Cambridge IGCSE Physics 0625 — 2021 Oct/Nov Paper 5 · Variant 3

1 In this experiment, you will investigate the effect of insulation on the cooling of water. Carry out the following instructions, referring to Fig. 1.1. Beaker A is covered with material that is a thermal insulator. Beaker B is identical to beaker A but has no insulation. thermometer lid beaker A beaker B bench insulation Fig. 1.1 (a) • Remove the lid from beaker A. • Pour 150 cm3 of hot water into beaker A and replace the lid. • Place the thermometer in the water in beaker A. In the first row of Table 1.1, record the temperature θ of the water at t = 0 and immediately start the stop-clock. Record, in Table 1.1, the temperature θ of the water at times t = 30 s, t = 60 s, t = 90 s, t = 120 s, t = 150 s and t = 180 s. [1] • Remove the thermometer from the beaker. (b) (i) Repeat (a) for beaker B. [2] (ii) Add units to the column headings in Table 1.1. [1] Table 1.1 beaker A beaker B with insulation without insulation t / θ/ θ/ 0 30 60 90 120 150 180 (c) Write a conclusion stating whether the insulation affects the rate of cooling of the water. Justify your answer by reference to values from your results. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (d) (i) Calculate the average cooling rate x1 during the first half of the experiment for the water in beaker B. Use your readings for beaker B from Table 1.1 and the equation θ0 – θ90 x1 = , T where T = 90 s and θ0 and θ90 are the temperatures of the water in beaker B at t = 0 and t = 90 s. Include the unit. x1 = .......................................................... [1] (ii) Calculate the average cooling rate x2 during the second half of the experiment for the water in beaker B. Use your readings for beaker B from Table 1.1 and the equation θ90 – θ180 x2 = , T where T = 90 s and θ90 and θ180 are the temperatures of the water in beaker B at t = 90 s and t = 180 s. Include the unit. x2 = .......................................................... [1] (e) (i) Suggest an additional experiment to test whether the lid affects the cooling rate of the water in beaker B. State how the readings are used to show the effect. You are not required to carry out this additional experiment. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (ii) A student suggests that the temperature of the water in beaker B at t = 0 for this additional experiment must be the same as in (b)(i) for the comparison to be fair. State whether your results support this suggestion. Use your results from (d) to explain whether this precaution is necessary. statement .......................................................................................................................... explanation ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [2] [Total: 11]

Mark scheme: 1(a) Θ to nearest °C for beaker A decreasing 1 1(b)(i) θ for beaker B decreasing and recorded to at least 1 °C 1 decreasing more quickly than A 1 1(b)(ii) s, °C both correct 1 1(c) statement matching readings in table 1 comparison of temperature changes over 180 s, matching statement (need to see values used in justification) 1 1(d)(i) correct calculation of x1 and unit °C / s (seen for x1 or x2 and not contradicted) 1 1(d)(ii) x2 < x1 1 1(e)(i) beaker B without lid and calculate cooling rate of beaker B (and compare / subtract) 1 1(e)(ii) statement matching results for beaker B with values quoted 1 justification matching statement 1

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2 In this experiment, you will compare the resistances of two wires. The circuit has been set up for you. Carry out the following instructions, referring to Fig. 2.1. V crocodile clip A resistance wire A l resistance wire B Fig. 2.1 (a) Connect the crocodile clip to a length l = 90.0 cm of resistance wire A. Close the switch. Measure, and record in Table 2.1, the value of potential difference (p.d.) V and current I for the wire. Open the switch. Calculate, and record in Table 2.1, the resistance R of 90.0 cm of wire A. Use your values of V and I and the equation V R = . I [3] Table 2.1 wire l / cm V / I / R / A 90.0 B 90.0 A 50.0 B 50.0 (b) (i) Repeat step (a) for l = 90.0 cm of wire B, l = 50.0 cm of wire A and l = 50.0 cm of wire B. [2] (ii) Complete the headings in Table 2.1. [1] (c) (i) Calculate a value P using your results from Table 2.1 and the equation R for 90.0 cm of wire A P = R for 90.0 cm of wire B. P = .......................................................... [1] (ii) Calculate a value Q using your results from Table 2.1 and the equation R for 50.0 cm of wire A Q = R for 50.0 cm of wire B. Q = .......................................................... [1] (iii) A student suggests that the values of P and Q should be equal. State whether your results support this suggestion. Justify your answer by reference to values from your results. statement .......................................................................................................................... justification ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [2] (d) Suggest one reason why students all doing this experiment carefully with the same apparatus may not obtain the same results. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 11]

