2] [Total: 20] You may not need to use all of the materials provided.

Mark scheme: 1(a) 1 1(b) Value of d with unit and in the range 20.0–90.0 cm. 1 1(c) Six sets of readings of R and d (different values) showing the correct trend and without assistance from the Supervisor scores 5 marks, five sets scores 4 marks etc. 5 Range: Values of R must include 12 Ω and 39 Ω. 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. d / m and R / Ω and R / d / Ω m–1. 1 Consistency: All values of d must be given to the nearest mm. 1 Significant figures: All values of R / d must be given to either 2 or 3 s.f. 1 Calculation: Values of R / d are correct. 1 1(d)(i) Axes: Sensible scales are used, no awkward scales (e.g. 3:10). 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 must be plotted on the grid. Diameter of plotted point must be ⩽ half a small square. Points must be plotted to an accuracy of half a small square. 1 Quality: All points in the table (at least 5) must be plotted on the grid for this mark to be awarded. Trend of points on graph must be positive. All points must be within 2.5 Ω on the R-axis of a straight line. 1 Question Answer Marks 1(d)(ii) Line of best fit: Judge by the balance of all points on the grid (at least 5) about the candidate’s line. There must be an even distribution of points either side of the line along its full length. One anomalous point is allowed only if clearly indicated (i.e. circled or labelled) by the candidate. There must be at least 5 points left after the anomalous point is disregarded. Line must not be kinked or thicker than half a square. 1 1(d)(iii) Gradient: The hypotenuse of the triangle used should be greater than half the length of the drawn line. Both read-offs must be accurate to half a small square in both the x and y directions. The sign of the gradient on the answer line must match the graph. Method of calculation must be correct, e.g. not ∆x / ∆y. 1 y-intercept: Correct read-off from a point on the line substituted into y = mx + c or an equivalent expression. 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 R = 0, accurate to half a small square in the R direction. 1 1(e) Value of A = candidate’s gradient and value of B = candidate’s intercept. The values must not be fractions. 1 Unit for A is correct (e.g. m–1 or cm–1 or mm–1) and unit for B is correct (e.g. Ω m–1 or Ω cm–1 or Ω mm–1). 1

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2 In this experiment, you will investigate the motion of two pendulums. (a) (i) You have been provided with two pendulums. • Set up the apparatus using the pendulum that has a loop of string at the end, as shown in Fig. 2.1. upper wooden rod boss loop of string L0 stand lower wooden rod x boss bob bench Fig. 2.1 • The distance between the bottom of the lower wooden rod and the centre of the bob is x. The distance between the bottom of the upper wooden rod and the centre of the bob is L0. Adjust the position of the lower wooden rod until x is approximately 10 cm. • Measure and record x and L0. x = ............................................................... L0 = ............................................................... [1] (ii) Estimate the percentage uncertainty in your value of x. percentage uncertainty = ......................................................... [1] (b) (i) • Set up a second pendulum as shown in Fig. 2.2. clamp split cork boss L Fig. 2.2 • The distance between the bottom of the split cork and the centre of the bob is L. Adjust the string in the split cork until L is approximately 30 cm. • Pull both bobs towards you through a short distance. • Release the bobs at the same time. The oscillations of the bobs will be out of phase. • Adjust L so that the oscillations of the bobs remain in phase for several cycles after release. • Measure and record L. L = ......................................................... [1] (ii) Calculate L. L = ......................................................... [1] (iii) Justify the number of significant figures that you have given for your value of L. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (c) • Adjust the position of the lower wooden rod until x is approximately 35 cm. • Measure and record x. x = ............................................................... • Repeat (b)(i) and (b)(ii). L = ............................................................... L = ............................................................... [3]

Mark scheme: 2(a)(i) Value of x to the nearest mm with unit in the range 9.0–11.0 cm. 1 2(a)(ii) Percentage uncertainty in x based on absolute uncertainty of 2–4 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)(i) Value of raw L to the nearest mm with unit and in the range 20.0–30.0 cm. 1 2(b)(ii) Correct calculation of L . 1 2(b)(iii) Justification for s.f. in L linked to s.f. in L. 1 2(c) Second value of x. 1 Second value of L. 1 Quality: Second value of L > first value of L. 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)(i) Value of T in the range 1.0–2.0 s. 1 2(e)(ii) Correct calculation of g with correct consistent unit using second value of k. 1 Question Answer Marks 2(f)(i) A Too few readings/(only) two readings not enough to draw a (valid) conclusion (not ‘not enough for accurate results’, ‘few readings’). B Difficult to determine x or L0 or L with reason e.g. parallax error/locating centre of bob/lower curved edge of wooden rod/holding ruler by hand. C Difficult to release two bobs at same instant/time. D Pendulums have different amplitudes/displacements or Two oscillations have different motions so difficult to compare. E Difficult to judge when the two pendulums are exactly in phase/difficult to adjust to the exact length so that the pendulums are in phase/trial and error process needed to identify when length gives same phase. F Difficult to judge start of/end of/complete oscillation. 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 Measure to top and bottom of ball and take average or Take string off and measure on table or Clamp a ruler (vertically). C Improved method of release e.g. card gate release. E Use stop-watch and test for same period for each pendulum. F Video/record/film and view with timer/frame-by-frame. 1 mark for each point up to a maximum of 4. There is no marking point labelled D. 4

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