Cambridge IGCSE Physics 0625 — 2015 Oct/Nov Paper 6 · Variant 1

1 The class is investigating two different types of pendulum. Figs. 1.1 and 1.2 show the apparatus used. clamp clamp 0 cm mark pivot 1.0 cm mark string l rule bob 50.0 cm mark Fig. 1.1 Fig. 1.2 (a) (i) On Fig. 1.1, measure the length l of the pendulum. l = ...........................................................[1] (ii) Explain briefly how you would measure the length l of a pendulum, of the type shown in Fig. 1.1, as accurately as possible. ........................................................................................................................................... .......................................................................................................................................[1] (b) A student adjusts the length l of the pendulum shown in Fig. 1.1 to be exactly 50.0 cm. She displaces the pendulum bob slightly and releases it so that it swings. She measures the time tS for 20 complete oscillations of the pendulum. (i) Record the time tS as shown in Fig. 1.3. PLQ V 00.28 20 Fig. 1.3 tS = ...........................................................[1] (ii) Calculate the period TS of the pendulum. The period is the time for one complete oscillation. TS = ...........................................................[1] (iii) Explain why measuring the time for 20 oscillations, rather than for 1 oscillation, gives a more accurate value for TS. ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[1] (c) The pendulum shown in Fig. 1.2 is a 50.0 cm rule. The student displaces this pendulum slightly and releases it so that it swings. She measures the time tC for 20 complete oscillations of the pendulum. tC = ................................................................23.2 s (i) State a precaution that you would take to ensure that the measurement of time tC is reliable. ........................................................................................................................................... (ii) Calculate the period TC of the pendulum. The period is the time for one complete oscillation. TC = ............................................................... [1] (d) A student suggests that TC should be equal to TS. State whether the results support this suggestion. Justify your answer by reference to the results. statement .................................................................................................................................. justification ................................................................................................................................ ................................................................................................................................................... ................................................................................................................................................... [2] (e) Assume that the length l of the first pendulum has been measured accurately at 50.0 cm and that the length of the strip that forms the second pendulum is exactly 50.0 cm long. Suggest why it may not be correct to state that both pendulums have the same length l = 50.0 cm. ................................................................................................................................................... ...............................................................................................................................................[1] [Total: 9]

Mark scheme: 1 (a) (i) 4.2 (cm) OR 42 (mm) [1] (ii) centre of bob touching rule OR how to use fiducial aid, e.g. set-square OR measure to top / bottom of bob and add / subtract radius OR measure to top and bottom of bob and average OR look perpendicularly at scale [1] (b) (i) 28.2(0) (s) [1] (ii) 1.41(s) (e.c.f. from (i) AND TC = 1.16(s)) [1] (iii) (reaction time) inaccuracy – smaller part of total time measured owtte [1] (c) (i) repeats OR start counting at nought OR use a fiducial mark owtte [1] (ii) see (b)(ii) (d) correct statement for results [1] justification must include idea of too different to be within limits of experimental accuracy (e.c.f. close enough to be within limits of experimental accuracy) [1] (e) pivot at 1 cm mark owtte OR centre of mass of rule not 50 cm below pivot [1] [Total: 9]

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2 The class is determining the resistance of a resistor. Fig. 2.1 shows the circuit. power supply A resistance wire l R A B sliding V contact C Fig. 2.1 (a) A student places the sliding contact C at a distance l from end A of the resistance wire. She records the reading on the voltmeter. (i) Read the meter shown in Fig. 2.2. Record, in Table 2.1, this value of V for length l = 100 cm. 4 5 6 0.4 0.6 3 7 2 8 0.2 0.8 1 9 0 10 0 1.0 V A Fig. 2.2 Fig. 2.3 Table 2.1 l / cm V / V 20.0 1.1 40.0 1.4 60.0 1.6 80.0 1.9 100.0 [1] (ii) Read the meter shown in Fig. 2.3. Record this current I. I = ...........................................................[1] (b) Plot a graph of V / V (y-axis) against l / cm (x-axis). Start both axes at the origin (0, 0). [4] (c) (i) Determine the value of the intercept Y on the y-axis. Y = ...........................................................[1] Y (ii) Calculate the ratio . The value of I is your answer to part (a) (ii). I Y = ............................................................... I Y (iii) I is numerically equal to the resistance R of the resistor R. Write down a value for R to a suitable number of significant figures for this experiment. Include the unit. R = ............................................................... [2] [Total: 9]

Mark scheme: 2 (a) (i) V = 2.2 (V) [1] (ii) I = 0.2(0) (A) [1] (b) graph: • axes both correctly labelled, right way round and with units [1] • suitable scales, to include origin [1] • all plots correct to within ½ small square [1] • good best-fit line judgement, single, thin, continuous line [1] (c) (i) intercept correct to ½ small square [1] (ii) ratio correct AND R value equal to ratio, ignore any unit, e.c.f. allowed [1] (iii) 2 or 3 sig. figs. AND unit of Ω [1] [Total: 9]