Mark scheme: 2(a) V all < 3.0 V 1 I all < 1.00 A 1 All V to at least 1dp and all I to at least 2dp 1 2(b)(i) correct calculations of R 1 R consistent 2 or 3 significant figures 1 Question Answer Marks 2(b)(ii) V, A, Ω all correct 1 2(c)(i) P > 1 1 2(c)(ii) Q > 1 and within 10% of P 1 2(c)(iii) statement matching results and values used 1 justification matching statement e.g. within limits of experimental accuracy / owtte 1 2(d) valid inherent source of inaccuracy e.g: crocodile clip connection not even / difficult to connect at exactly the correct length / resistance wires not uniform 1

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3 In this experiment, you will investigate the image produced by a converging lens. Carry out the following instructions, referring to Fig. 3.1. triangular screenobject u lens hO bench Fig. 3.1 (a) Measure and record the height hO of the triangular object. hO = ........................................................... cm • Place the lens a distance u = 20.0 cm from the triangular object. • Place the screen close to the lens. • Switch on the lamp. • Move the screen away from the lens until a clear, focused image of the triangular object is seen on the screen. • Measure, and record in Table 3.1, the height hI of the image. Repeat the procedure for u = 25.0 cm, u = 30.0 cm, u = 35.0 cm and u = 40.0 cm. Switch off the lamp. Table 3.1 1 1 u / cm hI / cm  cm hI 20.0 25.0 30.0 35.0 40.0 [1] 1 (b) For each distance u, calculate, and record in Table 3.1, the value of . [1] hI 1 1(c) Plot a graph of u / cm (y-axis) against (x-axis). Start the axes at the origin (0,0).  cm hI [4] 1 (d) (i) From your graph, determine u0, the value of u when = 0.0. hI u0 = .......................................................... [1] (ii) Determine the gradient of the graph. Show clearly on the graph how you obtained the necessary information. gradient = .......................................................... [1] (iii) Calculate the focal length f of the lens. Use your value of hO from (a) and the equation G f = , hO where G is numerically equal to the gradient from (d)(ii). f = .......................................................... [1] (e) Describe one difficulty that can be experienced when measuring the height of the image. Suggest an improvement to overcome this difficulty. difficulty ..................................................................................................................................... ................................................................................................................................................... improvement ............................................................................................................................. ................................................................................................................................................... [2] [Total: 11]

Mark scheme: 3(a) 1 3(b) 1 / hI calculation correct 1 3(c) graph: • axes labelled with quantity and unit 1 • appropriate scales (plots occupying at least ½ grid) 1 • plots all correct to ½ small square, precise plots 1 • well judged and thin line 1 3(d)(i) u0 read correctly from graph and in range 13.0 (cm) to 17.0 (cm) 1 3(d)(ii) triangle method seen on graph 1 3(d)(iii) f within 10% of u0 1 Question Answer Marks 3(e) any difficulty in measuring hI e.g.: ruler in way of light / difficult to see top and bottom of image / edges of image blurred / difficult not to move screen when placing ruler to measure image 1 matching solution e.g.: use graph paper on screen / mark top and bottom of image and measure later/ use translucent screen and measure at back / use larger object / clamp screen (after obtaining focus) 1

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4 A student investigates the strength of an electromagnet. The electromagnet is made from a coil of insulated wire wrapped around an iron rod. When there is an electric current in the coil, the iron rod becomes magnetised. The electromagnet can then attract magnetic materials (e.g. iron and steel). Plan an experiment to investigate how one factor affects the number of steel paper clips the electromagnet can support. You are not required to carry out the experiment. The apparatus available includes: • an electromagnet, shown in Fig. 4.1 • a power supply • a selection of steel paper clips. In your plan, you should: • state a factor which can be measured and list any additional apparatus needed • state the key variables to be kept constant • explain briefly how to do the experiment, including any precautions to ensure reliable results (you may draw a diagram or add to Fig. 4.1 to help your explanation) • draw a table, or tables, 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. iron rod insulated wire Fig. 4.1 .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 4 MP1 apparatus: factor stated and apparatus appropriate to its measurement e.g. ammeter 1 MP2 control variable: any variable appropriate to independent variable (e.g. current if number of coils is the independent variable, number of coils if current is the independent variable. Same size / mass of paper clips) 1 MP3 method: measure independent variable check number of paper clips supported 1 MP4 repeat for new value of independent variable 1 MP5 table: columns, with units, for independent variable and number of paper clips 1 MP6 analysis: compare readings in the table to see if change in factor produces change in strength, 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 no of coils if current is factor) arrangement of paper clips 1

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