Cambridge A Level Physics 9702 — 2017 May/June Paper 3 · Variant 2

1 In this experiment, you will investigate an electrical circuit. (a) (i) Assemble the circuit shown in Fig. 1.1. 3 V V V wire B wooden strip A tape C screw Fig. 1.1 The two resistors are identical. A, B and C are crocodile clips. Connect C to the screw. (ii) Connect A to the wire at a distance p of approximately 25 cm from the screw, as shown in Fig. 1.2. (iii) Close the switch. (iv) Position B on the other side of the screw so that the two voltmeter readings have the same value V. The distance between the screw and B is q, as shown in Fig. 1.2. V V A B p q Fig. 1.2 (v) Measure and record the distances p and q. Record V. p = ....................................................... q = ....................................................... V = ....................................................... [2] (vi) Open the switch. (b) Change p and repeat (a)(iii), (a)(iv), (a)(v) and (a)(vi) until you have six sets of values of p, q and V. Record your results in a table. 1 1 Include values of and in your table. p q [10] 1 1(c) (i) Plot a graph of on the y-axis against on the x-axis. [3] q p (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 q and p are related by the equation 1 a + b = q p where a and b are constants. Use your answers in (c)(iii) to determine the values of 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)(v) Value of p in the range 20.0–30.0 cm, with unit. 1 Value of q less than p. 1 1(b) Six sets of readings of p, q and V (with correct trend and without help from Supervisor) scores 5 marks, five sets scores 4 marks etc. 5 Range: pmax ⩾ 40.0 cm and pmin ⩽ 10.0 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. 1 / p / cm–1. 1 Consistency: All values of p and q must be given to the nearest mm. 1 Significant figures: Significant figures for every value of 1 / q must be same as, or one greater than, the s.f. of q as recorded in table. 1 Calculation: Values of 1 / q calculated correctly. 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 must be plotted on the grid. Diameter of plotted points must be ⩽ half a small square (no “blobs”). Plots must be accurate to within half a small square in both x and y directions. 1 Question Answer Marks Quality: All points in the table must be plotted (at least 5) for this mark to be awarded. It must be possible to draw a straight line that is within ± 1.0 m–1 (± 0.01 cm–1) of all the plotted points in the 1 / q direction. 1 1(c)(ii) Line of best fit: Judge by 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 the full length. Allow one anomalous point only if clearly indicated (i.e. circled or labelled) 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. 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 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(d) Value of a = candidate’s gradient and value of b = candidate’s intercept. Values must not be fractions. 1 There must be no unit for a. Unit for b correct e.g. m–1 or cm–1. 1

More questions on Practical circuits

2 In this experiment, you will investigate the rotational oscillation of a combination of springs. (a) (i) You are provided with two joined springs and three joined springs. Using the two joined springs, set up the apparatus as shown in Fig. 2.1. clamp boss springs stand mass hanger h1 bench Fig. 2.1 (ii) Measure and record the height h1 of the bottom of the mass hanger above the bench, as shown in Fig. 2.1. h1 = .............................................. m [1] (iii) Add the 100 g mass to the mass hanger. Measure and record the height h2 of the bottom of the mass hanger above the bench. h2 = .............................................. m [1] (iv) Estimate the percentage uncertainty in your value of h2. percentage uncertainty = .................................................. [1] (b) (i) Calculate the spring constant k for the combination, using the expression mg k = (h 1 – h 2) where m = 0.100 kg and g = 9.81N kg–1. k = ............................................... N m–1 [1] (ii) Justify the number of significant figures you have given for your value of k. .................................................................................................................................. .................................................................................................................................. ..............................................................................................................................[1] (c) (i) Use small pieces of adhesive tape to reduce movement at the joints between components, as shown in Fig. 2.2. clamp springs tape 100 g mass mass hanger Fig. 2.2 (ii) Rotate the mass hanger and mass through one turn and release them. The masses make rotational oscillations, as shown in Fig. 2.3. Fig. 2.3 (iii) Take measurements to find the period T of the rotational oscillations. T = ............................................... s [2] (d) Repeat (a)(ii), (a)(iii), (b)(i) and (c) using the three joined springs. h1 = ................................................... m h2 = ................................................... m k = ............................................. N m–1 T = .................................................... s [3]

Mark scheme: 2(a)(ii) Value of h1 to nearest 0.1 cm. 1 h2 < h1. 1 2(a)(iv) Absolute uncertainty in h2 of 2–5 mm and correct method of calculation to obtain percentage uncertainty. If repeated readings have been taken, then the absolute uncertainty can be half the range (but not zero) if the working is clearly shown. 1 2(b)(i) Correct calculation of k. 1 2(b)(ii) Justification for s.f. in k linked to s.f. in m, g and (h1–h2) or m, g, h1 and h2. 1 2(c)(iii) Value of T in range 1.00–3.00 s. 1 Evidence of repeat readings of nT with n ⩾ 5. 1 2(d) Second values of h1 and h2. 1 Second value of T. 1 Quality: T for three springs > T for two springs. 1 2(e)(i) Two values of C calculated correctly. 1 2(e)(ii) Valid comment consistent with the calculated values of C, 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 (Difficulty) measuring h because of parallax/metre rule not vertical. C Oscillation dies away quickly/oscillation damped. D Difficult to judge/tell end of oscillation/decide when to operate stopwatch. E Other modes of oscillation occur. F Some movement at joints still occurs. 1 mark for each point up to a maximum of 4. 4 2(f)(ii) A Take more readings and plot a graph/take more readings and compare C values (not “repeat readings” on its own). B Use set square against rule (with detail)/use pointer attached to bottom of mass/use set square from rule to bottom of mass. C Twist through larger angle to get more rotations. D View (video) recording/film of motion with timer in view or put mark on mass to make it easier to see motion. E Workable method of restricting vertical/swinging movement (e.g. enclose in transparent tube). F Better method of fixing joints/use two complete springs. 1 mark for each point up to a maximum of 4. 4

More questions on Elastic and plastic behaviour