Cambridge A Level Physics 9702 — 2020 May/June Paper 3 · Variant 5

1 In this experiment, you will investigate the motion of a spring and a mass. (a) ● Set up the apparatus as shown in Fig. 1.1. boss rod of clamp z spring stand mass hanger bench Fig. 1.1 ● The distance between the top of the rod of the clamp and the bottom of the mass hanger is z, as shown in Fig. 1.1. Measure and record z. z = ............................................................... ● Add mass m to the mass hanger where m = 0.300 kg. Gently lower the mass to stretch the spring. ● Record the total added mass m (do not include the mass of the hanger). m = .......................................................... kg ● Pull the bottom of the mass hanger horizontally through a short distance. ● Release the mass hanger. The mass hanger and masses will oscillate as shown in Fig. 1.2. Fig. 1.2 ● Determine the period T of these oscillations. T = ............................................................ s [1] (b) By changing the total mass added to the mass hanger, vary m. Measure T and repeat until you have six sets of values of m and T. Include your values from (a). Do not use m = 0. T 2 1 Record your results in a table. Include values of and in your table. m m [10] T 2 1(c) (i) Plot a graph of on the y-axis against on the x-axis. [3] m m (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 T and m are related by the equation T 2 A = + B m m where A and B are constants. Using your answers in (c)(iii), determine the values of A and B. Give appropriate units. A = ............................................................... B = ............................................................... [2] (e) A student repeats the experiment using two springs in series, as shown in Fig. 1.3. Fig. 1.3 Using two springs connected in series halves the value of the spring constant of the system. Theory suggests that A is proportional to z and that B is inversely proportional to the spring constant of the system. 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) Value of T in the range 1.0–1.5 s. 1 1(b) Six sets of readings of m and time (different values) showing the correct trend and without help from the Supervisor scores 5 marks, five sets scores 4 marks etc. 5 Range: Must include m = 0.100 kg and m = 0.700 kg. 1 Column headings: Each column heading must contain a quantity, a unit and a separating mark where appropriate. The presentation of the quantity and the unit must conform to accepted scientific convention e.g. T2 / m / s2 kg–1. 1 Consistency: Raw values of time must all be given to the nearest 0.1 s or all be given to the nearest 0.01 s. 1 Significant figures: Number of s.f. for every value of 1 / m same as, or one more than, the number of s.f. in the corresponding value of m. 1 Calculation: Values of T 2 / m calculated correctly. 1 1(c)(i) Axes: Sensible scales must be 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 in the table must be plotted on the grid. Diameter of plotted points must be ⩽ half a small square. Points must be plotted to an accuracy of half a small square. 1 Quality: All observations in the table (at least 5) must be plotted on the grid. Trend of points must be correct. It must be possible to draw a straight line that is within 0.5 kg–1 on the 1 / m 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 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. Line 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 Δx / Δy. 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 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 A = candidate’s gradient and value of B = candidate’s intercept. The values must not be fractions. 1 Unit for A correct (s2) and unit for B correct (s2 kg–1). 1 1(e) Line W drawn with larger gradient and larger y-intercept. 1

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2 In this experiment, you will investigate a potential divider circuit. (a) (i) ● Connect the voltmeter across the cell as shown in Fig. 2.1. V Fig. 2.1 ● The reading on the voltmeter is the electromotive force (e.m.f.) E of the cell. Record E. E = ............................................................... ● Measure and record the diameter d of wire A. d = ............................................................... [1] (ii) Calculate Ed 2. Ed 2 = ......................................................... [1] (iii) Justify the number of significant figures that you have given for your value of Ed 2. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (b) (i) You have been provided with a wooden strip with some wire connected between two nails. ● Set up the circuit shown in Fig. 2.2. wooden wire strip nail C D V wire A Fig. 2.2 ● C and D are crocodile clips. Place the clips on wire A so that the length L of wire between C and D is equal to the length of wire between the two nails. ● Measure and record L. L = ......................................................... [1] (ii) Estimate the percentage uncertainty in your value of L. Show your working. percentage uncertainty = ......................................................... [1] (c) ● Close the switch. ● Record the voltmeter reading V. V = ............................................................... ● Open the switch. ● Remove the wire between C and D. [1] (d) ● Measure and record the diameter d of wire B. d = ............................................................... ● Calculate Ed 2. Ed 2 = ............................................................... ● Connect length L of wire B between C and D and repeat (c). V = ............................................................... [3]

Mark scheme: 2(a)(i) Value of d in the range 0.22–0.25 mm 1 2(a)(ii) Correct calculation of Ed 2. 1 2(a)(iii) Justification for s.f. in Ed 2 linked to s.f. in E and d. 1 2(b)(i) Value of L in the range 48.0–52.0 cm with unit. 1 2(b)(ii) Percentage uncertainty in L based on absolute uncertainty of 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(c) Value of V to the nearest 0.001 V with unit in the range 0.5–1.0 V. 1 2(d) Second value of d. 1 Second value of V. 1 Quality: Second value of V < first value of V. 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 stated by the candidate. 1 2(f) Correct calculation of D with value between candidate’s d values. 1 Question Answer Marks 2(g)(i) A Two readings are not enough to draw a (valid) conclusion (not “not enough for accurate results”, “few readings”). B Clips slide on wire. C Contact poor between clip and (thinnest) wire. D Resistance of wires and internal resistance of cell may distort results. E Difficult to measure L with reason related to wire e.g. kinks/not straight. F Difficult to measure length of wire on wooden strip e.g. nails obstruct measurement. 1 mark for each point up to a maximum of 4. 4 2(g)(ii) A Take more readings and plot a graph or take more readings and compare k values (not “repeat readings” on its own). B Improved method of gripping e.g. screw clips to wire. C Use thicker wires/improved method to improve contact with (thinnest) wire e.g. solder connections. D Monitor p.d. across cell/use shorter connecting wires. E Solder wires A and B to (different) nails (to ensure wires are straight). F Improved method e.g. use longer wire and attach clips/use nails with smaller heads. 1 mark for each point up to a maximum of 4. 4

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