Cambridge IGCSE Physics 0625 — 2019 Feb/March Paper 5 · Variant 2

1 In this experiment, you will investigate the reflection of light by a plane mirror. Carry out the following instructions, using the separate ray-trace sheet provided. You may refer to Fig. 1.1 for guidance. hole C E A 10 cm ray-trace sheet θ lamp N L screen with slit 4 cm B F D Fig. 1.1 (a) • Draw a line AB 4 cm from the edge of the ray-trace sheet and in the middle of the paper, as shown in Fig. 1.1. • Draw a line CD parallel to line AB and 10 cm from it. • Draw a normal to line AB at a point N in the centre of line AB. Point N must be an equal distance from the top and bottom of the sheet. • Extend the normal to line CD and label the point at which it crosses line CD with the letter L. [1] (b) Draw a line EF, through point N, as shown in Fig. 1.1 and at an angle θ = 5°. [1] (c) • Place the plane mirror on line EF with the reflecting surface facing to the right. • Place the screen with a slit on line CD and arrange the lamp so a ray of light shines along line LN. • Mark the ray that is reflected from the mirror, using a small cross at a suitable distance from point N. Label this cross G. • Remove the mirror, screen and lamp from the ray-trace sheet. [1] (d) • Draw a line joining point N and point G. Extend this line until it meets line CD. • Label the point at which line NG meets line CD with the letter H. • Measure, and record in Table 1.1, the length a of line LH. [1] (e) Repeat (b), (c) and (d) for values of θ = 10°, 15°, 20° and 25°. Table 1.1 θ / ° a / cm 5 10 15 20 25 [1] (f) Plot a graph of a / cm (y-axis) against θ / ° (x-axis). [4] (g) Suggest a possible source of inaccuracy in this experiment, even if it is carried out carefully. ................................................................................................................................................... ............................................................................................................................................. [1] (h) A student wishes to check if his values for a are reliable. Suggest how he could extend the experiment, using the same apparatus, to check the reliability of his results. You are not required to carry out this extended experiment. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 11] Tie your ray-trace sheet into this question paper between pages 2 and 3.

Mark scheme: 1(a) AB, CD and normal correct 1 1(b) θ = 5° ± 1° 1 1(c) GN ⩾ 5.0 cm 1 1(d) all lines present, correct and neat 1 1(e) 5 correct values of a, increasing 1 1(f) graph: • axes labelled 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 continuous line 1 1(g) any suitable reason e.g.: ray has finite thickness – (difficult to mark position of ray precisely), reflecting surface of mirror at rear, inaccuracies have more effect for smaller angles, small variations in mirror angle have significant effect on ‘a’ 1 1(h) reflect ray below NL at same angles and take averages 1

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2 In this experiment, you will investigate how the use of a lid or insulation affects the rate of cooling of hot water in a beaker. Carry out the following instructions, referring to Fig. 2.1. thermometer insulation lid beaker A beaker B bench Fig. 2.1 (a) The thermometer must remain in the clamp throughout the experiment. • Use the measuring cylinder to pour 100 cm3 of hot water into beaker A. • Place the thermometer in the water in beaker A. • In the first row of Table 2.1, record the temperature θ of the water at time t = 0 and immediately start the stopclock. • Record, in Table 2.1, the temperature θ of the water at times t = 30 s, 60 s, 90 s, 120 s, 150 s and 180 s. • Remove the thermometer from the beaker. [1] (b) (i) Repeat (a) for beaker B. Ensure that the lid is removed before pouring the hot water into the beaker. Replace the lid immediately after pouring. [2] (ii) Complete the headings and the time column in the table. [2] Table 2.1 beaker A beaker B with insulation with a lid only only t / θ/ θ/ 0 (c) Write a conclusion stating whether the insulation or the lid is more effective in reducing the cooling rate of the water in the beakers in this experiment. Justify your answer by reference to your results. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (d) A student thinks that the experiment does not show how effective insulation is on its own or how effective a lid is on its own. Suggest an additional experiment which could be used to show how effective a lid or insulation is on its own. Explain how the additional results could be used. You are not required to carry out this experiment. additional experiment ............................................................................................................... ................................................................................................................................................... ................................................................................................................................................... explanation ............................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... [2] (e) Students in another school are carrying out this experiment using equipment which is identical to yours. State whether it is important for the students to make the initial temperature of the water the same as yours if they are to obtain average cooling rates that are the same as yours. Assume that the room temperature is the same in each case. Use values from your results for beaker A in Table 2.1 to justify if this factor should be controlled. statement .................................................................................................................................. ................................................................................................................................................... explanation ............................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... [2] [Total: 11]

