Cambridge A Level Physics 9702 — 2008 May/June Paper 3 · Variant 1

This document consists of 9 printed pages and 3 blank pages. SP SHW 00011 3/07 T50155/3 © UCLES 2008 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Subsidiary Level and Advanced Level READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all work you hand in. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use staples, paper clips, highlighters, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer both questions. You will be allowed to work with the apparatus for a maximum of one hour for each question. You are expected to record all your observations as soon as these observations are made, and to plan the presentation of the records so that it is not necessary to make a fair copy of them. The working of the answers is to be handed in. Additional answer paper and graph paper should be submitted only if it becomes necessary to do so. You are reminded of the need for good English and clear presentation in your answers. At the end of the examination, fasten all your work securely together. All questions in this paper carry equal marks. * 6 1 4 7 6 0 7 2 2 1 * PHYSICS 9702/31 Paper 31 Advanced Practical Skills 1 May/June 2008 2 hours Candidates answer on the Question Paper. Additional Materials: As listed in the Confidential Instructions. For Examiner’s Use 1 2 Total

3 9702/31/M/J/08 [Turn over © UCLES 2008 For Examiner’s Use You may not need to use all of the materials provided. 1 In this experiment you will investigate how the angles of the strings in a pulley system are affected by the mass suspended from the mid-point of the string. From these results you will determine the mass. (a) Set up the apparatus as shown in Fig. 1.1. Clamp the pulleys so that they are 50 cm above the bench and 30 cm from each other. Take the ends of the string and feed them through each pulley. Hang a 0.200 kg mass from each end of the string. Suspend the object holder from the middle loop in the string. 30 cm 50 cm 200 g mass 200 g mass object holder pulley pulley Fig. 1.1 (b) Place one of the eleven identical objects in the object holder and measure the angle θ between the strings as shown in Fig. 1.2. tension T tension TT
Fig. 1.2 θ = …

4 9702/31/M/J/08 © UCLES 2008 For Examiner’s Use (c) Repeat (b), changing the number of objects placed in the object holder. Repeat this procedure until you have six sets of readings for the number n of objects and angle θ. Include in your table of results values for θ 2 and cos ( θ 2). (d) Plot a graph of cos( θ 2) on the y-axis against the number n of objects on the x-axis and draw the line of best fit. (e) Determine the gradient and y-intercept of this line. gradient = … y-intercept = …

5 9702/31/M/J/08 [Turn over © UCLES 2008 For Examiner’s Use

6 9702/31/M/J/08 © UCLES 2008 For Examiner’s Use (f) Determine the value of the tension T in one of the strings shown in Fig. 1.2. The value of g is 9.81 N kg–1. T = … N (g) It is suggested that the relationship between cos( θ 2) and n is cos( θ 2) = mgn 2T + k where m is the mass of one object and k is a constant. Use your answers from (e) and (f) to determine a value for m. m = …

7 9702/31/M/J/08 [Turn over © UCLES 2008 For Examiner’s Use You may not need to use all of the materials provided. 2 In this question you will investigate how the light detected by a light-dependent resistor (LDR) depends on the thickness of an absorber. (a) (i) Connect the circuit shown in Fig. 2.1. The light-emitting diode (LED) should be connected the right way round so that light is emitted. V LDR LED + – Fig. 2.1 (ii) Use the black paper and the Sellotape to make a cylinder of length 4 cm. The cylinder should fit neatly over the LDR. (iii) Cut the cylinder in half so that you have two cylinders of length 2 cm. (iv) Tape one cylinder over the LDR and the other cylinder over the LED as shown in Fig. 2.2. 2 cm 2 cm Sellotape Sellotape LDR LED Fig. 2.2 (b) Place the cylinders together, as shown in Fig. 2.3. Record the voltmeter reading V0. Fig. 2.3 V0 = …

8 9702/31/M/J/08 © UCLES 2008 For Examiner’s Use (c) Fold the sheet of tracing paper in half four times so that you have 16 layers. (i) Measure the thickness of these 16 layers. thickness of 16 layers = … (ii) Estimate the percentage uncertainty in this measurement. Show your working. percentage uncertainty = … (iii) Determine the thickness t of one layer of tracing paper. t = … (iv) Justify the number of significant figures you have given for t. … … … …

