Cambridge A Level Physics 9702 — 2022 May/June Paper 3 · Variant 3

1 In this experiment, you will investigate an electrical circuit. You have been provided with a wooden strip with a wire attached. (a) Measure and record the length L of the wire between the nails on the wooden strip, as shown in Fig. 1.1. nail wooden strip wire nail L Fig. 1.1 L = ......................................................... [1] (b) You have also been provided with a wire labelled A with crocodile clips at its ends. ● Set up the circuit shown in Fig. 1.2. 1.5 V d.c. Y wire A wooden strip G H J F d V V V1 V2 Fig. 1.2 ● F, G, H and J are crocodile clips. The distance between one of the nails and H is d, as shown in Fig. 1.2. Attach H to the wire on the wooden strip so that d is approximately 20 cm. ● Close the switch. ● Record the value of d and the voltmeter readings V1 and V2. d = ............................................................... V1 = ............................................................... V2 = ............................................................... ● Open the switch. [2] (c) Increase d by placing H at different positions on the wire and record V1 and V2. Repeat until you have six sets of readings of d, V1 and V2. Include your values from (b). V2 2 Record your results in a table. Include values of and d in your table. ( V1)d [8] V2 2(d) (i) Plot a graph of on the y-axis against d on the x-axis. [3] ( V1)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 V1, V2 and d are related by the equation V2 2 = Pd + Q ( V1)d where P and Q are constants. Using your answers in (d)(iii), determine values for P and Q. Give appropriate units. P = ............................................................... Q = ............................................................... [2] (f) Wire A has the same length L as the wire between the nails. Theory suggests that 1 P = – and Q = L. L A student repeats the experiment using two shorter wires of equal length. Sketch 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 L to the nearest mm with unit and in the range 74.0–76.0 cm. 1 1(b) Values of raw V1 and V2 to the nearest mV with unit. 1 V2  V1. 1 1(c) Six sets of readings of d, V1 and V2 with correct trend (d increases as average V1 increases and average V2 decreases) and without help from the Supervisor scores 4 marks, five sets scores 3 marks, etc. 4 Range: dmin ⩽ 22.0 cm and dmax ⩾ 65.0 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. ( 2 1 V V )d / m, d2 / m2. 1 Significant figures: All values of ( 2 1 V V )d must be given to the same number of s.f. as (or one more than) the least number of s.f. in d, V1 and V2. 1 Calculation: Correct calculation of ( 2 1 V V )d. 1 Question Answer Marks 1(d)(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 the x and y directions. Axes must be labelled with the quantity that is being plotted. Scale markings are no more than 2 cm (one large square) 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 in both x and y directions. 1 Quality: All points in the table must be plotted (at least 5) on the grid for this mark to be awarded. Trend of points must be negative. It must be possible to draw a straight line that is within  2.5 cm (to scale) on the ( 2 1 V V )d axis of all plotted points. 1 1(d)(ii) Line of best fit: Judge by the 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. Allow one anomalous point 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. Lines must not be kinked or thicker than half a small square. 1 1(d)(iii) Gradient: The hypotenuse of the triangle used must 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. Method of calculation must be correct (not x / y). Gradient sign on answer line matches graph drawn. 1 y-intercept: Correct read-off from a point on the line and 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 d2 = 0, accurate to half a small square. 1 Question Answer Marks 1(e) Value of P = candidate’s gradient and value of Q = candidate’s intercept. The values must not be fractions. 1 Unit for P: m–1, cm–1 or mm–1 and unit for Q: m, cm or mm. 1 1(f) Line labelled W with steeper gradient and smaller intercept. W 1

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2 In this experiment, you will investigate the motion of two connected masses. You have been provided with two masses connected by a string. The larger mass is 100 g and the smaller mass is 10 g. (a) (i) ● Set up the apparatus as shown in Fig. 2.1. boss 10 g mass 100 g mass rod of clamp string stand bench Fig. 2.1 ● Hold the 10 g mass so that the string is horizontal and as straight as possible and the 100 g mass is as close to the rod of the clamp as possible. The string should be resting on the rod of the clamp. When the 10 g mass is released, the 100 g mass will fall downwards. The 10 g mass will fall and move towards the stand. The string will wrap itself several times around the rod of the clamp. You may need to repeat the procedure several times before you see this result. ● Release the 10 g mass. ● The distance fallen by the 100 g mass is A, as shown in Fig. 2.2. A Fig. 2.2 Measure and record A. A = ......................................................... [2] (ii) Estimate the percentage uncertainty in your value of A. Show your working. percentage uncertainty = ......................................................% [1] (b) Fig. 2.3 shows the 10 g mass held so that the angle between the string and the vertical is θ. θ Fig. 2.3 (i) ● Hold the string so that θ is approximately 65°. ● Release the 10 g mass. ● The distance fallen by the 100 g mass is H, as shown in Fig. 2.4. H Fig. 2.4 Measure and record θ and H. θ = ............................................................. ° H = ...............................................................

Mark scheme: 2(a)(i) 1 Evidence of repeat readings. 1 2(a)(ii) Percentage uncertainty in A based on absolute uncertainty ⩾ 3 mm. If several readings have been taken, then the absolute uncertainty can be half the range (but not zero) provided the working is clearly shown. Correct method of calculation to obtain percentage uncertainty. 1 2(b)(i) Value of  to the nearest degree in the range 60°–70°. 1 Value of H with unit. 1 2(b)(ii) Correct calculation of cos2 . 1 2(c) Second value of . 1 Second value of H. 1 Second value of H > first value of H. 1 2(d)(i) Two values of k calculated correctly. The final k values must not be written as fractions. 1 2(d)(ii) Justification for significant figures in k linked to significant figures in H, A and either  or cos  . 1 2(e) Calculation of percentage difference between candidate’s two k values. Comparison of percentage difference with 20% leading to a consistent conclusion. 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  or angle with reason e.g. hand moves during measurement/holding protractor in hand/parallax error/string too thick. C Difficult to judge the horizontal or vertical. D Masses or strings collide/hit stand/string wraps around boss/string slips off rod of clamp/trajectory of motion out of alignment/masses not in the right plane. E Difficult to measure H or A with reason e.g. uncertain where the top measurement is/measured distance not the same as the height the mass falls/mass moves when touched or measured. 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 Method to improve measurement of  e.g. clamp the 10 g mass or clamp protractor/thinner string/put a board behind with marked angle(s)/take a photo and measure angle/project angle onto a screen/use a stop at the correct angle. C Method to determine the vertical or horizontal e.g. use a plumb-line/spirit level/set square with detail. D Method to improve alignment e.g. use longer rod/notched rod/larger diameter on end of rod/place plasticine on the end of the rod/use guide. E Improved method to measure H or A e.g. use a clamped pointer/take a photo with a scale/use large dividers or calipers. 1 mark for each point up to a maximum of 4. 4

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