Cambridge IGCSE Physics 0625 — 2017 Oct/Nov Paper 6 · Variant 3

1 Some students are investigating how the use of a lid affects the rate of cooling of water in a beaker. They are using the apparatus shown in Fig. 1.1. thermometer beakers lid A B Fig. 1.1 • A student pours 100 cm3 of hot water into beaker A. • He records the temperature of the water in beaker A and immediately starts a stopclock. • The student records the temperature θ of the water every 30 s. His readings are shown in Table 1.1. • The student repeats the procedure for beaker B using 75 cm3 of hot water. (a) Complete the headings and the time column in Table 1.1. [2] Table 1.1 beaker A beaker B without a lid with a lid t / θ/ θ/ 80.0 81.0 77.0 79.0 74.5 77.5 72.5 76.0 70.5 75.0 69.0 74.0 68.0 73.5 (b) Describe two precautions which should be taken to ensure that the temperature readings are as accurate as possible in the experiment. 1 ................................................................................................................................................ ................................................................................................................................................... 2 ................................................................................................................................................ ................................................................................................................................................... [2] (c) (i) Write a conclusion, stating how the use of the lid affects the rate of cooling of the water. Justify your answer by reference to the results. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[2] (ii) Suggest one change to the apparatus or procedure to make the comparison a fairer test. Explain why the change makes the test fairer. change .............................................................................................................................. ........................................................................................................................................... explanation ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [2] (iii) The temperature of the water in each beaker decreases. Describe one other similarity in the pattern of cooling in beakers A and B. ........................................................................................................................................... .......................................................................................................................................[1] (d) –10 0 10 20 30 40 50 60 70 80 90 100 110 °C Fig. 1.2 (i) Record the room temperature θR, shown on the thermometer in Fig. 1.2. θR = .......................................................... [1] (ii) Another student is carrying out the same experiment in a room with a room temperature that is much higher than θR. Suggest whether this might affect the cooling of the water in beaker A in her experiment. Briefly explain your answer. suggestion ......................................................................................................................... explanation ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [1] [Total: 11]

Mark scheme: 1(a) units ALL correct (symbols or words) 1 t values all present (0, 30, 60, 90, 120, 150 and 180) 1 1(b) two appropriate precautions, e.g.: avoidance of parallax(only if explained), wait until reading stops rising at start, ensure thermometer not touching beaker 2 1(c)(i) conclusion matching results 1 correct mention of comparative temperature change over 180 s 1 1(c)(ii) any suitable improvement relating to comparison: e.g. same volume of water, same initial temperature, insulate sides, use plastic beaker, stand on mat, use a thicker / more insulated lid, 1 matching explanation: e.g. lid only factor changed, cooling more rapid for higher temperatures, cooling different for different volumes, thermal energy only escapes from surface, less transfer of thermal energy by sides, effect of lid more marked 1 1(c)(iii) any appropriate similarity: e.g. both cool more rapidly at the start 1 1(d)(i) 23 (°C) 1 1(d)(ii) any suitable suggestion with a valid explanation greater temperature at end as cannot fall below room temperature, lower rate of cooling as temperature difference between water and room is smaller 1

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2 A student is investigating a circuit containing resistors. She is using the circuit shown in Fig. 2.1. power supply A X Y Fig. 2.1 (a) On Fig. 2.1, show a voltmeter connected so that it measures the potential difference across resistor X. [1] (b) The student uses the ammeter to measure the current IS in the circuit. 0.4 0.6 0.2 0.8 0 1.0 A Fig. 2.2 Record the current IS, as shown on the ammeter in Fig. 2.2. IS = ...........................................................[1] (c) (i) The student uses the voltmeter to measure the potential difference VX across resistor X and then reconnects it to measure the potential difference VY across resistor Y. 2 3 2 3 1 4 1 4 0 5 0 5 V V Fig. 2.3 Fig. 2.4 • Record the value of the potential difference VX across resistor X, shown in Fig. 2.3. VX = ............................................................... • Record the value of the potential difference VY across resistor Y, shown in Fig. 2.4. VY = ............................................................... [1] (ii) She then measures the potential difference VS across the combination of both resistors. 2 3 1 4 0 5 V Fig. 2.5 Record the value of the potential difference VS across the combination of both resistors, shown in Fig. 2.5. VS = ...........................................................[1] (iii) A student suggests that VS should be equal to (VX + VY). State whether the readings support this suggestion. Justify your statement with reference to the results. statement .......................................................................................................................... justification ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [2] (d) Calculate the resistance RS of the combination of resistors, using the readings from (b) and (c)(ii) and the equation VS RS = . IS RS = ...........................................................[2] (e) (i) The circuit components are to be rearranged so that: • resistors X and Y are in parallel • the ammeter will measure the total current in the circuit • the voltmeter will measure the potential difference across both resistors. In the space below, draw a diagram of this circuit using standard electrical symbols. [2] (ii) The student sets up the circuit as described in (e)(i). She measures and records the total current IP in the circuit and the potential difference VP across the resistors. IP = A VP = V The resistance of two resistors connected in parallel is less than the resistance of the same two resistors connected in series. State whether the readings indicate that she has set up the circuit correctly. Explain your answer. suggestion ......................................................................................................................... explanation ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [1] [Total: 11]

