Cambridge A Level Physics 9702 — 2016 Oct/Nov Paper 5 · Variant 2

This document consists of 8 printed pages. DC (NF/JG) 117177/2 © UCLES 2016 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level * 1 9 9 6 3 7 0 8 3 2 * PHYSICS 9702/52 Paper 5 Planning, Analysis and Evaluation October/November 2016 1 hour 15 minutes Candidates answer on the Question Paper. No Additional Materials are required. 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 an HB pencil for any diagrams or graphs. Do not use staples, paper clips, glue or correction fluid. DO NOT WRITE IN ANY BARCODES. Answer all questions. Electronic calculators may be used. 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.

2 9702/52/O/N/16 © UCLES 2016 1 A student uses a Hall probe to investigate the magnetic flux density due to a U-shaped electromagnet, as shown in Fig. 1.1. p P iron core coil Fig. 1.1 Point P is equidistant from the poles of the electromagnet and distance p is the vertical distance between P and the top of the electromagnet. The magnetic flux density is B at point P. It is suggested that the relationship between B and p is B = kNIe−αp where N is the number of turns on the coil, I is the current in the coil and α and k are constants. Design a laboratory experiment using a Hall probe to test the relationship between B and p. Explain how your results could be used to determine values for α and k. You should draw a diagram, on page 3, showing the arrangement of your equipment. In your account you should pay particular attention to • the procedure to be followed, • the measurements to be taken, • the control of variables, • the analysis of the data, • any safety precautions to be taken. [15]

3 9702/52/O/N/16 © UCLES 2016 [Turn over Diagram … … … … … … … … … … … … … …

4 9702/52/O/N/16 © UCLES 2016 … … … … … … … … … … … … … … … … … … … … … … … … … … … [Total: 15]

5 9702/52/O/N/16 © UCLES 2016 [Turn over 2 A student is investigating the characteristics of different light-emitting diodes (LEDs). Each LED needs a minimum potential difference across it to emit light. The circuit is set up as shown in Fig. 2.1. V Fig. 2.1 The potentiometer is adjusted until the LED just emits light. The potential difference V across the LED is measured. The experiment is repeated for LEDs that emit light of different wavelength λ. It is suggested that V and λ are related by the equation V = pλq where p and q are constants. (a) A graph is plotted of lg V on the y-axis against lg λ on the x-axis. Determine expressions for the gradient and y-intercept. gradient = … y-intercept = … [1]

6 9702/52/O/N/16 © UCLES 2016 (b) Values of λ and V are given in Fig. 2.2. λ / 10−9 m V / V lg (λ / 10−9 m) lg (V / V) 630 1.9 ± 0.1 620 2.0 ± 0.1 590 2.3 ± 0.1 520 3.1 ± 0.1 490 3.7 ± 0.1 470 4.1 ± 0.1 Fig. 2.2 Calculate and record values of lg (λ / 10−9 m) and lg (V / V) in Fig. 2.2. Include the absolute uncertainties in lg (V / V). [3] (c) (i) Plot a graph of lg (V / V) against lg (λ / 10−9 m). Include error bars for lg (V / V). [2] (ii) Draw the straight line of best fit and a worst acceptable straight line on your graph. Both lines should be clearly labelled. [2] (iii) Determine the gradient of the line of best fit. Include the absolute uncertainty in your answer. gradient = … [2]

7 9702/52/O/N/16 © UCLES 2016 [Turn over                    / ² P  lg (9/ 9 h lg (

8 9702/52/O/N/16 © UCLES 2016 (iv) Determine the y-intercept of the line of best fit. Include the absolute uncertainty in your answer. y-intercept = … [2] (d) Using your answers to (a), (c)(iii) and (c)(iv), determine the values of p and q. You need not be concerned with units. p = … q = … [2] (e) A similar experiment is carried out with a diode emitting infra-red radiation of wavelength 950 nm. Determine the minimum potential difference V needed to emit this radiation. V = … V [1] [Total: 15] To avoid the issue of disclosure of answer-related information to candidates, all copyright acknowledgements are reproduced online in the Cambridge International Examinations Copyright Acknowledgements Booklet. This is produced for each series of examinations and is freely available to download at www.cie.org.uk after the live examination series.

