Cambridge A Level Physics 9702 — 2017 May/June Paper 3 · Variant 1

1 In this experiment, you will investigate an electrical circuit. (a) Set up the circuit shown in Fig. 1.1. power supply A metre rule wire x crocodile crocodile clip clip Fig. 1.1 The distance x between the crocodile clips should be approximately 40 cm. (b) (i) Measure and record x. x = ...................................................... (ii) Close the switch. (iii) Record the ammeter reading I1. I1 = ..................................................[1] (iv) Open the switch. (c) (i) Connect an additional lead L to the circuit as shown in Fig. 1.2. A L x Fig. 1.2 (ii) Close the switch. (iii) Record the ammeter reading I2. I2 = ..................................................[1] (iv) Open the switch. (v) Remove L. The circuit is now as shown in Fig. 1.1. (d) Increase x and repeat (b) and (c) until you have six sets of readings of x, I1 and I2. I2 Record your values in a table. Include values of in your table. I1 [10] I2(e) (i) Plot a graph of on the y-axis against x on the x-axis. [3] I1 (ii) Draw the straight line of best fit. [1] (iii) Determine the gradient and y-intercept of this line. gradient = ...................................................... y-intercept = ...................................................... [2] (f) It is suggested that the quantities I1, I2 and x are related by the equation I2 = Px + Q I1 where P and Q are constants. Using your answers in (e)(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(b)(iii) 1 1(c)(iii) I2 > I1 (ECF unit from 1(b)(iii)). 1 1(d) Six sets of readings of x (different values), I1, I2 with correct trend and without help from Supervisor scores 5 marks, five sets scores 4 marks etc. 5 Range: xmax ⩾ 90 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. x / m, I2/ mA, I2/ I1 no unit. 1 Consistency: All values of x must be given to the nearest mm. 1 Significant figures: All values of I2 / I1 must be given to the same number of s.f. as (or one more than) the s.f. in raw I1 and I2 (using the s.f. of the I value with the lowest number of s.f.). 1 Calculation: Values of I2/ I1 are correct. 1 1(e)(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 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 Question Answer Mark Quality: All values of I2 / I1 must be greater than 1. All points in the table must be plotted for this mark to be awarded. It must be possible to draw a straight line that is within ± 0.05 on the I2/ I1 axis (normally y axis) of all plotted points. 1 1(e)(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 (i.e. circled or labelled) by the candidate. There must be at least five points left after the anomalous point is disregarded. Lines must not be kinked or thicker than half a small square. 1 1(e)(iii) Gradient: Gradient sign on answer line matches graph drawn. The hypotenuse of the triangle used must be greater than half the length of the drawn line. 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. 1 y-intercept: Correct read-off from a point on the line substituted correctly into y = mx + c or an equivalent expression. Read-off 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 in y direction. 1 1(f) Value of P = candidate’s gradient and value of Q = candidate’s intercept. The values must not be fractions. 1 Unit for P is correct (e.g. m–1) and Q stated without a unit. 1

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2 In this experiment, you will investigate the motion of oscillating table tennis balls. (a) Tape each ball to a length of string. Ensure the total length of the string and ball is 35.0 cm, as shown in Fig. 2.1. ball string tape 35.0 cm Fig. 2.1 (b) (i) Set up the apparatus as shown in Fig. 2.2. wooden rod boss boss strings stand stand balls bench Fig. 2.2 (ii) Pull one of the balls towards you through a short distance. Release the ball and determine the time for five complete oscillations. time = ................................................... s Repeat for the other ball. time = ................................................... s [1] (iii) Remove the balls and strings from the wooden rod. (c) (i) Tape the shorter wooden block to one of the balls as shown in Fig. 2.3. Tape should be used on opposite sides of the block and the ball. wooden block mark tape x Fig. 2.3 The distance between the end of the string loop and the mark around the wooden block is x. (ii) Measure and record x. x = ..................................................[1] (iii) Estimate the percentage uncertainty in your value of x. percentage uncertainty = ..................................................[1] (d) (i) Set up the apparatus as shown in Fig. 2.4. Fig. 2.4 (ii) Pull both balls towards you. Release the balls at the same time and watch the movement. The two balls will move backwards and forwards becoming out of phase. After a time they will be back in phase so that they move towards you together. The ball with the block attached completes n oscillations in this time.

Mark scheme: 2(b)(ii) Values of time in the range 3–7 s and within 0.4 s of each other. All raw readings stated to same precision and to at least 0.1 s. 1 2(c)(ii) x on the answer line in the range 35.0–40.0 cm and all value(s) of raw x to nearest mm with unit. 1 2(c)(iii) Absolute uncertainty in x in range 2–5 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(e)(i) Value of n on answer line in the range 10 to 20. No unit. 1 Evidence of repeat readings. 1 2(e)(ii) Correct calculation of (n + 1)2 / n2. 1 2(f) Second value of x. 1 Second value of n. 1 Quality: second value of n < first value of n (if x2 < x1 allow n2 > n1). 1 2(g)(i) Two values of k calculated correctly. 1 2(g)(ii) Valid comment consistent with calculated values of k, testing against a criterion specified by the candidate. 1 2(h) Correct calculation of L written to 3 s.f. and correctly rounded to 3 s.f. 1 Question Answer Mark 2(i)(i) A Two readings are not enough to draw a valid conclusion (not “not enough for accurate results”, “few readings”). B Difficult to judge when the balls are back in phase. C Balls hit each other/blown by moving air/balls move sideways/irregular movement. D Difficult to ensure both lengths 35 cm or difficult to measure x with a reason e.g. string kinked/parallax error. E Damping/oscillations die out quickly. F Difficulty linked to fixing block/wood with reason e.g. longer block requires more tape (therefore an unfair test)/block comes unstuck/blocks attached at an angle (x not constant). G For two/both balls the release point is different or release instant is different. 1 mark for each point up to a maximum of 4. 4 2(i)(ii) A Take more readings and plot a graph/take more readings and compare k values (not “repeat readings” on its own). B Video/film/record and perpendicular to plane of oscillation/from the side. C Turn off air conditioning/close windows/use windshield/use a longer rod. D Improved method of measuring 35 cm or x e.g. use clamps to fix loop and ball. F Improved method of attachment e.g. Blu-Tack/glue/Velcro/stickier tape/stronger adhesive on the tape. G Improved method of release e.g. bar to hold both balls then drop away like a gate. 1 mark for each point up to a maximum of 4. 4

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