Mark scheme: 2(a) 1 2(b)(i) θ for B decreasing and recorded to at least 1 °C 1 decreasing more slowly 1 2(b)(ii) s, °C, °C all correct 1 30, 60, 90, 120, 150, 180 1 2(c) conclusion matching results 1 correct mention of comparative temperature change over 180 s, supporting conclusion 1 2(d) additional experiment with both insulation and lid / neither insulation nor lid 1 compare result of (previous) experiment with additional / only one factor changed in (each) comparison 1 2(e) statement matching results 1 comparison of temperature difference over first 30 s and last 30 s 1

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3 In this experiment, you will investigate a resistance wire. The circuit has been set up for you. Carry out the following instructions, referring to Fig. 3.1. power supply A V crocodile clip metre rule 0.0 cm mark l resistance wire Fig. 3.1 (a) • Connect the crocodile clip to a length l = 90.0 cm of the resistance wire. • Switch on. • Record, in Table 3.1, the value of potential difference (p.d.) V and current I for the wire. • Switch off. • Move the crocodile clip and repeat the procedure for lengths of resistance wire l = 60.0 cm and l = 40.0 cm. [3] (b) Complete the column headings in Table 3.1. [1] Table 3.1 R Ω l / cm V / I / R / Ω l cm / (c) (i) Calculate, and record in Table 3.1, the resistance R of each length l of the wire. V Use your readings from the table and the equation R = . I [2] R (ii) Calculate, and record in Table 3.1, the value of for each wire. l [1] (d) Use your results in Table 3.1 to calculate the resistance R25 of a 25.0 cm length of the resistance wire. Show your working. You must not carry out an experiment to measure this value. Ω [1] R25 = ...................................................... (e) Suggest one reason why different students, carrying out the experiment carefully with the same equipment, may not obtain identical results. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [1] (f) A student finds that, during the experiment, the wire becomes hot because of a high current. He decides to use a variable resistor to prevent this. Complete the circuit in Fig. 3.2 to show a variable resistor used for this purpose in the experiment. You are not required to carry out this experiment. power supply resistance wire Fig. 3.2 [2] [Total: 11]

Mark scheme: 3(a) V <3.00 (V) 1 I <1.50 (A) and increasing 1 V all to 1dp at least and I all to 2dp at least 1 3(b) correct units: V, A 1 3(c)(i) correct calculations of R 1 consistent 2 or consistent 3 sig. figs. 1 3(c)(ii) correct calculations or R / l 1 3(d) R25 in range 1 Ω to 3 Ω and clear method seen e.g. proportion from other value(s) of R or use of R / l value(s) 1 3(e) any one from: difficult to judge position of crocodile clip, difficult to measure wire to nearest mm, contact between wire and crocodile clip not precise, difficult to interpolate readings on meters between marks 1 3(f) correct symbol for variable resistor 1 in series and with all circuit elements in correct arrangement 1

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4 A student wants to investigate the effect of air resistance on the swing of a pendulum. Plan an experiment which will enable him to investigate how air resistance changes the way in which a pendulum swings. You are not required to carry out the experiment. The apparatus available includes: a light wooden rod, approximately 80 cm long with a hole at one end, through which a nail will fit a piece of modelling clay to act as a pendulum bob, as shown in Fig. 4.1 a sheet of thick card which will provide the air resistance when the pendulum swings. In your plan, you should: • list any additional apparatus needed • explain briefly how you would carry out the experiment including exactly which measurements should be taken • state the key variables that you would control • draw a table, or tables, with column headings, to show how you would display your readings (you are not required to enter any readings in the table) • explain how you would use your readings to reach a conclusion. You may add to Fig. 4.1 or draw an additional diagram if it helps to explain your plan. nail wooden rod bob Fig. 4.1 .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7] [Total: 7]

Mark scheme: 4 MP1 apparatus: means of measuring dependent variable (e.g. stop watch / rule / protractor) 1 MP2 method (one from): workable means of providing air resistance (e.g. fix card to rod / bob), allow pendulum to swing, suitable measurement (e.g. period, amplitude) 1 MP3 repeat for different value of independent variable (e.g. area of card) 1 MP4 control variable (one from): length of pendulum, angle of release, mass of bob 1 MP5 table: suitable clear format with column headings and units 1 MP6 analysis: compare readings to see if change in air resistance produces change in dependent variable (e.g. change in area of card changes period) / plot graph 1 Question Answer Marks 4 MP7 additional point (one from): time 10 oscillations / swings (and calculate period), small angle of swing, at least 5 sets of data taken, repeat each measurement and take average, adjust mass of pendulum to compensate for changing mass of card, repeat with different length of pendulum / mass of bob, length measured to centre of bob / centre of gravity of pendulum, use of fiducial aid 1

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