Cambridge IGCSE Physics 0625 — 2021 May/June Paper 6 · Variant 3

1 A student investigates the behaviour of a spring, and then uses the spring to determine the density of modelling clay. The apparatus is shown in Fig. 1.1. clamp spring load Fig. 1.1 (a) Describe two precautions that the student should take when measuring the length of the spring, to ensure an accurate reading. You may draw a diagram. 1. ............................................................................................................................................... ................................................................................................................................................... 2. ............................................................................................................................................... ................................................................................................................................................... [2] (b) The student measures the length l 0 of the spring without any load. 2.3 l 0 = ......................................................cm A load of weight W = 2.0 N is suspended from the spring, as shown in Fig. 1.2. clamp spring l 2.0 N load Fig. 1.2 (i) On Fig. 1.2, measure the stretched length l of the spring. l = ................................................ cm [1] (ii) Calculate the extension e of the spring for a load of weight W = 2.0 N. Use the equation e = (l – l 0). e = ................................................ cm [1] (c) The 2.0 N load is removed from the spring. A load U is made of modelling clay wrapped on a wire hanger. Load U is suspended from the spring. The student measures the stretched length l U of the spring. 7.4 l U =.......................................................cm Calculate the extension eU of the spring with load U. eU = ......................................................cm The extension of a spring is directly proportional to the weight of the load. Use your values of W and e from (b)(ii) and your value of eU to determine the weight WU of load U. Show your working. WU = ........................................................... [2] (d) Load U is fully immersed in a beaker of water, as shown in Fig. 1.3. clamp spring lW wire hanger beaker load U bench water Fig. 1.3 On Fig. 1.3, measure the stretched length l W of the spring. l W = ......................................................cm Calculate the extension e W of the spring with load U in the water. e W = ......................................................cm Calculate the density ρ of the modelling clay. Use your values of eU from (c), your value of e W and the equation eU ρ = × k , where k = 1.0 g / cm3. (eU – e W) ρ = ................................................ g / cm3 [2] (e) Suggest a possible source of inaccuracy in the determination of ρ in this experiment. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [1] (f) The student plots a graph of load against extension for the spring, to show that the two quantities are directly proportional. State how his graph line shows that load and extension are directly proportional. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] [Total: 11]

Mark scheme: 1(a) any 2 valid precautions e.g: rule close rule parallel to spring eye perpendicular to reading use set square clamp rule 2 1(b)(i) l = 10.7 (cm) 1 1(b)(ii) e = 8.4 / ecf (cm) 1 1(c) eU present 1 WR = 1.2 and unit (N) correct working shown 1 1(d) lW and ew present 1 ρ = 1.5 (g / cm3) given to 2/3 significant figures 1 1(e) any valid source of inaccuracy e.g: part of load U is metal hanger immersed too clay wet when weight measured air holes in clay air bubbles on immersed clay 1 1(f) straight line 1 stated as going through origin 1

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2 A student determines the electromotive force (e.m.f.) and resistance of a cell by using a resistance wire. She uses the circuit shown in Fig. 2.1. power supply + – resistance wire A crocodile clip P Q resistor Fig. 2.1 (a) On Fig. 2.1, draw a voltmeter connected to measure the potential difference (p.d.) across terminals P and Q. [1] (b) The switch is closed. The student moves the crocodile clip on the resistance wire so that the potential difference V across terminals P and Q is 5.0 V. She measures the current I for the cell and resistor in series. 0.4 0.6 0.2 0.8 0 1.0 A Fig. 2.2 Read, and record in Table 2.1, the value of I shown on the meter in Fig. 2.2. [1] (c) The student repeats the procedure in (b) for values of V = 4.5 V, 4.0 V, 3.5 V and 3.0 V. Her readings are shown in Table 2.1. Table 2.1 V / V I / A 5.0 4.5 0.56 4.0 0.44 3.5 0.35 3.0 0.28 Plot a graph of I / A (y-axis) against V / V (x-axis). Start both axes at the origin (0,0). 0 0 [4] (d) The e.m.f. E of the cell is equal to the value of V when I = 0.0 A. Determine the value of E from the graph. E = ..................................................... [1] (e) (i) Determine the gradient G of the graph. Show clearly on the graph how you obtained the necessary information. G = ..................................................... [1] 1 (ii) The value of is numerically equal to the resistance (r + R) where r is the resistance of G the cell and R = 4.0 Ω. Calculate the resistance r of the cell. r = .................................................. Ω [1] (f) Suggest how the experiment and graph could be improved to obtain a more accurate value for e.m.f. E. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] [Total: 11]

Mark scheme: 2(a) correct voltmeter symbol in parallel with resistor and cell 1 2(b) IA = 0.64 (A) 1 2(c) graph: • axes labelled with quantity and unit 1 • appropriate scales (plots occupying at least 1 2 grid) 1 • plots all correct to 1 2 small square and precise plots 1 • well judged line and thin line 1 2(d) E in range 1.3 to 1.7 (V) 1 2(e)(i) G present and triangle method seen on graph 1 2(e)(ii) r in range 0.9 (Ω) to 2.0 (Ω) 1 2(f) obtain more values at other potential differences 1 start V axis at 3.0 (V) to expand scale 1

