Cambridge IGCSE Physics 0625 — 2018 May/June Paper 6 · Variant 3

1 A student is investigating how partly covering the surface of the water in a beaker affects the rate at which the water cools. The apparatus used is shown in Fig. 1.1. thermometer lid water Fig. 1.1 (a) –10 0 10 20 30 40 50 60 70 80 90 100 110 °C Fig. 1.2 Record the room temperature θR, shown on the thermometer in Fig. 1.2. θR = ......................................................... [1] (b) The student pours 100 cm3 of hot water into a beaker. She places lid A on the beaker. This leaves half of the water surface uncovered, as shown in Fig. 1.3. She records the temperature of the water in the beaker and immediately starts a stopclock. She records the temperature θ of the water every 30 s. Her readings are shown in Table 1.1. She repeats the procedure using lid B. This leaves a quarter of the water surface uncovered, as shown in Fig. 1.4. beaker lid A beaker lid B uncovered area uncovered area Fig. 1.3 Fig. 1.4 Complete the headings and the time t column in Table 1.1. [2] Table 1.1 beaker with lid A beaker with lid B t / θ / θ / 0 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 (c) Describe a precaution that should be taken to ensure that the temperature readings are as accurate as possible in the experiment. ................................................................................................................................................... .............................................................................................................................................. [1] (d) (i) Write a conclusion to this experiment, stating for which lid the rate of cooling is greater. Explain your answer by reference to the results. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [2] (ii) Suggest a change to the apparatus that could produce a greater difference between the rates of cooling for lid A and lid B. Explain why the change might produce a greater difference. change .............................................................................................................................. ........................................................................................................................................... explanation ........................................................................................................................ ........................................................................................................................................... [2] (e) A student suggests that the rate of cooling is directly proportional to the percentage of the uncovered surface area. He wants to draw a graph of cooling rate against the percentage of uncovered area to investigate this. Describe how his graph line will show whether the rate of cooling and the percentage of uncovered surface area are directly proportional. ................................................................................................................................................... .............................................................................................................................................. [2] (f) Students in other countries carry out the same experiment. Suggest one factor that they should keep the same if they are to obtain similar readings. ................................................................................................................................................... .............................................................................................................................................. [1] [Total: 11]

Mark scheme: 1(a) 21(.0) (ºC) 1 1(b) s, ºC, ºC all correct 1 30, 60, 90, 120, 150, 180 1 1(c) appropriate precaution e.g. avoidance of parallax (only if explained) / wait until reading stops rising (at start) 1 1(d)(i) beaker with lid A (has a greater rate of cooling) 1 correct mention of comparative temperature change over 0 to 180 s 1 1(d)(ii) any suitable change to apparatus relating to comparison e.g. insulate sides / stand on mat use plastic beaker thicker lid use of fan use wider beaker 1 matching explanation e.g. thermal energy only escapes from surface less transfer of thermal energy by sides / bottom less conduction through lid larger surface area (for evaporation to occur) 1 1(e) straight line 1 through the origin 1 1(f) any appropriate factor e.g. volume of water initial temperature of water (same) lids type / material / size of beaker room temperature / appropriate environmental factor

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2 A student is investigating a circuit containing resistors. He is using the circuit shown in Fig. 2.1. Resistor X has a resistance R = 1 Ω. power supply A X Fig. 2.1 (a) On Fig. 2.1, draw a voltmeter connected so that it measures the potential difference (p.d.) across resistor X. [1] (b) The student uses the ammeter to measure the current in the circuit and uses the voltmeter to measure the potential difference (p.d.) across resistor X. The readings are shown in Fig. 2.2 and Fig. 2.3. 0.4 0.6 2 3 0.2 0.8 1 4 0 1.0 0 5 A V Fig. 2.2 Fig. 2.3 (i) The student repeats the procedure using resistors Y and Z. His readings are shown in Table 2.1. Record, in Table 2.1, the value of the current I in the circuit and the value of the potential difference (p.d.) V across resistor X shown in Fig. 2.2 and Fig. 2.3. Table 2.1 resistor R / I / V / X 1 Y 3 0.55 1.7 Z 10 0.24 2.4 [2] (ii) Add units to the column headings in Table 2.1. [2] (c) Calculate the power P supplied to each of the resistors X, Y and Z. Use the readings from Table 2.1 and the equation P = I × V. Give your answers to a suitable number of significant figures. power P supplied to resistor X = ......................................................... W power P supplied to resistor Y = ......................................................... W power P supplied to resistor Z = ......................................................... W [2] (d) Describe how the value of the power P changes as R increases. ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [2] (e) Another student plans to investigate the relationship between P and R in more detail. Suggest two modifications to the procedure that will enable her to do this. 1. .............................................................................................................................................. ................................................................................................................................................... 2. .............................................................................................................................................. ................................................................................................................................................... [2] [Total: 11]