9 9702/31/M/J/08 [Turn over © UCLES 2008 For Examiner’s Use (d) (i) Place four layers of tracing paper between the LED and the LDR as shown in Fig. 2.4. Record the voltmeter reading V. LDR LED Fig. 2.4 V = … (ii) Repeat (i) using eight layers of tracing paper. V = … (e) Explain whether your results support the idea that V – V0 is proportional to the number of layers n of tracing paper. … … … … …

10 9702/31/M/J/08 © UCLES 2008 For Examiner’s Use (f) (i) State four sources of error or limitations of the procedure for this experiment. 1. … … 2. … … 3. … … 4. … … (ii) Suggest four improvements that could be made to the experiment. You may suggest the use of other apparatus or different procedures. 1. … … 2. … … 3. … … 4. … …

12 9702/31/M/J/08 BLANK PAGE Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (UCLES) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. University of Cambridge International Examinations is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.

UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS GCE Advanced Subsidiary Level and GCE Advanced Level MARK SCHEME for the May/June 2008 question paper 9702 PHYSICS 9702/31 Paper 31 (Advanced Practical Skills 1), maximum raw mark 40 This mark scheme is published as an aid to teachers and candidates, to indicate the requirements of the examination. It shows the basis on which Examiners were instructed to award marks. It does not indicate the details of the discussions that took place at an Examiners’ meeting before marking began. All Examiners are instructed that alternative correct answers and unexpected approaches in candidates’ scripts must be given marks that fairly reflect the relevant knowledge and skills demonstrated. Mark schemes must be read in conjunction with the question papers and the report on the examination. • CIE will not enter into discussions or correspondence in connection with these mark schemes. CIE is publishing the mark schemes for the May/June 2008 question papers for most IGCSE, GCE Advanced Level and Advanced Subsidiary Level syllabuses and some Ordinary Level syllabuses.

Page 2 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9702 31 © UCLES 2008 1 Manipulation, measurement and observation Successful collection of data (b) Apparatus setup without help from supervisor. [1] (b) Value of 90° ≤ θ ≤ 180°. [1] (c) Six sets of values for θ and n scores 4 marks, five sets scores 3 marks, etc. [4] Wrong trend –1 (θ increases, n increases; On graph: negative slope). (c) Repeat readings. [1] Range and distribution of values (c) Need 0/1/2 and 10/11. [1] Presentation of data and observations Table: layout (c) Column headings (n (no unit), θ / °, θ/2 / °, cos(θ/2) (no unit), cos(θ/2(˚)) ). [1] Each column heading must contain a quantity and a unit where appropriate. Ignore units in the body of the table. There must be some distinguishing mark between the quantity and the unit (i.e. solidus is expected, but accept, for example, θ (°)). Allow θ in degrees/θ in °. Table: raw data (c) Consistency of presentation of raw readings of θ. If no θ column –1. [1] Expect integer values. Allow to the nearest degree (e.g. 23, 23.0, 23.5). All values of θ must be given to the same number of decimal places. Table: calculated quantities (c) Significant figures. If no θ column –1. [1] Apply to cos(θ/2). If θ is given to 2 sf, then accept cos(θ/2) to 2 or 3 sf. If θ is given to 3 sf, then accept cos(θ/2) to 3 or 4 sf. If θ is given to 4 sf, then accept cos(θ/2) to 4 or 5 sf. (c) Values of cos(θ/2) correct. Use average if present. [1] Underline and check a value. If incorrect, write in the correct value. Ignore small rounding errors. Graph: layout (Graph) Axes. Allow inverted axis. Wrong axis –1. [1] Sensible scales must be used. Awkward scales (e.g. 3:10) are not allowed. Scales must be chosen so that the plotted points must occupy at least half the graph grid in both x (4 ) and y (6 ) directions. Scales must be labelled with the quantity that is being plotted. Ignore units.