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3 The class is investigating reflection using a plane mirror. Fig. 3.1. shows a student’s ray-trace sheet. M R P3 P4 eye ray-trace sheet Fig. 3.1 (a) The student draws the line MR to mark the position of a plane mirror. (i) Draw a normal to this line that passes through its centre. Label the normal NL. Label the point at which NL crosses MR with the letter A. (ii) Draw a line 8.0 cm long from A at an angle of incidence i = 30° to the normal, below MR and to the left of the normal. Label the end of this line B. [3] (b) The student places a pin P1 at point B. He places a second pin P2 on line AB. Label a position X on line AB to show a suitable position for pin P2. [1] (c) He views the images of pins P1 and P2 from the direction indicated by the eye in Fig. 3.1. He places two pins P3 and P4, a suitable distance apart, so that pins P3 and P4, and the images of P2 and P1, all appear exactly one behind the other. The positions of P3 and P4 are shown in Fig. 3.1. (i) Draw the line joining the positions of P3 and P4. Extend the line until it meets NL. (ii) Measure the angle r between NL and the line joining the positions of P3 and P4. r = ............................................................... [2] (d) State two precautions that you would take in this experiment in order to obtain reliable readings. 1. ............................................................................................................................................... ................................................................................................................................................... 2. ............................................................................................................................................... ................................................................................................................................................... [2] (e) A student has done this experiment very carefully, taking these precautions. She is disappointed to find that her line for the reflected ray is not exactly where she predicts from the theory. Suggest a practical reason for this. ................................................................................................................................................... ...............................................................................................................................................[1] [Total: 9]

Mark scheme: 3 (a)(i)(ii) ray-trace: • normal at 90° and crossing MR at intersection with P3P4 line [1] • incident ray at 30° ± 2° in correct quadrant [1] • incident ray 8.0 cm long [1] (b) B to X at least 5.0 cm [1] (c) (i) P3P4 line correctly drawn AND all lines single, thin, continuous lines [1] (ii) r =31(°)–33(°) [1] (d) any two from: • ensure pins are vertical / view bases of pins • pins far apart (or > 5 cm) • ensure mirror exactly on MR / ensure mirror does not move • thin lines / sharp pencil / thin pins • repeats [2] (e) any one from: • thickness of lines / pencil / mirror / pins • difficulty of lining up pins and images [1] [Total: 9]

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4 The class is investigating the cooling of water. Fig. 4.1 shows the apparatus used. thermometer water Fig. 4.1 (a) Record the temperature θC of the cold water shown on the thermometer in Fig. 4.2. °C 110 100 90 80 70 60 50 40 30 20 10 0 –10 Fig. 4.2 θC = ...........................................................[1] (b) A student pours 100 cm3 of hot water into a beaker. He records the temperature θH of the hot water in the beaker. θH = ................................................................83 °C State one precaution that you would take to ensure that the temperature reading is as reliable as possible. ................................................................................................................................................... ...............................................................................................................................................[1] (c) The student adds 100 cm3 of cold water to the hot water in the beaker. He records the temperature θM of the mixture. θM = ................................................................46 °C Calculate the average temperature θA of the hot water and the cold water using the equation (θH + θC) θA = . 2 θA = ............................................................... [1] (d) The student carried out this experiment carefully. He was expecting that the temperature θM of the mixture would be the same as the average temperature θA of the hot water and the cold water. Suggest two factors that could cause θM and θA to be different. 1. ............................................................................................................................................... ................................................................................................................................................... 2. ............................................................................................................................................... ................................................................................................................................................... [2] (e) Fig. 4.3 shows a measuring cylinder. Three students take the volume reading. Their readings are: • Student 1: 80 cm3 • Student 2: 79 cm3 • Student 3: 78 cm3 100 cm3 90 80 70 60 50 40 30 20 10 Fig. 4.3 (i) State the correct reading. correct reading = ............................................................... (ii) Explain briefly the mistake made by one of the other students. Student ................... is incorrect, because ........................................................................ ........................................................................................................................................... [2] [Total: 7]

Mark scheme: 4 (a) θC = 22 °C [1] (b) view thermometer at right angles OR stirring OR wait for reading to stop rising OR thermometer (bulb) not touching sides / bottom of beaker owtte [1] (c) θA = 52.5 (°C) OR e.c.f. [1] (d) any two from: • heat loss to surroundings / beaker OR heat loss / drop in temperature by evaporation • delays in taking readings • reference to uncertainty in volume measurements [2] (e) (i) 78 (cm3) [1] (ii) EITHER: Student 1 (80) – read to top of meniscus OR scale not read at right angles OR Student 2 (79) – divisions are every 2(cm3) not 1(cm3) OR Student 2 (79) – scale not read at right angles [1] [Total: 7]

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5 The class is doing a lens experiment. Fig. 5.1 shows some of the apparatus used. lens illuminated object screen Fig. 5.1 (a) Draw a diagram to show how the apparatus shown in Fig. 5.1 is arranged for an experiment to determine the focal length of the lens. The laboratory bench is drawn for you. bench [2] (b) The focal length of the lens is known to be approximately 15 cm. Suggest a suitable distance d between the illuminated object and the screen so that a well-focused image can be seen on the screen. d = ..................................................... cm [1] (c) Suggest two practical difficulties that may cause inaccuracy in the value of focal length obtained. 1. ............................................................................................................................................... ................................................................................................................................................... 2. ............................................................................................................................................... ................................................................................................................................................... [2] (d) Fig. 5.2 shows the shape of the illuminated object. Fig. 5.2 In the space below, draw a diagram to show the focused image that you would expect to see on the screen. [1] [Total: 6]

Mark scheme: 5 (a) in correct order: object, lens, screen [1] all three components on bench and all perpendicular to bench [1] (b) 50–100 (cm) [1] (c) any two from: • difficulty in deciding exact position of lens for best image / image not quite clear owtte • difficulty in measuring to centre of lens • room too bright / lamp too dim [2] (d) image shown upside down [1] [Total: 6]

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