Cambridge IGCSE Physics 0625 — 2015 Feb/March Paper 6 · Variant 2

1 A student is determining the mass of a metre rule by a balancing method. He is using the apparatus shown in Fig. 1.1. mass M metre rule a b 50.0 cm mark pivot 95.0 cm mark Fig. 1.1 (a) He places the metre rule on the pivot and then places a mass M = 20 g with its centre at the 95.0 cm mark. Suggest how he could ensure that the mass is placed accurately at the 95.0 cm mark. You may draw a diagram. ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[1] (b) Keeping the mass at the 95.0 cm mark, he adjusts the position of the metre rule on the pivot until the metre rule is as near to being balanced as possible. The student then determines the distance a between the 50.0 cm mark and the pivot and the distance b between the 95.0 cm mark and the pivot. He repeats the procedure for values of M = 40 g, 60 g, 80 g and 100 g. His results are shown in Table 1.1. Table 1.1 M / g a / cm b / cm S 20 6.5 38.5 40 11.2 33.8 60 15.2 29.8 80 17.1 27.9 100 20.0 25.0 a For each value of M, calculate and record in the table the value S, where S = b. [1] (c) Plot a graph of S (y-axis) against M / g (x-axis). [4] (d) (i) Determine the gradient G of the graph. Show clearly on the graph how you obtained the necessary information. G = ...........................................................[1] 1 (ii) The mass MR of the metre rule is numerically equal to G. Write down a value for MR to a suitable number of significant figures for this experiment. MR = ........................................................g [1] (e) Determination of MR by this method relies on the centre of mass of the rule being at the 50.0 cm mark. Suggest how you could use the apparatus to test whether this is the case. You may draw a diagram. ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[1] [Total: 9]

Mark scheme: 1 (a) measure ½ mass length either side of 95.0 cm OR mark side of mass AND rule [1] (b) correct calculations of S, rounding to 0.17, 0.33, 0.51, 0.61, 0.80 [1] (c) axes labelled with quantity and unit [1] appropriate scales [1] plots correct to ½ small square [1] well-judged straight line, thin line, precise plots [1] (d) (i) G present AND triangle method seen on graph [1] (ii) MR = in range 113 to 140 g AND to 2/3 sig. fig. [1] (e) see if rule balances when pivot at 50 cm mark owtte [1] [Total: 9]

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2 The class is investigating whether the insulation around a container affects the rate at which water cools. Two test-tubes are set up as shown in Fig. 2.1. thermometers A B Fig. 2.1 Test-tube A has one layer of insulation. Test-tube B has three layers of insulation. This is indicated by the cross-sections of the test-tubes shown in Fig. 2.2. overlap fixed by tape three layers one layer of of insulation insulation test-tube A test-tube B Fig. 2.2 (a) The students pour hot water into each test-tube, up to the level of the top of the insulation. They record, in Table 2.1, the temperatures θ of the water in each test-tube and immediately start a stopclock. They also record the temperatures θ at times t = 30 s, 60 s, 90 s, 120 s,150 s and 180 s. Complete the table. Table 2.1 test-tube A test-tube B (1 layer) (3 layers) t / θ/ θ/ 71.0 75.5 68.5 73.5 66.0 71.0 64.0 69.5 62.0 67.5 60.5 66.0 58.5 64.5 [2] (b) From the results in the table, state how increasing the number of layers of insulation affects the rate at which water cools. Justify your answer by referring to the results. statement .................................................................................................................................. ................................................................................................................................................... justification ................................................................................................................................ ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... [2] (c) State two ways in which the temperature readings in this experiment could be made as reliable as possible. 1. ............................................................................................................................................... ................................................................................................................................................... 2. ............................................................................................................................................... ................................................................................................................................................... [2] (d) Suggest two improvements to the apparatus or procedures which will ensure that the investigation into the effect of insulation on the rate of cooling is more reliable. 1. ............................................................................................................................................... ................................................................................................................................................... 2. ............................................................................................................................................... ................................................................................................................................................... [2] [Total: 8]

