Cambridge IGCSE Physics 0625 — 2020 Oct/Nov Paper 6 · Variant 2

1 A student investigates the stretching of a spring. Fig. 1.1 shows the set up. metre rule spring clamp stand bench Fig. 1.1 (a) The metre rule is clamped in position near to the spring. On Fig. 1.1, show clearly how you would use a set square to obtain an accurate reading of the position of the bottom of the coiled part of the spring from the metre rule. [2] (b) Fig. 1.2 shows the spring drawn to actual size. On Fig. 1.2, measure the length L of the coiled part of the spring. Fig. 1.2 L = .................................................. mm [1] (c) The student adds a load P = 0.20 N to the spring. He records the new length l of the coiled part of the spring. He repeats the procedure using loads P = 0.40 N, 0.60 N, 0.80 N and 1.00 N. All the readings are recorded in Table 1.1. Table 1.1 P / N l / mm 0.20 20 0.40 26 0.60 31 0.80 35 1.00 41 Plot a graph of l / mm (y-axis) against P / N (x-axis). Start both axes at the origin (0,0). [4] (d) The intercept on the y-axis of the graph is numerically equal to the length l0 of the spring when P = 0. Determine the value of l0. Show clearly on the graph how you obtained the necessary information. l0 = ......................................................... [2] (e) Calculate L – l0. L – l0 = ......................................................... [2] [Total: 11]

Mark scheme: 1(a) clear diagram showing a horizontal line (of set square across from spring to metre rule) 1 drawn to bottom of spring 1 1(b) 14 / 14.5 / 15 (mm) 1 1(c) graph 1 axes correctly labelled and right way round 1 all plots correct to ½ small square 1 good line judgement, thin, continuous line 1 1(d) intercept method clearly shown 1 l 0 value correctly read to ½ small square 1 1(e) L – l 0 correct calculation 1 L – l 0 = 0 ± 2 (mm) 1

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2 A student investigates the refraction of light in a transparent block. Fig. 2.1 shows her ray-trace sheet. She places a transparent block on the ray-trace sheet and draws the outline ABCD of the block. The student uses pins to mark the positions of objects and images. A B D C P3 P4 eye Fig. 2.1 (a) • On Fig. 2.1, draw the normal NL at the centre of side AB. Continue the normal NL so that it passes through side CD of the block. • Label the point F where the normal NL crosses side AB. • Label the point G where the normal NL crosses side CD. [1] (b) • On Fig. 2.1, draw a line EF at least 7 cm long above side AB and at an angle i = 30° to the left of the normal. Label the end of the line E. • Mark the positions of two pins P1 and P2, to act as objects, on line EF at a suitable distance apart for this type of ray-trace experiment. [1] (c) • The student looks from the position of the eye shown in Fig. 2.1, to observe the images of P1 and P2 through side CD of the block. She adjusts her line of sight until the images of P1 and P2 appear one behind the other. • She places two pins P3 and P4 between her eye and the block so that P3, P4 and the images of P1 and P2, seen through the block, appear one behind the other. • The positions of P3 and P4 are marked on the ray-trace sheet. (i) Draw a line joining the positions of P3 and P4. Continue the line through the block until it extends to just outside the outline of the block. Label this end of the line K. [1] (ii) • Label the point H where the line in (c)(i) meets side CD. • Label the point J where the line meets the normal NL. • Draw the line FH. [1] (iii) Measure and record the length a of the line GH. a = ............................................................... Measure and record the length b of the line FH. b = ............................................................... [1] (d) Measure and record the acute angle θ between the line JF and the line JK. An acute angle is less than 90°. θ = ......................................................... [2] (e) State one precaution that you would take in order to produce an accurate ray-trace. ................................................................................................................................................... ............................................................................................................................................. [1] (f) A student suggests that i should be equal to θ within the limits of experimental accuracy. In this experiment, i = 30°. Suggest a range of values for θ that match this suggestion for the experiment. range .................................................................................................................................. [1] (g) A student plans to test the suggestion that, in this experiment, i = θ for all possible values of i. Explain briefly how you would test the suggestion. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] [Total: 11]

Mark scheme: 2(a) normal in centre of AB to 2 mm and at 90° and F and G correctly labelled 1 2(b) P1P2 pin separation at least 5.0 cm 1 2(c)(i) line through P3 and P4 correctly drawn and its end labelled K 1 2(c)(ii) points H and J correctly labelled, and FH correctly drawn 1 2(c)(iii) a = 1.3 ± 0.1 cm and b = 4.2 ± 0.1 cm 1 2(d) candidate’s θ correct to ± 2(°) 1 unit 1 2(e) any one from: thin lines / pins / sharp pencil view bases of pins ensure pins vertical / perpendicular to ray trace sheet use large pin separation (securely) attach the ray trace sheet to the surface 1 2(f) maximum range 27(°) – 33(°) 1 2(g) repeat experiment using more i values 1 uses at least 4 i values 1