Mark scheme: 2(a) correct voltmeter symbol in parallel with X 1 2(b)(i) I = 0.86 (A) 1 V = 0.9 (V) 1 2(b)(ii) Ω 1 A, V 1 2(c) correct calculations of P (0.77 / ecf, 0.94, 0.58(W)) 1 consistent 2 or consistent 3 significant figures 1 2(d) increases (at first) 1 to a maximum AND then decreases 1 2(e) any 2 additions from: draw a graph; different / more resistors / values of resistance / greater range of values for resistance; use (at least) 5 sets of values for resistance 2

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3 A student is investigating the image produced by a converging lens. She is using the apparatus shown in Fig. 3.1. screen illuminated object u lens Fig. 3.1 (a) The illuminated object consists of a triangular-shaped hole in a piece of card. Fig. 3.2 shows, full size, the illuminated object. Measure and record the height ho of the triangular-shaped hole. ho = ................................................... cm [1] card ho Fig. 3.2 (b) The distance u between the triangular object and the centre of the lens is set to 20.0 cm. The screen is moved until a focused image of the illuminated object is seen, as shown in Fig. 3.3. screen hI Fig. 3.3 The student repeats the procedure for u values of 30.0 cm, 40.0 cm, 50.0 cm and 60.0 cm. Her results are shown in Table 3.1. (i) Measure and record in the first row of Table 3.1, the height hI of the image. [1] (ii) Calculate, and record in the table, a value N using your measurements for ho and hI and ho the equation N = . hI Table 3.1 u / cm hI / cm N 20.0 30.0 1.5 0.93 40.0 0.9 1.6 50.0 0.6 2.3 60.0 0.5 2.8 [1] (c) Plot a graph of u / cm (y-axis) against N (x-axis). You do not have to start your graph at the origin (0, 0). [4] (d) Determine the gradient G of the graph. Show clearly on the graph how you obtained the necessary information. G = ......................................................... [2] (e) Describe one difficulty that might be experienced when measuring the height of the image hI. Suggest an improvement to the apparatus to overcome this difficulty. difficulty ..................................................................................................................................... ................................................................................................................................................... improvement ............................................................................................................................. ................................................................................................................................................... [2] [Total: 11]

Mark scheme: 3(a) hO = 1.4 (cm) 1 3(b)(i) hI = 4.5 (cm) 1 3(b)(ii) N = 0.31 / ecf 1 3(c) graph: axes labelled correct orientation, with quantity and unit 1 appropriate scales (plots occupying at least ½ grid) 1 plots all correct to ½ small square and precise plots 1 well judged line and thin line 1 3(d) G in range 14.0 to 17.0 1 triangle method seen on graph occupying at least half line 1 3(e) any inherent difficulty e.g. hand / ruler in way of image OR screen can move (when measuring) 1 matching improvement to apparatus e.g. use translucent screen and view from behind OR fix ruler / grid to screen OR clamp screen in place 1

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4 A student is investigating the force needed to just slide a block across a surface. Plan an experiment that will enable him to investigate how the force needed varies with the mass of the block. The apparatus available includes: a light, flat wooden block with a hook fitted as shown in Fig. 4.1 a pulley which can be clamped to a bench. wooden block hook Fig. 4.1 In your plan, you should: • list any additional apparatus needed • draw a clearly labelled diagram of how the apparatus will be arranged • give brief instructions for carrying out the experiment • describe any precautions which should be taken to ensure reliable results • suggest a graph which could be drawn. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [7] [Total: 7]

Mark scheme: 4 Apparatus: forcemeter, (10 g and 100 g) masses / masses only (if clear they are used to change the mass of the block and as weights to the block via the pulley) 1 Diagram: block, workable means of pulling and measuring force 1 Method (2): measure force required to make block slide / find mass (on pulley) required to make block slide 1 repeat for new value of mass 1 Precautions: any one from: same surface to slide on / repeat each measurement and take average / same angle of pulling force 1 Graph: mass on block vs force (needed to slide) 1 Any additional point: at least 5 sets of data taken / keep force horizontal / add mass of block to load / extra precaution 1

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