Mark scheme: 2 (a) units correct, accept symbols or words [1] t values correct: 0, 30, 60, 90, 120, 150, 180 [1] (b) statement matching results with comparison of temperature changes over [1] whole available range OR for 120 s from 71 °C justification with mention of ‘in the same time’ owtte [1] (c) two precautions relating to temperature measurement,e.g. [2] • thermometer at same depth • read thermometer with reading at eye level/90° to scale/explain parallax • wait until thermometer has stopped rising (at the start) (d) two improvements to apparatus or procedure, e.g. [2] • insulation all way up side of test-tube/covering bottom of test-tube • start taking measurements at same temperature/same initial temp. of water • same volume of water/use measuring cylinder for water • plot cooling curves • use metal/thinner glass test-tubes • more layers of insulation • make sure insulation is dry • avoid overlapping insulation • use same tube/same tube thickness in each experiment [Total: 8]

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3 Some students are investigating the link between the brightness of a filament lamp and its resistance. The circuit is shown in Fig. 3.1. power supply 3 V metre rule l resistance wire 0.0 cm mark A crocodile clip Fig. 3.1 (a) On Fig. 3.1, use standard symbols to show a voltmeter connected to measure the potential difference across the lamp. [1] (b) The students attach the crocodile clip to various lengths l of the resistance wire and record, in Table 3.1, the potential difference V and the current I for the lamp. They also record observations of the lamp filament. Table 3.1 observation of l / cm V / V I / A R / Ω lamp filament 100 2.5 0.26 bright 60 1.5 0.19 dim 20 0.5 0.11 just glowing Voltmeters with the ranges shown in Fig. 3.2 are available. 0.8 1.0 1.2 0.6 2 3 0.4 1.41.6 1 4 0.2 1.8 0 2.0 0 5 V V 4 5 6 3 7 2 8 1 9 0 10 V Fig. 3.2 (i) On Fig. 3.2, circle the voltmeter which is most appropriate for this experiment. (ii) Draw an arrow on this voltmeter to show the reading when the crocodile clip is attached to a length l = 60 cm of the resistance wire. [2] (c) Calculate, and record in the table, the resistance R of the lamp for each value of l, using the V equation R = . [2] I (d) From the results and the observations of the lamp filament, state the link, if any, between the brightness of the lamp and its resistance. Explain clearly how the results support your statement. statement .................................................................................................................................. explanation ............................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... [2] (e) A student wishes to see if another lamp shows the same link between brightness and resistance. However, his lamp only glows dimly when a potential difference of 3 V is applied across it. The student decides that a method using a resistance wire is not suitable. Suggest an alternative circuit and apparatus which would allow him to vary the brightness of his lamp and measure the potential difference and current for his lamp. You may draw a circuit diagram. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[3] [Total: 10]

Mark scheme: 3 (a) correct voltmeter symbol with appropriate parallel connection [1] (b) (i) meter with 5 V range circled [1] (ii) arrow indicating 1.5 V on circled meter [1] (c) R calculations correct (9.6 or 9.62, 7.9 or 7.89, 4.5 or 4.55) [1] consistent 2 or consistent 3 sig. figs. [1] note: allow 1 sig. fig. fewer for l = 20 cm (d) link consistent with results [1] figures to support, matching statement – at least two R values compared [1] (e) increased supply voltage [1] use of variable resistor OR variable voltage supply clearly indicated as such [1] any other suitable point, e.g. [1] • voltmeter with larger range • ammeter with larger range • variable resistor symbol and connection correctly shown [Total: 10]

