Cambridge A Level Physics 9702 — 2022 May/June Paper 3 · Variant 4

1 In this experiment you will investigate an electrical circuit. (a) You have been provided with the circuit shown in Fig. 1.1. + S 1 C + component holder 2 Fig. 1.1 ● Connect the voltmeter in parallel with component C, as shown in Fig. 1.2. + S 1 C F + 2 V X Fig. 1.2 ● Connect the resistor labelled F in parallel with the component holder, as shown in Fig. 1.2. ● Connect one of the labelled resistors into the component holder as resistor X, as shown in Fig. 1.2. Record the resistance R of resistor X. R = ............................................................... ● Switch on the power supply. ● Move S to position 1. ● Record the voltmeter reading V. V = ......................................................... [1] (b) ● Ensure S is at position 1. ● Move S to position 2 and start the stop‑watch. The voltmeter reading will gradually decrease. ● Stop the stop‑watch when the voltmeter reading passes 0.8 V. ● Record the time t shown by the stop‑watch. t = ............................................................... ● Move S to position 1. [2] (c) Change X and repeat (b) until you have six sets of values of R and t. 1 1 Record your results in a table. Include values of and in your table. R t [9] 1 1(d) (i) Plot a graph of on the y‑axis against on the x‑axis. [3] t R (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 t and R are related by the equation 1 a = + b t R where a and b are constants. Use your answers in (d)(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) Value of V in range 5.00–7.00 V with unit and to the nearest 0.01 V. 1 1(b) Value for t with unit in the range 2.0–20.0 s. 1 Evidence of repeat readings for t. 1 1(c) Six sets of readings of R and t with correct trend (as R increases, t increases) and without help from the Supervisor scores 4 marks, five sets scores 3 marks etc. 4 Range: Rmin ⩽ 22 k and Rmax ⩾ 470 k. 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 / R (k–1). 1 Consistency: Values of t must all be given to the nearest 0.1 s or all to the nearest 0.01 s. 1 Significant figures: All values of 1 / t must be given be to the same number of s.f. as (or one more than) the s.f. in the corresponding value of t. 1 Calculation: Values of 1 / t calculated correctly. 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) for this mark to be awarded. Trend of points must be positive It must be possible to draw a straight line that is within  0.0025 k–1 on the 1 / R 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 substituted into y = mx + c or an equivalent expression, with 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 1 / R = 0, accurate to half a small square. 1 Question Answer Marks 1(e) Value of a = candidate’s gradient and value of b = candidate’s intercept. The values must not be fractions. 1 Units for a and b correct (e.g.  s–1 for a and s–1 for b). 1

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2 In this experiment, you will compare some of the properties of two liquids. (a) You are provided with a block of transparent material with a string loop attached to its rear face, as shown in Fig. 2.1. rear face string loop front face transparent block Fig. 2.1 ● Hook the newton meter through the string loop. ● Record the weight W of the block shown by the newton meter. W = ...................................................... N [1] (b) (i) ● Place the large transparent plate flat on the bench. ● Use the beaker labelled WATER and its pipette to make a pool of water of approximate diameter 5 cm near the centre of the large plate. ● Place the front face of the transparent block on the pool of water. There should be a film of water over the whole of the front face of the block, as shown in Fig. 2.2. ● Hold the large plate down on the bench. ● Hook the newton meter through the string loop and slowly pull up vertically on the block. newton meter string loop large plate block pool of water Fig. 2.2 ● Record the newton meter reading F at the moment the block is detached from the plate. F = ...................................................... N [2] (ii) Estimate the percentage uncertainty in your value of F. Show your working. percentage uncertainty = ......................................................% [1] (iii) Calculate E using E = F – W. E = ...................................................... N [1] (c) ● Use the stand, boss and clamp to position the syringe body above the beaker of water, as shown in Fig. 2.3. stand syringe body boss syringe nozzle pipette clamp bench beaker water Fig. 2.3 ● Cover the nozzle with a finger. ● Use the pipette to fill the syringe with water until the level is above the 10 cm3 mark. ● Uncover the nozzle and start the stop‑watch when the level passes the 10 cm3 mark. ● Stop the stop‑watch when the level passes the 1 cm3 mark. ● Record the stop‑watch reading T. T = ...................................................... s [2] (d) ● Use paper towels to dry the water from the large plate, the block and the syringe body. ● Repeat (b)(i), (b)(iii) and (c) with oil, using the beaker labelled OIL and its pipette. F = ............................................................ N E = ............................................................ N T = ............................................................. s [2]

Mark scheme: 2(a) Value for W to at least nearest 0.1 N. 1 2(b)(i) Raw values of F to at least nearest 0.1 N. Repeated readings, if present, have the same precision. 1 Repeated readings for F. 1 2(b)(ii) Percentage uncertainty in F based on an absolute uncertainty of 0.20–0.50 N. If several readings have been taken, then the absolute uncertainty can be half the range (but not zero) provided working is clearly shown. Correct method of calculation to obtain percentage uncertainty. 1 2(b)(iii) Correct calculation of E. 1 2(c) Value for T in range 2.0–30.0 s. 1 Repeated readings for T. 1 2(d) Second values of F and T. 1 Second F > first F. 1 2(e)(i) Two values of k calculated correctly. The final k values must not be written as fractions. 1 2(e)(ii) Justification based on significant figures in E (or F and W) and T. 1 2(f) Calculation of percentage difference between candidate’s two k values. Comparison of percentage difference with 40% leading to a consistent conclusion. 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 Difficult to measure W with reason e.g. newton meter scale not precise enough/newton meter doesn’t move off zero. C Block tends to slide towards edge of plate/newton meter not vertical. D Difficult to measure F with reason e.g. block detaches suddenly/difficult to judge or predict when block will leave the surface/reading is only at the value for a short time. E Difficulty with F or W or E since value is very small so large uncertainty/large percentage uncertainty. F Difficult to measure T with reason e.g. difficult to judge/determine moment when water level passes mark on syringe. 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 Measure W using an electronic scale. C Workable method of ensuring the newton meter operates vertically e.g. attach string to newton meter and have string guide fixed above centre of plate/use of plumb-line to help judgement of vertical. D Video/film/record newton meter or use data logger/force sensor and find F/maximum reading/maximum force or use newton meter with maximum hold indication. E Use a block that is larger/heavier/denser/wider. F Video/film/record syringe with timer in view. 1 mark for each point up to a maximum of 4. 4

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