Cambridge IGCSE Physics 0625 — 2019 Oct/Nov Paper 6 · Variant 3

1 A student investigates how the resistance of a filament lamp changes with the potential difference (p.d.) across it. He uses the circuit shown in Fig. 1.1. power supply slide wire l lamp crocodile clip A Fig. 1.1 (a) On Fig. 1.1, draw the symbol for a voltmeter connected to measure the potential difference across the lamp. [1] (b) The student connects the crocodile clip to a length l = 20.0 cm of the slide wire. He measures the potential difference V and the current I for the lamp. (i) Record the voltmeter and ammeter readings shown in Fig. 1.2 for a value of l = 20.0 cm. V = ............................................................... I = ............................................................... [1] 2 3 0.4 0.6 1 4 0.2 0.8 0 5 0 1.0 V A Fig. 1.2 (ii) Calculate, and record in Table 1.1, the resistance R of the lamp at l = 20.0 cm. V Use your readings from (b)(i) and the equation R = . [1] I Table 1.1 l / cm R / Ω 20.0 40.0 7.5 60.0 10 80.0 12 100.0 13 (c) The student connects the crocodile clip to other lengths l of the slide wire. He measures the potential difference V and the current I for the lamp and calculates the resistance each time. His results are shown in Table 1.1. Plot a graph of R / Ω (y-axis) against l / cm (x-axis). [4] (d) The student notices that the lamp is very dim when l = 20.0 cm but becomes very bright when l = 100.0 cm. State what the shape of the graph tells you about how the resistance of the lamp changes with the temperature of the filament. Justify your statement using your results from the graph. statement .................................................................................................................................. justification ................................................................................................................................ ................................................................................................................................................... [2] (e) In this type of experiment, it is possible to change the current in the lamp by using a variable resistor instead of a slide wire. On Fig. 1.3, complete the circuit diagram to show a variable resistor used for this purpose. power supply A Fig. 1.3 [2] [Total: 11]

Mark scheme: 1(a) correct voltmeter symbol in parallel with lamp 1 1(b)(i) V = 0.6(V) and I = 0.14(A) 1 1(b)(ii) R = 4.3(Ω) 1 1(c) graph: axes labelled correct orientation, with quantity and unit 1 appropriate scales (plots occupying at least ½ grid) 1 plots all correct to less than ½ small square and precise plots 1 well-judged line and thin line 1 1(d) resistance increases as temperature increases 1 temperature / resistance increases with length 1 1(e) variable resistor symbol correct (rectangle with strike-through arrow only) 1 in series and rest of circuit correct 1

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2 Some students determine the focal length of a converging lens by two different methods. They use the apparatus shown in Fig. 2.1. screen illuminated triangle u v lens bench Fig. 2.1 (a) A student sets the distance U between the illuminated triangle and the lens. She moves the screen until a sharp image of the triangle is seen on the screen. Method 1 (i) On Fig. 2.1, measure the distance u between the illuminated triangle and the lens. u = ............................................................... On Fig. 2.1, measure the distance v between the lens and the screen. v = ............................................................... [1] (ii) Fig. 2.1 is drawn to 1/5th scale. Calculate the actual distance U between the illuminated triangle and the lens in the experiment. U = ............................................................... Calculate the actual distance V between the lens and the screen in the experiment. V = ............................................................... [1] UV (iii) Calculate a value f1 for the focal length of the lens, using the equation f1 = . (U + V) f1 = ......................................................... [1] (iv) Briefly describe a technique to obtain an image on the screen that is as sharp as possible in this experiment. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] Method 2 (b) (i) On Fig. 2.2, measure hO, the height of the illuminated triangle. hO = ............................................................... On Fig. 2.3, measure hI, the height of the image on the screen. hI = ............................................................... [1] hI hO Fig. 2.2 Fig. 2.3 hI (ii) Calculate a value for the magnification M, using the equation M = . hO M = ......................................................... [1] V (iii) Calculate a second value f2 for the focal length of the lens, using the equation f2 = (M + 1) and the value of V from (a)(ii). f2 = ......................................................... [1] (c) A student suggests that f1 and f2 should be equal. State whether the results support this suggestion. Justify your statement with reference to the results. statement .................................................................................................................................. justification ................................................................................................................................ ................................................................................................................................................... [2] (d) State one precaution that could be taken to ensure that the measurements in the experiment are taken as reliably as possible. ................................................................................................................................................... ............................................................................................................................................. [1] (e) Suggest which of Method 1 or Method 2 is likely to give the more accurate value for the focal length. Explain the reason for your choice. suggestion ................................................................................................................................ explanation ............................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... [1] [Total: 11]

