Cambridge IGCSE Physics 0625 — 2017 May/June Paper 5 · Variant 3

1 In this experiment, you will investigate the resistance of a power supply. The circuit has been set up for you. Carry out the following instructions, referring to Fig. 1.1. power supply A P V Q X resistance wire crocodile clip Fig. 1.1 (a) • Connect the crocodile clip near end X of the resistance wire. • Switch on. • Adjust the position of the crocodile clip until the potential difference V across terminals P and Q is 2.0 V. • Record, in Table 1.1, the value of the current I shown on the ammeter. • Move the crocodile clip and record values of I for V = 1.8 V, 1.6 V, 1.4 V and 1.2 V. • Switch off. Table 1.1 I / A V / V 2.0 1.8 1.6 1.4 1.2 [2] (b) Plot a graph of V / V (y-axis) against I / A (x-axis). [4] (c) (i) Determine the gradient M of the graph. Show clearly on the graph how you obtained the necessary information. M = .......................................................... [1] (ii) The gradient M is numerically equal to the resistance R of the power supply. Write down the resistance R to a suitable number of significant figures for this experiment. R = .......................................................... [2] (d) Suggest one practical reason why the crocodile clip should not be connected to very short lengths of resistance wire in order to obtain smaller potential differences. ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[1] (e) In this type of experiment, it is possible to change the potential difference by using a variable resistor rather than using different lengths of a resistance wire. In the space, draw the standard circuit symbol for a variable resistor. [1] [Total: 11]

Mark scheme: 1(a) 1 all < 5.00 A and to 2dp at least 1 1(b) graph: axes labelled with quantity and unit 1 appropriate scales (plots occupying at least ½ grid) 1 plots all correct to ½ small square 1 Well-judged straight line and thin line, precise plots 1 1(c)(i) M present and triangle method seen on graph 1 1(c)(ii) R in range 0.5 to 4.0 Ω 1 2 or 3 sig figs and unit = Ω 1 1(d) suitable reason: e.g.: wire becomes too hot, current exceeds full scale deflection(owtte) of meter/becomes too large 1 1(e) correct symbol for variable resistor (rectangle with strike-through arrow only) 1 Total: 11

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2 In this experiment, you will determine the density of water by two methods. Method 1 Carry out the following instructions, referring to Figs. 2.1 and 2.2. forcemeter loop of string modelling clay measuring cylinder Fig. 2.1 Fig. 2.2 (a) Measure the weight W1 of the piece of modelling clay, as shown in Fig. 2.1. W1 = ....................................................... N [1] (b) (i) Pour approximately 150 cm3 of water into the measuring cylinder. Record the volume V1 of the water in the measuring cylinder. V1 = ................................................... cm3 [1] (ii) Describe briefly how a measuring cylinder is read to obtain an accurate value for the volume of water. You may draw a diagram. ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[2] (c) Lower the piece of modelling clay into the water as shown in Fig. 2.2. • Record the new reading W2 of the forcemeter. W2 = ............................................................ N • Record the new reading V2 of the measuring cylinder, with the piece of modelling clay in the water. V2 = ........................................................ cm3 • Remove the modelling clay from the measuring cylinder. • Do not empty the measuring cylinder. [1] (d) Calculate a value ρ1 for the density of water, using your readings from (a), (b) and (c) and the equation (W1 – W2) ρ1 = × k (V2 – V1) where k = 100 g / N. ρ1 = ...........................................................[2] Method 2 (e) • Measure the mass m1 of the measuring cylinder, still containing the volume V1 of water. Use the balance provided. m1 = ............................................................... • Empty the measuring cylinder. • Measure the mass m2 of the empty measuring cylinder. m2 = ............................................................... [1] (f) Calculate a second value ρ2 for the density of water, using your readings from (b) and (e) and the equation (m1 – m2) ρ2 = . V1 ρ2 = .......................................................... [1] (g) Suggest a possible source of inaccuracy in either Method 1 or Method 2, even when they are carried out carefully. Explain how an improvement might be made to reduce this inaccuracy. suggestion ................................................................................................................................ ................................................................................................................................................... explanation of improvement ..................................................................................................... ................................................................................................................................................... ................................................................................................................................................... [2] [Total: 11]

Mark scheme: 2(a) sensible value for W1 (0.7 to 1.3 N) 1 2(b)(i) sensible value for V1 (140 to 160 cm3) 1 2(b)(ii) line of sight perpendicular 1 to bottom of meniscus 1 2(c) W2 < W1 and V2 > V1 1 2(d) correct calculation of ρ1 1 unit g / cm3 1 2(e) m1 > m2 by between 100 g and 200 g 1 2(f) ρ2 and ρ1 in range 0.9 to 1.1 1 2(g) appropriate cause of inaccuracy: e.g.: • some water still in empty measuring cylinder • water spilled, splashed when putty put in water water drops on putty when removed • air bubbles on putty 1 suitable improvement: e.g.: • measure m2 at start (when cylinder dry) • measure new volume in Method OR refill to correct value • shake putty to remove air / smooth surface to minimise bubbles 1 Total: 11