® IGCSE is the registered trademark of Cambridge International Examinations. This document consists of 5 printed pages. © UCLES 2016 [Turn over Cambridge International Examinations Cambridge International Advanced Subsidiary and Advanced Level PHYSICS 9702/52 Paper 5 Planning, Analysis and Evaluation October/November 2016 MARK SCHEME Maximum Mark: 30 Published 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, which would have considered the acceptability of alternative answers. Mark schemes should be read in conjunction with the question paper and the Principal Examiner Report for Teachers. Cambridge will not enter into discussions about these mark schemes. Cambridge is publishing the mark schemes for the October/November 2016 series for most Cambridge IGCSE®, Cambridge International A and AS Level components and some Cambridge O Level components.

Page 2 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9702 52 © UCLES 2016 Question Answer Marks 1 Defining the problem p is the independent variable and B is the dependent variable, or vary p and measure B. 1 Keep the current/I (in the electromagnet) constant. 1 Methods of data collection Labelled diagram showing Hall probe correctly positioned (along p) and ruler correctly positioned and either Hall probe or rule supported. 1 Correct circuit diagram to include d.c. power supply in series with coil and ammeter. Must be a workable circuit diagram to measure current through the coil. 1 Measure p with ruler. 1 Method to determine an accurate value of p. Examples include: Height of P above bench – height of electromagnet Height of P measured from ruler across the top of the electromagnet 1 Method of analysis Plot a graph of ln B against p. 1 α = – gradient 1 I N k y intercept e − = 1

Page 3 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9702 52 © UCLES 2016 Question Answer Marks Additional detail including safety considerations 6 1. Keep the number of turns/N constant. 2. Use large number of turns/current (to increase B). 3. Avoid overheating the coil/do not touch hot coil. 4. Use of variable resistor to keep ammeter reading constant. 5. Method to ensure that Hall probe is equidistant from the poles, e.g. determine centre of electromagnet and use of plumb line/ruler and spirit level/set square. 6. Adjust Hall probe until maximum reading obtained/perpendicular to field. 7. Repeat each experiment for the same value of p and reverse the current/Hall probe and average 8. ln B = –αp + ln kNI 9. Relationship is valid if the graph is a straight line. 10. Calibrate Hall probe using a known field.

Page 4 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9702 52 © UCLES 2016 Question Answer Marks 2 (a) gradient = q y-intercept = lg p 1 (b) 2.80 or 2.799 or 2.7993 0.28 or 0.279 2.79 or 2.792 or 2.7924 0.30 or 0.301 2.77 or 2.771 or 2.7709 0.36 or 0.362 2.72 or 2.716 or 2.7160 0.49 or 0.491 2.69 or 2.690 or 2.6902 0.57 or 0.568 2.67 or 2.672 or 2.6721 0.61 or 0.613 All first column correct – either 2 and 3 decimal places or 3 and 4 decimal places. All second column correct. Allow a mixture of decimal places. Uncertainties in lg (V / V) from ± 0.02 to ± 0.01. Allow more than one significant figure. 1 1 1 (c) (i) Six points plotted correctly. Must be within half a small square. No “blobs”. 1 All error bars in lg (V / V) plotted correctly. All error bars to be plotted. Total length of bar must be accurate to less than half a small square and symmetrical. 1 (ii) Line of best fit drawn. Line must not be drawn from top point to bottom point unless points are balanced. Upper end of line should pass between (2.694, 0.55) and (2.700, 0.55) and lower end of line should pass between (2.770, 0.35) and (2.776, 0.35). 1 Worst acceptable line drawn correctly. Steepest or shallowest possible line that passes through all the error bars. Mark scored only if all error bars are plotted. 1 (iii) Gradient determined with a triangle that is at least half the length of the drawn line. Read-offs must be accurate to half a small square. Gradient must be negative. 1 Method of determining absolute uncertainty. uncertainty = gradient of line of best fit – gradient of worst acceptable line or uncertainty = ½(steepest worst line gradient – shallowest worst line gradient) 1

Page 5 Mark Scheme Syllabus Paper Cambridge International AS/A Level – October/November 2016 9702 52 © UCLES 2016 Question Answer Marks (iv) y-intercept determined by substitution into y = mx + c. Read-offs must be accurate to half a small square. 1 Method of determining absolute uncertainty. uncertainty = y-intercept of line of best fit – y-intercept of worst acceptable line or uncertainty = ½(steepest worst line y-intercept – shallowest worst line y-intercept) No ECF from false origin method. 1 (d) Use of p = 10answer to 2(c)(iv) or lg p = answer to 2(c)(iv) 1 q = gradient and in the range –2.50 to –2.70 and given to 2 or 3 s.f. 1 (e) Use of V = p × 950q or lg V = q lg 950 + lg p or lg V = q lg 950 + y-intercept Correct substitution of numbers must be seen to give V. 1