Cambridge A Level Physics 9702 — 2011 May/June Paper 3 · Variant 1

1 In this experiment you will investigate how the characteristics of a circuit vary with its resistance. (a) Connect the circuit of Fig. 1.1. You should expect to spend at least 15 minutes setting up your circuit. V A B D C Fig. 1.1 (b) (i) Close the switch. (ii) Adjust the variable resistor until the current reading is at a maximum. (iii) Measure and record the ammeter reading Ι and the voltmeter reading V. Ι = ..................................................... V = ..................................................... [2] (c) Adjust the variable resistor and repeat (b)(iii) until you have six sets of values of Ι For and V. Include values of and in your table. Examiner’s 1–Ι 1–V Use Open the switch when you have taken all your readings. [10] (d) (i) Plot a graph of on the y-axis against on the x-axis. [3] 1–Ι 1–V (ii) Draw the straight line of best fit. [1] (iii) Determine the gradient and the y-intercept of this line. gradient = ..................................................... y-intercept = ..................................................... [2] For Examiner’s Use (e) It is suggested that the quantities Ι and V are related by the equation For Examiner’s 3R Use = ––– + k 1–Ι V where R and k are constants. Use your answer in (d)(iii) to determine the value of R. Give appropriate units. R = ................................................ [2] You may not need to use all of the materials provided. For Examiner’s Use

Mark scheme: 1 (b) (iii) Value of I non-zero value and 10 mA with unit. [1] Value of V 0.5 V 1.5 V with unit. [1] (c) Six sets of readings of I and V scores 5 marks, five sets scores 4 marks etc. [5] Incorrect trend then –1. Minor help from supervisor –1; major help –2. Range: Range of I at least 0.3 mA. [1] Column headings: [1] Each column heading must contain a quantity and a unit where appropriate. There must be some distinguishing mark between the quantity and the unit e.g. V / V. Consistency of presentation of raw readings: [1] All values of I must be given to the same number of decimal places. All values of V must be given to the same number of decimal places. Significant figures: [1] Significant figures for 1/V the same as, or one more than, that for V. Calculation: Check the values of 1/V and 1/I. [1] (d) (i) Axes: [1] Sensible scales must be used. Awkward scales (e.g. 3:10) are not allowed. Scales must be chosen so that the plotted points on the grid occupy at least half the graph grid in both x and y directions. Scales must be labelled with the quantity that is being plotted. Ignore units. Scale markings should not be greater than three large squares apart. Plotting of points: [1] All the observations in the table must be plotted. Check the points are plotted correctly. Work to an accuracy of half a small square. Do not accept blobs (points with diameter greater than half a small square). Quality: [1] All points in the table must be plotted (at least 5) for this mark to be scored. Judge by the scatter of all points about a straight line. All points must be within 0.01 V–1 on the 1/V axis from a straight line. (ii) Line of best fit: [1] Judge by the balance of all the points (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. (iii) Gradient: [1] The hypotenuse of the triangle must be at least half the length of the drawn line. Read- offs must be accurate to half a small square. Intercept: [1] Either: Check correct read-off from a point on the line, and substitution into y = mx + c. Read- off must be accurate to half a small square. Allow ecf of gradient value. Or: Check the read-off of the intercept directly from the graph. GCE A LEVEL – May/June 2011 9702 31 (e) Correct method to find R. [1] Answer in range 40 – 60 Ω with unit. [1] [Total: 20]

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2 In this experiment you will investigate how the motion of a metre rule balanced on a cylinder depends on the diameter of the cylinder. (a) Measure and record the thickness t of the metre rule. t = ................................................. [1] (b) (i) Measure and record the diameter d of cylinder A. d = ................................................. [1] (ii) Calculate w, where w = d – t. w = ................................................. [1] (c) (i) Use modelling clay to secure cylinder A to the bench and balance the metre rule on the cylinder, as shown in Fig. 2.1. metre rule modelling cylinder A clay bench Fig. 2.1 (ii) Move one end of the rule downwards. For Release the rule and watch the movement. Examiner’s The end of the rule will move upwards and then downwards again, completing a Use swing as shown in Fig. 2.2. The time taken for each complete swing is T. one complete swing Fig. 2.2 By timing several of these complete swings, determine an accurate value for T. T = ................................................. [2] (d) Estimate the percentage uncertainty in your value of T. percentage uncertainty = ................................................. [1] (e) Repeat (b) and (c) for cylinder B. For Examiner’s Use d = ..................................................... w = ..................................................... T = ..................................................... [4] (f) It is suggested that the quantities T and w are related by the equation T 2 = k–– w where k is a constant. (i) Using your data, calculate two values of k. first value of k = ..................................................... second value of k = ..................................................... [1] (ii) Explain whether your results support the suggested relationship. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. ..............................................................................................................................[1]

Mark scheme: 2 (a) Measurement of t in the range 0.20 cm – 1.00 cm to 0.1 mm or 0.01 mm with unit. [1] (b) (i) Measurement of d in the range 3 cm – 9 cm with unit. [1] (ii) Correct calculation of w. [1] (c) (ii) Value of T in the range 3 s – 5 s. [1] Evidence of repeat readings. [1] (d) Absolute uncertainty in T in range 0.1 s – 0.6 s. [1] If repeated readings have been taken, then the uncertainty can be half the range. Correct method of calculation of percentage uncertainty. (e) Second value of d in the range 14 cm – 31 cm . [1] Correct calculation of second value of w. [1] Second value of T. [1] Second value of T < first value of T. [1] (f) (i) Correct calculation of two values of k. [1] (ii) Sensible comment relating to the calculated values of k, testing against a specified criterion. [1] GCE A LEVEL – May/June 2011 9702 31 (g) (i) Limitations 4 max (ii) Improvements 4 max Do not credit: A Two readings are not Take more readings and plot Few readings enough a graph/ calculate more k Take more readings and (to draw a conclusion) values (and compare) calculate average k Allow ‘repeat readings and plot a graph’ Only one reading B Rule hits bench Method of preventing rule hitting bench Ignore amplitude e.g. project end of cylinder over bench changes/difficult to start or elevate apparatus at the same amplitude each time C rule used for wider diameter/ Method to improve measurement of Use larger Vernier couldn’t use calipers larger diameter e.g. use set squares calipers held against ruler/wrap string or paper around and measure circumference/use calipers and hold against ruler/travelling microscope D Difficult to judge when 1.Use video (+ playback) + timer/use Difficult to measure the oscillation is complete clock on video / use position or motion time/human error/ sensor placed above/below rule (not references to reaction above centre) / use of light gate with times detailed method. 2.Use (fiducial) marker/pointer at centre (of oscillation) E Oscillations die away quickly/too few oscillations/ damped F Use same surface/material (for cylinders) Ignore ‘parallax problems’, ‘use assistant’ or references to draughts, fans, air conditioning. [Total: 20]

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