Mark scheme: 2(a)(i) u = 5.0(cm) and v = 7.6(cm) 1 2(a)(ii) U = 25(.0)(cm) and V = 38(.0)(cm) 1 2(a)(iii) f1 15(.1)(cm) and 2/3 sig fig and unit 1 2(a)(iv) move screen slowly / backwards and forwards 1 2(b)(i) hO = 1.5(cm) and hI = 2.4(cm) 1 2(b)(ii) M = 1.6 and no unit 1 2(b)(iii) f2 = 15 / 14.6(cm) 1 2(c) statement matching results 1 values within limits of experimental accuracy / owtte 1 2(d) any one from: • mark position of lens on holder ; • clamp rule / place rule on bench ; • ensure screen, lens and object all perpendicular (to bench) / vertical ; • view scale perpendicularly ; • mark top and bottom of image and measure later 1 2(e) either method suggested if matching valid explanation e.g. METHOD 1: difficult to measure height of image in method 2 METHOD 1: smaller lengths measured in method 2 / reverse argument METHOD 2: can’t measure u and v to lens accurately in method 1 1

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3 The class is investigating the behaviour of a spring, and then using the spring to determine the weight of an object. The apparatus is shown in Fig. 3.1. clamp spring l load Fig. 3.1 (a) The stretched length l of the spring, indicated in Fig. 3.1, is to be measured. Describe two precautions that could be taken when measuring the length of the stationary spring, to ensure an accurate reading. You may draw a diagram. 1 ............................................................................................................................................... ................................................................................................................................................... 2 ............................................................................................................................................... ................................................................................................................................................... [2] (b) • A student measures the length l0 of the spring without any load. l0 = ..........................................................cm2.1 • Various loads L are hung on the spring. The stretched length l of the spring for each load is recorded in Table 3.1. Table 3.1 L / N l / cm e / cm 1.0 6.3 2.0 10.5 3.0 14.7 • Calculate, and record in Table 3.1, the extension e of the spring for each load L. Use the equation e = (l – l0). [1] (c) The loads are removed and an object X is suspended from the spring. lX object X Fig. 3.2 (i) Measure the stretched length lX of the spring on Fig. 3.2. lX = .................................................... cm [1] (ii) Estimate the weight WX of object X. Explain how you obtained your answer. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... WX = ........................................................... N [2] (d) A student measures the weight of a different load using a similar method. He gives the weight as 4.532 N. Explain why this is not a suitable number of significant figures for this experiment. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [1] (e) (i) Another student suggests that e is directly proportional to L. State whether the results support her suggestion. Use values from the results in Table 3.1 to justify your statement. statement .......................................................................................................................... justification ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [2] (ii) The student wishes to plot a graph of L against e to test if the two quantities are directly proportional. State how her graph line could show that e is directly proportional to L. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] [Total: 11]

Mark scheme: 3(a) any two from: • rule close / parallel to spring ; • eye perpendicular to reading / use set square ; • clamp rule 2 3(b) correct calculations of e (4.2, 8.4, 12.6) 1 3(c)(i) lx = 11.4(cm) 1 3(c)(ii) 2.0 N < Wx < 2.5(N) 1 working showing use of ratio/correct logic 1 3(d) data only given to 1 dp / 2 or 3 sig fig 1 3(e)(i) statement matching results 1 correct justification matching statement e.g. • L/e constant • e doubles when L doubles 1 3(e)(ii) straight line 1 (line) through origin 1

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4 A student is investigating ways of slowing the rate of cooling of hot liquids in a container. The student knows that a lid will reduce the rate of cooling. He wants to find out if the thickness of the lid makes any difference to the rate of cooling. Plan an experiment which will enable him to compare the effects of lids of different thicknesses. In your plan, you should: • list the apparatus needed • explain briefly how you would carry out the investigation, including the measurements to be taken • state any key variables that would need to be kept the same • draw a suitable table or tables, with column headings, to show how the readings would be displayed (you are not required to enter any readings in the table) • explain how you would use your readings to reach a conclusion. You may draw a diagram if it helps to explain your plan. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7] [Total: 7]

Mark scheme: 4 MP1 Apparatus beaker and (material for) lid and thermometer and stop clock (or alternative) 1 MP2 Method pour (hot) water into container measure temperature of (hot) water over period of time 1 MP3 Method repeat for different thicknesses of lid 1 MP4 & MP5 Control variables any two from: • same initial/starting temperature of water ; • same volume of water ; • same size / material / thickness of beaker ; • same material for lid ; • same time for measuring temperature change / same temperature difference for measuring time taken • same room temperature / other environmental condition 2 MP6 Table suitable column headings and units 1 MP7 Analysis any one from: • comparison of temperature decrease / rates of cooling with thickness / different lids • draw a suitable graph with axes stated 1

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