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3 A student investigates the refraction of light by a transparent block. He uses his results to determine a quantity known as the refractive index of the material of the block. The student’s ray-trace sheet is shown full size in Fig. 3.1. E P1 P2 N A B D C P4 P6 P5 P3 Fig. 3.1 (a) The student places a transparent block ABCD near the centre of the ray-trace sheet, as indicated in Fig. 3.1. (i) Draw a normal at point N, extending above AB. Label the upper end of the normal with the letter L. Extend the normal downwards until it crosses line CD. Label the point at which it crosses CD with the letter F. [1] (ii) The student draws line EN as shown in Fig. 3.1. On Fig. 3.1, measure the angle θ1 between the lines LN and EN. θ1 = ..................................................... [1] (b) The student places two pins, P1 and P2, on line EN, as shown in Fig. 3.1. Suggest whether the two pins are a suitable distance apart for accurate ray tracing. Explain your answer. statement .................................................................................................................................. explanation ............................................................................................................................... ................................................................................................................................................... [1] (c) The student views the images of P1 and P2 through the block. He places two pins, P3 and P4, so that pins P3 and P4, and the images of P1 and P2, all appear exactly one behind the other. • Draw a line through P3 and P4, extending the line until it meets NF. • Label the point at which this line meets NF with the letter G. • Label the point at which this line crosses CD with the letter H. • Draw a line joining points N and H. [1] (d) (i) Measure the length a of line NH. a = ......................................................cm Measure the length b of line GH. b = ......................................................cm [1] a (ii) Calculate a value n for the refractive index, using the equation n = . b n = ..................................................... [2] (e) The student repeats the above procedure for an angle θ2 = 40°. He places two pins, P5 and P6, so that pins P5 and P6, and the images of P1 and P2, all appear exactly one behind the other. • Draw a line through pins P5 and P6. Extend the line until it meets GH. • Label the point at which this line meets GH with the letter K. • Label the point at which this line crosses CD with the letter R. (i) Measure the angle α, where α is the smaller angle between lines RK and GH. α = ..................................................... [1] (ii) A student suggests that the angle α should be equal to the difference between the angle θ2 from (e) and the angle θ1 from (a)(ii). State whether your results support this suggestion. Justify your answer by reference to your results. statement .......................................................................................................................... justification ........................................................................................................................ ........................................................................................................................................... [1] (f) Suggest a precaution which should be taken to ensure accurate results in this type of experiment. ................................................................................................................................................... ............................................................................................................................................. [1] (g) Suggest why different students, all carrying out this experiment carefully, may not obtain identical results. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 11]

Mark scheme: 3(a)(i) normal correct 1 3(a)(ii) θ = 20° ± 1° 1 3(b) not suitable should be as far apart as possible 1 3(c) all lines present and neat 1 3(d)(i) a = 6.2 (cm) and b = 4.3 (cm) both ± 1 mm 1 3(d)(ii) n = 1.4(1) 1 expressed to 2/3 significant figures and no unit 1 3(e)(i) α = 21° ± 2° 1 3(e)(ii) statement matching results and justification matching statement (‘within limits of experimental accuracy’ / owtte) 1 3(f) any suitable precaution e.g. look at base of pins/keep pins vertical use thin pins thin lines 1 3(g) any one of: difficult to align pins/place pins accurately pins (too) thick lines too thick 1

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4 A student investigates the factors affecting the deflection of a wooden strip clamped at one end. Plan an experiment which enables him to investigate how one factor affects the distance D that the free end of the wooden strip moves downwards when loads are placed on it. The apparatus available includes: a variety of wooden strips which can be clamped as shown in Fig. 4.1 a set of masses with a hanger. In your plan, you should: • list any additional apparatus needed • state the key variables to be kept constant • explain briefly how to carry out the experiment, including how D is to be measured and any precautions that must be taken to ensure reliable results • draw a table, 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. You may add to Fig. 4.1 or draw another diagram if it helps to explain your plan. clamp wooden strip bench D Fig. 4.1 .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. .................................................................................................................................................................. ............................................................................................................................................................ [7]

Mark scheme: 4 MP1 apparatus: rule or equivalent 1 MP2 method: identify independent variable detail of deflection measurement and how it is measured 1 MP3 repeat for new independent variable 1 MP4 control variable: any variable appropriate to independent variable e.g. width of strip if thickness is the factor 1 MP5 table: columns, with units, for independent variable, deflection 1 MP6 analysis: compare readings in the table to see if change in factor produces change in deflection plot line graph (with axes specified) 1 MP7 additional point (one from): at least 5 sets of data taken repeat each measurement and take average 2nd appropriate control variable stated repeat experiment for different variation (e.g. different mass if thickness is factor) use of fiducial aid 1

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