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3 In this experiment, you will investigate the refraction of light by a transparent block. You will determine a quantity known as the refractive index of the material of the block. Carry out the following instructions, using the separate ray-trace sheet provided. You may refer to Fig. 3.1 for guidance. eye hole position Y F N i A L B ray-trace 1 cm sheet D C eye position X Fig. 3.1 (a) • Place the block approximately in the centre of the ray-trace sheet. Carefully draw round the block and label the corners ABCD, as indicated in Fig. 3.1. • Remove the block from the ray-trace sheet. • Draw a normal to line AB at a point L, 1 cm from A. Label the other end of the normal with the letter N. • Draw a line FL, 8 cm long and at an angle θ = 30°, as indicated by Fig. 3.1. [1] (b) • Replace the block in exactly the same position as in (a). • Place two pins P1 and P2 on line FL, a suitable distance apart for accurate ray tracing. • Label the positions of P1 and P2. • View the images of P1 and P2 through the block, from the direction indicated by the eye in position X in Fig. 3.1. Place two pins P3 and P4, a suitable distance apart, so that pins P3 and P4, and the images of P1 and P2, all appear exactly one behind the other. • Label the positions of P3 and P4. • Remove the block and pins from the ray-trace sheet. [1] (c) (i) • Draw a line joining P3 and P4. Extend this line until it meets CD. • Label the point at which this line meets CD with the letter G. • Draw a line through G, at 90° to CD. Extend this line until it crosses AB. • Label the point at which this line crosses AB with the letter H. • Extend line FL until it meets GH. • Label the point at which it meets GH with the letter K. • Join points L and G with a straight line. [1] (ii) • Measure the length a of line LG. a = ......................................................... cm • Measure the length b of line LK. b = ......................................................... cm • Calculate a value n for the refractive index, using the equation n = . a–b n = ............................................................... [3] (d) • Replace the block in exactly the same position as in (a). • Replace the two pins P1 and P2 on line FL. • Place the mirror against side CD, with the reflecting surface towards the block. • View the images of P1 and P2 from the direction indicated by the eye in position Y in Fig. 3.1. Place two pins P5 and P6, a suitable distance apart, so that pins P5 and P6, and the images of P1 and P2, all appear exactly one behind the other. • Label the positions of P5 and P6. • Remove the block and pins from the ray-trace sheet. [1] (e) (i) • Draw a line joining P5 and P6. Extend this line until it meets GH. • Label the point at which this line meets GH with the letter M. • Label the other end of the line with the letter R. • Measure the angle α, where α is the smaller angle between lines RM and GH. α = .......................................................... [1] (ii) A student suggests that angle α and angle θ, measured in part (a), should be equal. State whether your results support this suggestion. Justify your answer with reference to your results. statement .......................................................................................................................... justification ........................................................................................................................ ........................................................................................................................................... [2] (f) Suggest why different students, all carrying out this experiment carefully, may not obtain identical results. ................................................................................................................................................... ...............................................................................................................................................[1] [Total: 11] Tie your ray-trace sheet into this Question Paper between pages 8 and 9.

Mark scheme: 3(a) 1 3(b) pin separation ⩾ 5 cm 1 3(c)(i) first set of lines in correct place 1 3(c)(ii) a and b lengths correct 1 n calculation correct 1 in range 1.3 to 1.7 and no unit 1 3(d) all lines present and neat 1 3(e)(i) α = 30° ± 3° 1 3(e)(ii) statement matching results 1 justification using values and matching the statement (‘within limits of experimental Accuracy’/owtte) 1 3(f) difficulty in aligning pins/placing pins accurately, pins (too) thick 1 Total: 11

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4 Plan an experiment to investigate how increasing the number of layers of insulation affects the rate of cooling of hot water in a beaker. You are not required to carry out the experiment. Write a plan for the experiment, including: • the apparatus needed • what you would measure • the variables you would keep the same to ensure the comparison is a fair test • instructions for carrying out the experiment • how you would present your results • how you would use your readings to reach a conclusion. 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Mark scheme: 4 MP1 apparatus beaker with insulation and thermometer and stopclock (or alternative) mentioned 1 MP2 method pour hot water into container measure temperature of hot water over period of time 1 MP3 repeat for additional layers 1 MP4 results: suitable table/graph/cooling curve 1 MP5 control variables any pair from: same initial temperature, same volume of water, same size/material/thickness of beaker, same thickness of each layer, 1 MP6 MP7 additional points any 2 from: how cooling rate calculated/how to compare cooling curves, read thermometer perpendicularly, thermometer at same depth (for repeat) thermometer not touching beaker, stir before reading thermometer, use of lid, minimum of 5 different thicknesses of insulation, repeat experiment with different sized beakers/different amount of water, sensible amount of water (50 cm3 to 500 cm3) 2 Total: 7

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