Mark scheme: 2(a) correct voltmeter symbol in parallel with X 1 2(b) IS = 0.18 (A) 1 2(c)(i) VX = 1.2 (V) AND VY = 2.3 (V) 1 2(c)(ii) correct units (A, V) seen in (b) and (c) 1 2(c)(iii) statement matching readings 1 justification, with use of values seen, matching readings and statement e.g: ‘3.5 V and 3.7 V are within limits of expt accuracy’ 1 2(d) correct calculation of Rs (20.6) 1 2 / 3 sig figs and unit(Ω) 1 2(e)(i) resistors in parallel with correct symbol 1 rest of circuit correct 1 2(e)(ii) valid suggestion AND explanation consistent with results 1

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3 Some students are determining the weight of a metre rule. They use the apparatus shown in Fig. 3.1. clamp forcemeter metre rule clamp 100.0 cm mark 0.0 cm mark d 200 g mass bench Fig. 3.1 (a) (i) The students suspend a 200 g mass at a distance d from the end of the rule. They then adjust the height of the clamp holding the forcemeter so that the rule is horizontal. Fig. 3.2 shows the forcemeter when the value of d is 10.0 cm. N 0.0 0.5 1.0 1.5 2.0 2.5 metre rule Fig. 3.2 In Table 3.1, record the forcemeter reading F, as shown in Fig. 3.2. [1] Table 3.1 d / cm F / N 10.0 30.0 1.05 50.0 1.65 70.0 1.95 90.0 2.25 (ii) The students repeat the procedure for values of d = 30.0 cm, 50.0 cm, 70.0 cm and 90.0 cm. Their readings are shown in Table 3.1. Explain how the students could make sure that the rule is horizontal before each reading. You may draw a diagram. ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[1] (b) Plot a graph of F / N (y-axis) against d / cm (x-axis). Start your axes from the origin (0, 0). Draw a best-fit line. [4] (c) (i) From your graph, determine F0, the value of F when d = 0.0 cm. F0 = ...........................................................[1] (ii) Calculate the weight WR of the metre rule, using the equation WR = 2 × F0. Give WR to a suitable number of significant figures for this experiment. WR = ...........................................................[2] (d) A student correctly plots your data points on another sheet of graph paper. State and explain whether his best-fit line is likely to be the same as yours. Justify your answer with reference to the plots. statement .................................................................................................................................. explanation ............................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... [1] (e) Another student, carrying out the same experiment, is not sure if some of his values of F are correct. Suggest one improvement to the procedure which would help him to obtain more reliable F values. ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[1] [Total: 11]

Mark scheme: 3(a)(i) F = 0.75 1 3(a)(ii) any reliable method e.g. equal distances between rule and bench in at least two places, line up with named horizontal surface, use of set-square between stand and rule 1 3(b) graph: axes labelled with quantity and unit 1 appropriate scales (plots occupying at least ½ grid and scales starting at 0,0) 1 plots all correct to ½ small square AND precise plots 1 Well-judged line AND thin line 1 3(c)(i) F0 correct from graph 1 3(c)(ii) WR in range 0.90 to 1.4 1 2 / 3 sig figs and unit (N) 1 3(d) statement matching plotted points AND explanation referring to line and scatter of data 1 3(e) repeat all readings and take average 1

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4 A student has a box of converging lenses but does not know their focal lengths. Plan an experiment which will enable her to determine an accurate value for the focal length f of one of the lenses, using the equation uv f = (u + v ) where u is the distance between an object and the lens and v is the distance between the lens and the focused image of the object. The apparatus available includes: a lens holder a 12 V lamp in a holder, with a power supply a card with a triangular hole covered with tracing paper. Write a plan for the experiment. You should: • list any additional apparatus needed • draw a diagram of how the apparatus will be arranged, clearly labelling u and v • write a method for carrying out the experiment including how f will be determined • state the precautions which should be taken to obtain a clear, focused image • state the precautions which should be taken to ensure that measurements are accurate once a focused image has been obtained. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ......................................................................................................................................................[7] [Total: 7]

Mark scheme: 4 MP1 additional apparatus: screen AND (metre) rule 1 MP2 diagram: suitable arrangement of apparatus with u & v labelled correctly 1 MP3 method: obtain (clear focused) image AND measure u, v 1 MP4 repeat for other values of u 1 MP5 one precaution for clear, focused image: move screen slowly / backwards and forwards, object AND lens AND screen perpendicular to bench / vertical, object and lens at same height (from bench), use of dark room / bright light 1 MP6 one precaution with measurements: clamp rule / fix to bench, mark centre of lens on holder avoidance of parallax explained and specific 1 MP7 one additional point: additional precaution, calculate f from given equation at least 3 values obtained, calculate average, mention of at least one appropriate u value, mention of preliminary expt to obtain rough f value (e.g. light from window) 1

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