Page 3 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9702 31 © UCLES 2008 Graph: plotting of points (Graph) All observations must be plotted. [1] Work to an accuracy of plot ≤ 0.5 small square. If any plot diameter ≥ 0.5 small square –1. Graph: trend line (Graph) Line of best fit. Allow line from 5 trend plots. [1] Judge by scatter of points about the candidate's line. There must be a fair scatter of points either side of the line. If line thicker than 0.5 small square –1. Quality of data (Graph) Judge by scatter of points (± 0.4 object) about the examiner’s line. [1] All plots from table are needed (minimum 6) for this mark to be scored. If –ve trend or wrong axis on graph, no mark. Analysis, conclusions and evaluation Interpretation of graph (e) Gradient [1] The hypotenuse of the ∆ must be equal to or greater than half the length of the drawn line. Read-offs must be accurate to half a small square. Check for ∆y/∆x (i.e. do not allow ∆x/∆y). (e) y-intercept from graph or substitute correct read-offs into y = mx + c (Close to 0). [1] Check false origin. Correct substitution needed and no algebraic error (e.g. y/mc = c). Allow ecf from gradient. Drawing conclusions (f) Value for T. Allow 1 SF. Valid values: 2, 2.0, 1.96, 1.962 N. [1] (g) Value for m. Use of gradient = mg/2T. Not substitution method. [1] Unit consistent with value. In range 0.010 – 0.050 kg (10 – 50 g). 2 or 3 SF. If no unit is given then this mark cannot be scored. [Total: 20]

Page 4 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9702 31 © UCLES 2008 2 Manipulation, measurement and observation Successful collection of data (b) Set up apparatus to get V0. Minor help –1, e.g. incorrect connections of LED. Major help –2, e.g. set up circuit. [2] (b) Voltmeter reading, V0. Sensible value with unit. V0 ≤ 4.00 V ± 0.01 V. 2/3 d.p. [1] (c) (i) Evidence of repeats. Consistent unit. Reading ± 0.01 mm or 0.001 mm. Range 0.5 mm ≤ 16t ≤ 5 mm. [1] (d) (i) Measurement of voltage V. If (d)(i) and/or (d)(ii) negative –1. [1] (d) (ii) Measurement of voltage V. [1] Quality of data (d) (ii) V0 < V(d)(i) < V(d)(ii) [1] Presentation of data and observations Display of calculation and reasoning (c) (iii) Calculation of one thickness t. 16t / 16. Check calculation ((c)(i)/16). Allow ecf (c)(i). [1] (c) (iv) Justify the number of significant figures in t, related to no. of SF in 16t / raw data. [1] (Same number of significant figures in 16t or one more.) Decimal place arguments scores zero. (e) Calculation to check proportionality. Evidence for (V-V0 ) required. Calculate correct ratio (V-V0)/n in both cases. If n = 16, -1. [1] Analysis, conclusions and evaluation Drawing conclusions (e) Conclusion. [1] Sensible comments relating to calculations and suggested relation. Incorrect ideas score zero. Accept reference back to (c)(ii). Estimating uncertainties (c) (ii) Percentage uncertainty in 16t. Consistent units. ∆16t = ± 0.01 mm or 0.001 mm. [1] If repeated readings have been done then the uncertainty could be half the range. Correct ratio idea required (0.01 or 0.001/16t x 100 %). Ecf from (c)(i).

Page 5 Mark Scheme Syllabus Paper GCE A/AS LEVEL – May/June 2008 9702 31 © UCLES 2008 Identifying limitations and suggesting improvements (f) (i) & (ii) Identify limitations and improvements by underlining relevant point and annotating the tick using the following letters in the grid. Problem (P) Solution (S) A Two readings not enough (to draw a conclusion). Take many readings AND plot a graph/find many values of k. B Alignment of cylinders/ alignment of LED/LDR. Guide used; ruler/line on desk./ Adjust LED/LDR to get max voltage/method of fixing LED/LDR in cylinder. C Stray light coming in/not light tight/cylinders not sealed so let light enter tube/external light hits LDR. Dark room/black cloth over head/lights off and blinds down/black box/black tape. D Difficult to hold all together/voltage meter fluctuates. Method of fixing; clamp/plasticine/tape. E Separation between LED and LDR changes (as paper added). Pre-slots in tube. Max 4 Max 4 X – Other valid limitation or improvement. Do not allow ‘varying thickness of paper, zero error on micrometer’. Do not allow ‘repeated readings, parallax error’. Do not allow ‘use a computer to improve the experiment’. Ignore separation of layer affects light getting through and squashing of paper for micrometer reading. [Total: 20]