Cambridge IGCSE Physics 0625 — 2021 Oct/Nov Paper 6 · Variant 3

1 A student investigates the effect of insulation on the cooling of water. She uses the apparatus shown in Fig. 1.1. The sides of beaker A are covered with material that is a thermal insulator. Beaker B has no covering on its sides. thermometer lid beaker A beaker B bench insulation Fig. 1.1 30 20 10 (a) Record room temperature θR shown on the thermometer in Fig. 1.1. θR = .......................................................... [1] (b) The student pours 150 cm3 of hot water into beaker A and records the temperature θ at time t = 0. She records, in Table 1.1, the temperature of the water in the beaker every 30 s. The student repeats the process for beaker B. 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 88.0 87.5 30 86.0 83.5 60 84.5 81.5 90 83.5 80.0 120 82.5 79.0 150 82.0 78.5 180 81.5 78.0 (c) Describe two precautions that can be taken to ensure that temperature readings in the experiment are as accurate as possible. 1. ............................................................................................................................................... ................................................................................................................................................... 2. ............................................................................................................................................... ................................................................................................................................................... [2] (d) Write a conclusion stating whether the insulation affects the rate of cooling of the water. Justify your answer by reference to values from the results. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (e) (i) Calculate the average cooling rate x1 during the first half of the experiment for the water in beaker B. Use the 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 the 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] (f) (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. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [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) for the comparison to be fair. State whether your results support this suggestion. Use your results from (e) to explain whether this precaution is necessary. statement .......................................................................................................................... explanation ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [2] [Total: 11]

Mark scheme: 1(a) θ R = 21 (°C) 1 1(b) s, °C both correct 1 1(c) 2 suitable precautions e.g.: view scale reading perpendicularly, wait until readings stops rising (at start), avoid thermometer touching beaker 2 1(d) statement matching readings in table 1 comparison of temperature changes over 180 s, matching statement (need to see values used in justification) 1 1(e)(i) correct calculation of x1 1 1(e)(ii) Correct unit °C / s 1 1(f)(i) beaker B without lid 1 1(f)(ii) statement matching data for beaker B with values quoted 1 statement with comparison of data or cooling rates 1

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2 A student compares the resistances of two wires. She uses the circuit, part of which is shown in Fig. 2.1. X Y crocodile clip resistance wire A l resistance wire B Fig. 2.1 (a) On Fig. 2.1, complete the circuit diagram to show a voltmeter connected to measure the potential difference (p.d.) across terminals X and Y, and an ammeter connected to measure the current in the circuit. [2] (b) The student connects the crocodile clip to a length l = 90.0 cm of resistance wire A and measures the potential difference V and the current I for the length l of the wire. 2 3 0.4 0.6 1 4 0.2 0.8 0 5 0 1.0 V A Fig. 2.2 Fig. 2.3 (i) Read, and record in Table 2.1, the values of V and I shown on the meters in Fig. 2.2 and Fig. 2.3. [2] Table 2.1 wire l / cm V / I / R / A 90.0 B 90.0 2.6 0.45 A 50.0 2.7 0.54 B 50.0 2.3 0.72 (ii) The student then connects the crocodile clip to lengths l = 90.0 cm of wire B, l = 50.0 cm of wire A and l = 50.0 cm of wire B. Her readings are shown in Table 2.1. Calculate, and record in Table 2.1, the resistance R of each length of wire A and wire B. Use the values of V and I and the equation V R = . I [2] (iii) 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 = ................................................................ 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] (ii) 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) ammeter in series connection or voltmeter in parallel connection 1 second meter shown connected correctly and circuit complete 1 2(b)(i) V = 2.8 1 I = 0.32 1 2(b)(ii) R = 8.75 / ecf, 5.78, 5.00, 3.19 1 R consistent to 2 or 3 significant figures 1 2(b)(iii) V, A, Ω all correct 1 2(c)(i) P = 1.51 / ecf and Q = 1.57 / ecf 1 2(c)(ii) 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 A student investigates the image produced by a converging lens. He uses the apparatus shown in Fig. 3.1. triangular screenobject u lens hO bench Fig. 3.1 (a) The triangular object is shown full size in Fig. 3.2. Measure and record the height hO of the triangular object in Fig. 3.2. hO = ..................................................... cm [1] hO Fig. 3.2 (b) The student sets the distance u between the triangular object and the lens to 20.0 cm. He moves the screen until a sharp image of the triangular object is seen on the screen. The student measures, and records in Table 3.1, the height hI of the image on the screen. Briefly describe a technique to obtain an image on the screen that is as sharp as possible in this experiment. ................................................................................................................................................... ............................................................................................................................................. [1] (c) The student repeats the process for u = 25.0 cm, u = 30.0 cm, u = 35.0 cm and u = 40.0 cm. His readings are shown in Table 3.1. 1 For distance u = 20.0 cm, calculate, and record in Table 3.1, the value of . [1] hI Table 3.1 1 1 u / cm hI / cm  cm hI 20.0 5.6 25.0 3.2 0.31 30.0 1.9 0.53 35.0 1.5 0.67 40.0 1.2 0.83 1 1(d) Plot a graph of u / cm (y-axis) against (x-axis).  cm hI [4] (e) (i) Determine the gradient of the graph. Show clearly on the graph how you obtained the necessary information. gradient = .......................................................... [1] (ii) 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 (e)(i). f = .......................................................... [1] (f) 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) hO = 2.0 (cm) 1 3(b) move screen backwards and forwards / move screen slowly 1 3(c) 1 / hI = 0.18 1 3(d) 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 line and thin line 1 3(e)(i) triangle method seen on graph 1 3(e)(ii) f in range 14.0cm to 16.0cm 1 3(f) 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. 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, voltmeter, coils ( no apparatus for measuring required ) 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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