Cambridge IGCSE Physics 0625 — 2015 Oct/Nov Paper 5 · Variant 3

1 In this experiment, you will investigate the resistance of identical wires connected in parallel. The circuit has been set up for you as shown in Fig. 1.1, with crocodile clip A connected to the right-hand end of wire A. Carry out the following instructions, referring to Fig. 1.1. SRZHU VXSSO\ $ $ % & ZLUH $ ZLUH % FURFRGLOH FOLSV ZLUH & Fig. 1.1 (a) (i) On Fig. 1.1, use the appropriate symbol to show a voltmeter connected to measure the potential difference across wire A. [1] (ii) Connect the voltmeter in this position. (b) (i) Switch on. Measure, and record in Table 1.1, for wire A, the potential difference V and the current I in the circuit. Switch off. Table 1.1 wire V / V I / A combination A A and B A, B and C [3] (ii) Without disconnecting crocodile clip A, connect crocodile clip B to the right hand end of wire B. It does not matter if crocodile clips A and B touch. Repeat step (b)(i) for this combination of wires, A and B in parallel. (iii) Without disconnecting crocodile clips A or B, connect crocodile clip C to the right hand end of wire C. It does not matter if the crocodile clips touch. Repeat step (b)(i) for this combination of wires, A, B and C in parallel. (c) Calculate the resistance R of each wire combination, using the equation R = V . I resistance of wire A R1 = ............................. resistance of wires A and B in parallel R2 = ............................. resistance of wires A, B and C in parallel R3 = ............................. [3] (d) (i) A student suggests that when 2 identical wires are connected in parallel, their resistance should be equal to 1 of the resistance of a single wire. 2 State whether your findings agree with this suggestion. Justify your answer by reference to your results, giving values to support your justification. statement .......................................................................................................................... ........................................................................................................................................... justification ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [2] (ii) Use your results to suggest the relationship that should exist between R3 and R1. ........................................................................................................................................... .......................................................................................................................................[1] [Total: 10]

Mark scheme: 1 (a) (i) correct symbol for voltmeter shown AND shown connected in parallel [1] (b) (i)(ii)(iii) table: • p.d. values all < 3.0 V [1] • current values all < 1.00 A AND increasing [1] • p.d. values to at least 1 d.p., AND currents to at least 2 d.p. [1] (c) R calculations correct AND decreasing [1] correct unit (symbol or word) [1] consistently 2 sig. figs. or consistently 3 sig. figs. [1] (d) (i) statement matches results with any relevant values quoted [1] justification matching statement [1] (ii) R3 should be 1/3 × R1 owtte [1] [Total: 10]

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2 In this experiment, you will investigate the refraction of light in 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. 2.1 for guidance. KROH H\H 1 WUDQVSDUHQW EORFN ' $ % & / Fig. 2.1 (a) Draw a line approximately 12 cm long and about 6 cm from the bottom of the ray-trace sheet. Label this line AB. Draw a normal to AB at its centre. Extend the normal for at least 15 cm above AB towards the top of the sheet. Label the normal NL. Label the point at which NL crosses AB with the letter C. (b) Place the transparent block so that its long side is on line AB, as shown in Fig. 2.1. (c) (i) Carefully draw around the block. (ii) Place a pin P1 at point C. (iii) View the image of P1 through the block, from the direction indicated by the eye in Fig. 2.1. Place two pins P2 and P3 , a suitable distance apart, so that pins P2 and P3 and the image of P1 all appear exactly one behind the other. Label the positions of P2 and P3. (iv) Remove the block and pins from the ray-trace sheet. (v) Label the point at which NL crosses the top edge of the block with the letter D. (vi) Draw a line joining the positions of P2 and P3. Extend this line until it crosses NL. Label the point at which the line crosses NL with the letter E. (d) (i) Measure the length a of line DC. a = ............................................................... (ii) Measure the length b of line DE. b = ............................................................... [2] (iii) Calculate a value n1 for the refractive index of the block, using your values from (d)(i) and a (d)(ii) and the equation n1 = . b n1 = ...........................................................[1] Question 2 continues on the next page. (e) (i) Place the block so that its shorter side is on line AB, as shown in Fig. 2.2. 1 ) WUDQVSDUHQW EORFN $ % & / Fig. 2.2 (ii) Repeat steps (c)(i) to (c)(iv). (iii) Label the point at which NL crosses the top edge of the block with the letter F. (iv) Draw a line joining the new positions of P2 and P3. Extend this line until it crosses NL. Label the point at which the line crosses NL with the letter G. (f) (i) Measure the length c of line FC. c = ............................................................... (ii) Measure the length d of line FG. d = ............................................................... (iii) Calculate a second value n for the refractive index of the block, using your values from 2 c (f)(i) and (f)(ii) and the equation n2 = . d n2 = ............................................................... [1] (g) A student suggests that a third value for the refractive index could be obtained by repeating the experiment with the block standing on edge, as shown in Fig. 2.3. You are not required to carry out this experiment. 1 WUDQVSDUHQW EORFN $ % & / Fig. 2.3 State and explain whether this third value for the refractive index is likely to be more or less reliable than the other two values for the refractive index. statement .................................................................................................................................. explanation ............................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... [2] Tie your ray-trace sheet into this Booklet between pages 6 and 7. [4] [Total: 10]