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4 A student is carrying out an experiment with a small converging lens. The student sets up the apparatus as shown in Fig. 4.1. The distances are shown full size. illuminated screen object u1 v1 lens Fig. 4.1 (a) She moves the screen until a sharp image of the illuminated object appears on the screen. (i) Using Fig. 4.1, measure and record the distance u1 between the illuminated object and the lens, and the distance v1 between the lens and the screen. u1 = ............................................................... v1 = ............................................................... [2] (ii) Calculate a value for the focal length f of the lens, using your results from (a)(i) and the u1v1 equation f = . (u1 + v1) f = ...........................................................[2] (b) Keeping the illuminated object and screen in the same positions, she moves the lens towards the screen until a second sharp image is seen on the screen. The distances are shown full size. illuminated screen object u2 lens Fig. 4.2 (i) Using Fig. 4.2, measure and record the new distance u2 between the illuminated object and the lens. u2 = ............................................................... (ii) The student suggests that u2 and v1 should be equal. State whether the lens positions obtained by the student support this suggestion. Justify your statement by reference to the results. statement .......................................................................................................................... justification ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [2] (c) Describe two precautions that should be taken in order to obtain reliable results in this type of experiment. 1. ............................................................................................................................................... ................................................................................................................................................... 2. ............................................................................................................................................... ................................................................................................................................................... [2] [Total: 8]

Mark scheme: 4 (a) (i) u1 = 5.0(cm)/50(mm) [1] v1 = 8.7(cm)/87(mm) [1] (ii) correct calculation of f, expect 3.1 to 3.2 (cm)/31 to 32 (mm), e.c.f.(a)(i) [1] matching unit [1] (b) u2 in range 8.8 to 8.9(cm)/88 to 89(mm) AND statement matching results [1] appropriate justification e.g. within limits of experimental accuracy owtte [1] (c) two appropriate precautions, e.g. [2] • carry out experiment in dark room/no direct (sun)light/bright lamp • lens and object same height above bench • lens, object and screen vertical • move screen/lens back and forth/slowly to obtain sharp image • fix/place rule on bench • mark centre of lens on holder • readings repeated [Total: 8]

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5 Two students are investigating thermal energy transfer. They are using the apparatus shown in Fig. 5.1. °C °C 110 110 100 100 90 90 80 80 70 70 60 60 50 50 40 40 30 30 iron block 20 20 10 10 0 0 –10 –10 beaker A beaker B Fig. 5.1 Beaker A contains hot water and beaker B contains cold water at room temperature. (a) Record the temperature θH of the hot water and the temperature θC of the cold water as shown on the thermometers in Fig. 5.1. θH = ............................................................... θC = ............................................................... [1] (b) Using metal tongs, one of the students places the iron block in the hot water in beaker A for 30 seconds. He then removes the block and places it in the cold water in beaker B. The other student then measures the temperature of the water in beaker B and finds that it has risen to 35 °C. Their teacher suggests that this value is lower than expected. (i) The students suggest that, immediately before the iron block was put into the cold water, the temperature of the iron block was not the same as θH. Suggest one reason for this and a possible improvement to the experiment which could make the temperature of the block nearer to θH. reason ............................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... improvement ...................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... [2] (ii) The students also think that, when the block cooled in the water, not all of the thermal energy lost by the block raised the temperature of the water. Suggest one reason for this and a possible improvement to the experiment which would reduce thermal losses. reason ............................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... improvement ...................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... [2] [Total: 5]

Mark scheme: 5 (a) θ H = 74 AND θ C = 23(°C) [1] (b) (i) suitable reason, e.g. [1] • temperature not able to reach max θ H (in 30s) • temperature dropped on transfer • conduction/transfer to metal tongs matching improvement, e.g. [1] • leave block in hot water longer • transfer more quickly • use insulated tongs/cotton round block (ii) suitable reason, e.g. [1] • some (thermal) energy transferred to beaker, • some (thermal) energy transferred to surroundings, • evaporation/convection (into atmosphere) matching improvement, e.g. [1] • use a less conducting material for beaker/owtte • insulate beaker • allow for beaker in any calculation • lid on beaker [Total: 5]

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