Cambridge A Level Physics 9702 — 2008 Oct/Nov Paper 5 · Variant 1

READ THESE INSTRUCTIONS FIRST Write your Centre number, candidate number and name on all the 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 all questions. You may lose marks if you do not show your working or if you do not use appropriate units. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 2 Total This document consists of 8 printed pages. SPA (KN) T50107/4 © UCLES 2008 [Turn over UNIVERSITY OF CAMBRIDGE INTERNATIONAL EXAMINATIONS General Certificate of Education Advanced Level * 1 2 2 7 2 3 0 3 4 7 * PHYSICS 9702/05 Paper 5 Planning, Analysis and Evaluation October/November 2008 1 hour 15 minutes Candidates answer on the Question Paper. No Additional Materials are required.

2 9702/05/O/N/08 © UCLES 2008 For Examiner’s Use 1 A student wishes to investigate how the resistance R of a light-dependent resistor varies with the distance d from an intense light source. It is believed that the relationship between R and d is R = kd n where k and n are constants. Design a laboratory experiment to test the above relationship. The light-dependent resistor has a resistance of 100 Ω when it is in bright light and a resistance of 500 kΩ when no light falls on it. You should draw a diagram showing the arrangement of your equipment. In your account you should pay particular attention to (a) the procedure to be followed, (b) the measurements that would be taken, (c) the control of variables, (d) how the data would be analysed, (e) any safety precautions that you would take. [15]

3 9702/05/O/N/08 © UCLES 2008 [Turn over For Examiner’s Use Diagram … … … … … … … … … … … … … … …

4 9702/05/O/N/08 © UCLES 2008 For Examiner’s Use … … … … … … … … … … … … … … … … … … … … … … … … … … …

5 9702/05/O/N/08 © UCLES 2008 [Turn over For Examiner’s Use 2 An experiment was carried out to investigate how the diameter d of the path of a beam of electrons varied with the accelerating voltage V when a magnetic field of flux density B was applied at right angles to the electron beam. The equipment was set up as shown in Fig. 2.1. V + – d electron gun Fig. 2.1 The diameter d was recorded for different voltages V.

6 9702/05/O/N/08 © UCLES 2008 For Examiner’s Use Values of V and d are given in Fig. 2.2. V / V d / 10–2 m d 2 / 10–4 m2 500 2.1 0.1 1000 2.8 0.1 1500 3.4 0.1 2000 3.9 0.1 2500 4.3 0.1 3000 4.7 0.1 Fig. 2.2 It is suggested that V and d are related by the formula e –– m = 8V –––– B 2d 2 where e is the charge on the electron and m is the electron mass. (a) A graph of d 2 on the y-axis against V on the x-axis is to be plotted. Write down an expression for the gradient in terms of e, m and B. … [1] (b) Calculate and record values of (d 2 / 10–4 m2) in Fig. 2.2. Include in the table the absolute errors in d 2. [3] (c) (i) Plot a graph of d 2 on the y-axis against V on the x-axis. Include error bars for d 2. [2] (ii) Draw the best-fit straight line and a worst acceptable straight line on your graph. Both lines should be clearly labelled. [2] (iii) Determine the gradient of the best-fit line. Include the error in your answer. gradient = … [2]

7 9702/05/O/N/08 © UCLES 2008 [Turn over For Examiner’s Use 20 22 24 18 16 14 12 10 8 6 4 2 0 500 1000 1500 2000 2500 V / V d 2 / 10–4 m2 3000

8 9702/05/O/N/08 © UCLES 2008 For Examiner’s Use (d) The magnetic flux density B of the magnetic field is 7.9 × 10–3 T. Using the answer to (c)(iii), determine the value of e –– m . Include the error in your value and an appropriate unit. e –– m = … [3] (e) The experiment is repeated with a different magnetic flux density. When V is 500 V, the measured value of d is (3.8 ± 0.1) × 10–2 m. Using your answer to (d), determine a value for the new magnetic flux density, B. Include the error in your value. B = … T [2] 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 October/November 2008 question paper 9702 PHYSICS 9702/05 Paper 5 (Planning, Analysis and Evaluation), maximum raw mark 30 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 October/November 2007 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 – October/November 2008 9702 05 © UCLES 2008 Question 1 Planning (15 marks) Defining the problem (3 marks) P1 d is the independent variable or vary d (allow in table if numbers given) [1] P2 R is the dependent variable or measure R as d varied (allow in table) [1] P3 Keep output of light source constant (allow constant current / e.m.f. / voltage / power) [1] Methods of data collection (5 marks) M1 Diagram showing an LDR in a circuit and an independent lamp. [1] M2 Diagram showing ruler measuring appropriate distance or d labelled correctly. [1] M3 Correct circuit diagram for LDR using conventional symbols; allow labelled diagram [1] Ammeter and voltmeter with power supply, or potential divider methods ohmmeter without power supply, or bridge methods. M4 Method of determining R. [1] Ohmmeter. R = V/I justified. Potential divider equation Description of balancing bridge with correct equation. M5 Perform experiment in a dark room/tube [1] Method of analysis (2 marks) A1 Plot a graph of log R against log d [1] A2 Relationship is correct if log R against log d graph is a straight line [1] Safety considerations (1 mark) S1 Do not look directly at bright light source / do not touch hot light source. [1] Allow safety glasses with reference to light source. Additional detail (4 marks) D1/2/3/4 Relevant points might include [4] Detail on measuring the distance Keep orientation of LDR with respect to the light source constant Reasoned method for keeping light and LDR in correct orientation. (E.g. use of set square, fix to rule, optical bench or equivalent) Determination of a typical current Range of ammeter / ohmmeter Control (or monitoring) of an additional variable e.g. temperature Reason for performing experiment in a dark room related to the LDR Method for checking the output of the light source is constant. Identifies gradient = n and/or y-intercept = log k for log R against log d graph Do not allow parallax when reading ruler, or reflectors. [Total: 15]

