Cambridge A Level Physics 9702 — 2011 Oct/Nov Paper 3 · Variant 4

1 In this experiment, you will investigate the variation of a potential difference in a resistor network. (a) Set up the circuit of Fig. 1.1. The resistor R should have a resistance R where R = 2.2 kΩ. – + 3 V d.c. R X + V X X component holder Fig. 1.1 (b) Close the switch and record the voltmeter reading V, which should be in the range +0.10 V to +0.90 V. Open the switch. V = ...................................................[1] (c) (i) Change resistor R for one of another value. Close the switch and record the new resistance R and the voltmeter reading V. Open the switch. R = ................................................ kΩ V = ...................................................... (ii) Repeat (c)(i) until you have six sets of readings for R (in kΩ) and V. Include in your For R Examiner’s table of results values for , where R is in kΩ. Use R + 1 Some resistors may give negative values for V. [11] R (d) (i) Plot a graph of V on the y-axis against on the x-axis. [3] R + 1 (ii) Draw the straight line of best fit. [1] (iii) Determine the gradient and y-intercept of this line. gradient = ....................................................... y-intercept = ...................................................... [2] For Examiner’s Use (e) The relationship between V and R is For Examiner’s R Use V = a – b R + 1 where a and b are constants, and R is in kΩ. Using your answers from (d)(iii), determine the values of a and b. Give an appropriate unit for b. a = ....................................................... b = ....................................................... [2] You may not need to use all of the materials provided. For Examiner’s

Mark scheme: 1 (a) Measurement for V in range +0.10 V to +0.90 V, with unit. [1] (c) (ii) Six sets of values for R and V scores 6 marks, five sets scores 5 marks etc. [6] Incorrect trend –1. Major help from supervisor –2, minor help –1. Range: [1] R values must include 0.33 kΩ or less and 4.7 kΩ or more. 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. Consistency of presentation of raw readings: [1] All raw values of V must be given to the same precision and at least 2 d.p. Significant figures: [1] R/(R + 1) must be given to the same as or one more than the s.f. for R. Calculation: [1] R/(R + 1) calculated correctly. (d) (i) Axes: [1] Sensible scales must be used, no awkward scales (e.g. 3:10). Scales must be chosen so that the plotted points must occupy at least half the graph grid in both x and y directions. Scales must be labelled with the quantity which is being plotted. Scale markings must be no more than 3 large squares apart. Plotting of points: [1] All observations in the table must be plotted. Check that the points are correctly plotted. 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. Scatter of points must be less than ± 0.04 V on the V axis from a straight line. (ii) Line of best fit: [1] Judge by balance of all the 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. There must be 5 points left after the anomalous point is disregarded. GCE AS/A LEVEL – October/November 2011 9702 34 (d) (iii) Gradient: [1] The hypotenuse of the triangle used must be at least half the length of the drawn line. Both read-offs must be accurate to half a small square or better in both x and y directions. The method of calculation must be correct. 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 in both x and y directions. Allow ecf of gradient value. Or: Check the read-off of the intercept directly from the graph (e) a = value of gradient, b = –(value of intercept). Do not allow a fraction. [1] Value of b is in range 1.0 V to 2.0 V, with unit V. [1] [Total: 20]

More questions on Practical circuits

2 In this experiment you will investigate the effect of cross-sectional area on the breaking force Use of polythene. (a) You are provided with eight strips of polythene, each with a hole at one end. Four of the strips are marked P and four are marked Q. For one of the strips, measure and record the thickness t of the polythene (measure near the end without the hole). t = ..................................................[1] (b) Each strip has two cuts in it, as shown in Fig. 2.1. paper cuts w hole P polythene adhesive tape Fig. 2.1 For the strips marked P, (i) measure the distance w between the cuts, w = ...........................................mm [2] (ii) estimate the percentage uncertainty in w. percentage uncertainty = ..................................................[1] (c) The cross-sectional area A of the strip between the cuts is shown in Fig. 2.2. For Examiner’s Use w A Fig. 2.2 Calculate A using the relationship A = wt. A = ......................................... mm2 [1] (d) (i) Lay a strip marked P on the bench and hook the newton-meter through the hole. Use a piece of adhesive tape to fix the other end of the strip to the bench, as shown in Fig. 2.3. adhesive tape approximately 2.5 cm Fig. 2.3 (ii) Slowly pull the newton-meter until the strip breaks. (iii) Repeat (d)(i) and (d)(ii) for the other strips marked P. Record the average breaking force F. F = ..................................................[2] (e) Repeat (b)(i), (c) and (d), but this time using the strips marked Q. For Examiner’s Use w = ............................................... mm A = .............................................. mm2 F = ...................................................... [3] (f) (i) It is suggested that the relationship between F and A is F = kA where k is a constant. 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) Value of t in range 0.01 to 0.05 mm, with unit. [1] (b) (i) Value of w in range 5 to 15 mm. Raw reading(s) must be to nearest mm. [1] Evidence of repeated readings of w. [1] (ii) Percentage uncertainty in w based on absolute uncertainty of 1 mm [1] (but if repeated readings have been taken then the absolute uncertainty could be half the range, unless this is zero). Correct method used to find the % uncertainty. (c) Correct calculation of A using candidate’s values from (a) and (b). [1] (d) (iii) At least three measurements of F used. [1] Average calculated correctly, with unit. [1] (e) Second value of w. [1] Second value of F. [1] F increases as w increases. [1] (f) (i) Two values of k calculated correctly. [1] (ii) Sensible comment relating to the calculated values of k, testing against a [1] criterion specified by the candidate.. GCE AS/A LEVEL – October/November 2011 9702 34 (g) (i) Limitations 4 max. (ii) Improvements 4 max. Do not credit A Two readings are not enough Take more readings and plot ‘Few readings’/‘take more (to draw a conclusion) a graph/calculate more k readings and calculate values (and compare) average k’/‘only one reading’ B Difficult to see Video (plus ‘slow motion’ or Just ‘use video camera’ maximum/breaking F/break ‘to view force’ or ‘to view happens suddenly newton-meter’) use maximum-hold newton-meter/ use weights (e.g. sand) to measure F C Difficult to see ends of Use contrasting ‘Difficult to measure w’/use cuts/difficult to measure w background/mark ends of cuts coloured polythene because strip is transparent/ same colour as background D w measurement has low Improved method of precision measuring w e.g. use vernier calliper or use travelling microscope/use larger w E t not constant Measure t between cuts Micrometer squashes polythene F Large (%) uncertainty/error in Improved method of t measuring t e.g. measure several layers or use digital micrometer for better precision G Sellotape detaches from Improved method of fixing to ‘use stronger tape’ bench bench e.g. use clamp or use wider tape or use glue or use stickier tape H t (or w) changes as strip Measure just before or after stretches/as F increases strip breaks Do not allow ‘repeated readings’ Do not allow ‘use a computer to improve the experiment’ [Total: 20]

More questions on Physical quantities