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3 A student is investigating the resistance of samples of wire. Fig. 3.1 shows the circuit used. power supply A resistance wire C D B E V Fig. 3.1 Table 3.1 shows how the samples of wire are connected into the circuit. Table 3.1 section wire BC one 30 cm piece CD two 30 cm pieces DE three 30 cm pieces (a) (i) Record the potential difference (p.d.) V1 across section BC of the resistance wire, as shown on the voltmeter in Fig. 3.2. 2 3 0.4 0.6 1 4 0.2 0.8 0 5 0 1.0 V A Fig. 3.2 Fig. 3.3 V1 = ......................................................... [1] (ii) Record the current I in the circuit, as shown in Fig. 3.3. I = ......................................................... [1] (iii) Calculate the resistance R1 of the section BC of the resistance wire. Use the equation V1 R1 = . Give your answer to a suitable number of significant figures for this experiment. I R1 = ......................................................... [1] (b) The student connects the voltmeter across section CD. He records the potential difference (p.d.) V2 across section CD. 0.70 V2 = ............................................................... He calculates the resistance R2 of section CD. 1.25 R2 = ............................................................... He connects the voltmeter across section DE. He records the potential difference (p.d.) V3 across section DE. 0.46 V3 = ............................................................... V3 Calculate the resistance R3 of section DE using the equation R3 = . Use the value of I from I (a)(ii). Give your answer to a suitable number of significant figures for this experiment. R3 = ......................................................... [1] (c) Complete the student’s recorded readings by including the units in (b). [1] (d) The sections BC, CD and DE are all the same length and made of the same metal. (i) Tick the box to show your conclusion from the results. The resistance of a section increases as the number of wires increases The resistance of a section decreases as the number of wires increases The resistance of a section is independent of the number of wires. [1] (ii) Justify your conclusion in (d)(i) by reference to the results. ........................................................................................................................................... ..................................................................................................................................... [1] (e) Explain how you would change this experiment to investigate the relationship between the length of a sample of wire and its resistance. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (f) A student repeats the investigation in (a) to (d), but uses different values of current I. He has a power source with a single fixed output potential difference. (i) Name the component he could connect into the circuit to vary the current. ..................................................................................................................................... [1] (ii) Draw the circuit symbol for this component. [1] [Total: 11]

Mark scheme: 3(a)(i) V1 = 1.4(0) (V) 1 3(a)(ii) I = 0.56 (A) 1 3(a)(iii) R1 = 2.5(0) (Ω) 1 3(b) R3 = 0.82 (Ω) 1 3(c) V, Ω, V 1 3(d)(i) second box ticked 1 3(d)(ii) correct justification using results 1 3(e) use different lengths (of the wire sample) 1 measure the p.d. and current / determine the resistance (of each length) 1 3(f)(i) variable resistor / resistance / rheostat 1 3(f)(ii) correct circuit symbol for a variable resistor 1

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4 A student investigates the length of time taken for ice cubes to melt when they are placed in water. She uses beakers of water at different temperatures to investigate how the initial temperature of the water affects the time taken for the ice cubes to melt. Plan an experiment to investigate how the initial temperature of the water affects the time taken for the ice cubes to melt. The following apparatus is available: thermometer supply of ice cubes 250 cm3 beakers supply of cold water In your plan, you should: • write a list of additional apparatus to use • explain how to carry out the investigation • state the key variables to keep constant • draw a table, or tables, with column headings, to show how to display the readings (you are not required to enter any readings in the table) • explain how to use the readings to reach a conclusion. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7] [Total: 7]

Mark scheme: 4 Apparatus: MP1 method of heating water and timer 1 MP2 method: measure the temperature of the water and then place the ice cube(s) in the water and measure the time taken to melt 1 MP3 method: melt repeat with water at different temperature(s) 1 Key variables: Any two from: MP4 mass / volume of ice cubes MP5 number / size of ice cubes (per test) temperature of ice cubes / keep ice cubes in freezer volume / amount of water in the beaker room temperature amount of stirring 2 Table: MP6 table with columns for time / t and water temperature with correct units 1 Conclusion: MP7 explanation of how to reach a conclusion 1 Additional graph notes: Note: The principle to apply here is ‘could I draw a significantly better line, using these points, under examination conditions?’ If the answer is definitely ‘yes’, do not award the mark. Note: If candidate’s scale consists of actual readings at equal intervals this will produce a perfect straight line! The only mark available in this case is the first (axes right way round and labelled) So maximum 1. If axes are wrong way round, the other 3 marks are still available.

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