Page 3 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9702 05 © UCLES 2008 Question 2 Analysis, conclusions and evaluation (15 marks) Part Mark Expected Answer Additional Guidance (a) A1 2 8 eB m Allow 2 8 B gradient m e = (b) T1 4.4 or 4.41 7.8 or 7.84 12 or 11.6 (or 11.56) 15 or 15.2 (or 15.21) 18 or 18.5 (or 18.49) 22 or 22.1 (or 22.09) Ignore significant figures T2 All values given to two or three significant figures. Must be to two or three significant figures. A mixture of 2s.f. and 3s.f. is allowed. E1 ± 0.4 (allow ± 0.5), ± 0.6, ± 0.7, ± 0.8, ± 0.9, ± 0.9 or ± 1.0 Allow more than one significant figure. (c) (i) G1 Six points plotted correctly. Must be within half a small square. Use transparency. E.c.f. allowed from table. E2 Error bars in d 2 plotted correctly. Check first and last point. Must be accurate within half a small square. (c) (ii) G2 Line of best fit. If points are plotted correctly then lower end of line should pass between (150, 2) and (200, 2) and upper end of line should pass between (3200, 24) and (3250, 23.7). Allow e.c.f. from points plotted incorrectly – examiner judgement. G3 Worst acceptable straight line. Steepest or shallowest possible line that passes through all the error bars. Line should be clearly labelled or dashed. Should pass from top of top error bar to bottom of bottom error bar or bottom of top error bar to top of bottom error bar. Mark scored only if error bars are plotted. (c) (iii) C1 Gradient of best fit line. The triangle used should be greater than half the length of the drawn line. Check the read offs. Work to half a small square. Do not penalise POT. If points and BFL correct then gradient should be in numerical range (7.00 – 7.35) (× 10–7). E3 Error in gradient Method of determining absolute error. Difference in worst gradient and gradient. (d) C2 e/m = 8/(gradient × B2) = 1.28 × 105/gradient = 1.8 × 1011 Gradient must be used. Allow e.c.f. from (c) (iii) but penalise POT. If gradient within range given, then e/m in range (1.74 – 1.83) × 1011. E4 Method of determining error in e/m. Uses worst gradient and finds difference. Allow fractional error methods. Do not check calculation. C3 Unit of e/m: C kg–1. Accept V m–2 T–2.

Page 4 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9702 05 © UCLES 2008 (e) C4 3.80 – 4.00 × 10-3 [If POT in (d) allow 0.38 – 0.40] Check method. 2 2 ) 10 (3.8 500 8 − × × × = m e B Answer must be in range given. E5 Method for determining largest error in correct value of B. This mark can only be scored if B is in range. Expect to see similar calculation to above with largest e/m x (3.9 × 10–2)2 or smallest e/m x (3.7 × 10–2)2. Allow fractional error methods. [Total: 15] Uncertainties in Question 2 (c) (iii) Gradient [E3] 1. Uncertainty = gradient of line of best fit – gradient of worst acceptable line 2. Uncertainty = ½ (steepest worst line gradient – shallowest worst line gradient) (d) e/m [E4] 1. Uncertainty = e/m from gradient – e/m from worst acceptable line 2. gradient gradient m e m e ∆ ∆ = (e) B [E5] 1. Substitution method to find worst acceptable B using either largest e/m × (3.9 × 10–2)2 or smallest e/m × (3.7 × 10–2)2. 2.       + =       + = d d d d B B m e m e m e m e ∆ 2 ∆ 2∆ ∆ 2 1 ∆

Page 5 Mark Scheme Syllabus Paper GCE A/AS LEVEL – October/November 2008 9702 05 © UCLES 2008 Summary of shorthand notation which may be used in annotating scripts: XEX Wrong experiment SFP Significant figure penalty ECF Error carried forward AE Arithmetical error POT Power of ten error NV Not valid NR Not relevant NBL Not best line NWL Not worst line FO False origin NE Not enough NGE Not good enough BOD Benefit of the doubt NA Not allowed SV Supervisor's value SR Supervisor’s report OOR Candidate's value is out of range CON Contradictory physics not to be credited
∆ Used to show that the size of a triangle is appropriate
M3 Used to show the type of mark awarded for a particular piece of work
C Used to show that the raw readings are consistent
SF Used to show calculated quantities have been given to an appropriate number of significant figures ^ Piece of work missing (one mark penalty) ^^ Several pieces of work missing (more than one mark penalty) ↔ Scale can be doubled in the x-direction b Scale can be doubled in the y-direction