Mark scheme: 2 ray-trace: • normal correct, near centre of AB [1] • first pin distance at least 5.0 cm [1] • first refracted line in correct place [1] • second refracted line in correct place AND all lines thin, continuous and straight [1] (d)(i)(ii) one measurement of a or b correct AND unit of cm or mm [1] both measurements correct AND unit of cm or mm [1] (iii) n1 calculation correct and in range 1.3–1.8 [1] (f) (i)(ii)(iii) c and d present AND n2 within 10% of n1 AND no unit for n1 or n2 [1] (g) less reliable AND reference to smaller block depth owtte [1] measuring smaller lengths gives greater (%) uncertainties owtte [1] [Total: 10]

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3 In this experiment, you will investigate the behaviour of a spring, and then use the spring to determine the weight of an object. The stand and spring have been set up. You are provided with an object X and a set of loads which will be used to stretch the spring. Carry out the following instructions, referring to Fig. 3.1. FODPS l VSULQJ ORDG Fig. 3.1 (a) (i) Hang a load of weight L = 1.0 N on the spring. Measure, and record in Table 3.1, the stretched length l of the spring, as indicated in Fig. 3.1. (ii) Describe a precaution that you took when measuring the length of the spring, to ensure a reliable reading. You may draw a diagram. ........................................................................................................................................... .......................................................................................................................................[1] (iii) Repeat step (a)(i) for L values of 2.0 N, 3.0 N, 4.0 N and 5.0 N. (iv) Remove the load from the spring. Table 3.1 L / N l / cm 1.0 2.0 3.0 4.0 5.0 [1] (b) Plot a graph of l / cm (y-axis) against L / N (x-axis). 0 0 [4] (c) Use your graph to determine the length l of the spring with no load attached. 0 l = ...........................................................[1] 0 (d) (i) Suspend object X from the spring and measure the stretched length l of the spring. l = ............................................................... (ii) Use the graph, and your reading from (d)(i), to determine the weight W of object X. Show clearly on the graph how you obtained your answer. W = ............................................................ N [2] (e) A student measures the weight of a different load using this same method. He gives the weight as 2.564 N. Explain why this is not a suitable number of significant figures for this experiment. ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[1] [Total: 10]

Mark scheme: 3 (a) (ii) any one from: [1] • clamp rule • rule close to spring • ensure rule vertical • avoidance of parallax errors (explained) • use of set square / fiducial aid (iv) l in cm and increasing [1] (b) graph: • axes both correctly labelled, with quantities and units [1] • suitable scales [1] • plots correct to within ½ small square [1] • good best-fit straight line, single, thin, continuous line [1] (c) l0 matches candidate’s graph [1] (d)(i)(ii) l recorded AND W in range 3.0 to 3.8(N) [1] indication on graph which matches candidate’s values [1] (e) any one from: [1] • data only to 2 sig. figs. • cannot plot / read graph to that accuracy • cannot read rule to that accuracy [Total: 10]

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4 In this experiment, you will investigate the transfer of thermal energy. Carry out the following instructions, referring to Fig. 4.1. thermometers boiling beaker tube Fig. 4.1 (a) (i) Pour 40 cm3 of cold water into the boiling tube. Record, in the first row of Table 4.1, the temperature θC of the cold water. (ii) Pour 300 cm3 of hot water into the beaker. Record, in the first row of the table, the temperature θH of the hot water. (iii) Lower the boiling tube into the beaker of hot water and immediately start the stopclock. Record, in the table, the temperature θC of the cold water and the temperature θH of the hot water at times t = 30 s, 60 s, 90 s, 120 s, 150 s and 180 s. Table 4.1 boiling tube with 40 cm3 boiling tube with 20 cm3 of cold water of cold water t / θC / θH / θC / θH / 0 30 60 90 120 150 180 [4] (b) (i) Carefully pour away the water from the boiling tube and the beaker. Make sure that the boiling tube is secure in the clamp. Pour 20 cm3 of cold water into the boiling tube. Record its temperature θC in the table. Repeat steps (a)(ii) and (a)(iii). (ii) Complete the column headings in the table. (c) Write a conclusion stating how the quantity of cold water in the boiling tube affects its temperature rise. ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[1] (d) Another student wishes to check your conclusion by repeating the experiment with 10 cm3 of cold water. Suggest two conditions which he should keep the same so that the comparison will be fair. 1. ............................................................................................................................................... ................................................................................................................................................... 2. ............................................................................................................................................... ................................................................................................................................................... [2] (e) Scientists in an industrial laboratory wish to use this experiment as a model of a heat exchanger, which transfers thermal energy between liquids. Suggest two different improvements to the apparatus which would make the heating of the cold water more efficient. For your first suggestion, explain why it would be an improvement. suggestion 1 ............................................................................................................................. explanation ............................................................................................................................... ................................................................................................................................................... suggestion 2 ............................................................................................................................. [3] [Total: 10]

Mark scheme: 4 table: • boiling tube with 40 cm3, θC increasing [1] • boiling tube with 20 cm3, θC increasing at greater rate [1] • both θH decreasing AND all θ values to at least 1 oC [1] • units correct and consistent (symbols or words) [1] (c) conclusion which matches temperature changes [1] (d) any two from: • volume / level of hot water • initial temperature of hot water • initial temperature of cold water • same type of boiling tube • room temperature / draughts / appropriate environmental condition [2] (e) any two improvements relating to apparatus: [2] • lid on beaker • insulation on beaker • lid / cotton wool in boiling tube • thinner / metal walls on tube • all cold water in boiling tube below hot water level • greater contact area of tube • use of water bath explanation matching first improvement, including: [1] • reduces loss of thermal energy from beaker • reduces loss of thermal energy from boiling tube • better thermal conduction • not affected by variation in hot water temperature [Total: 10]

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