Cambridge IGCSE Physics 0625 — 2018 Oct/Nov Paper 5 · Variant 3

1 In this experiment, you will determine the density of modelling clay. Carry out the following instructions, referring to Fig. 1.1. w modelling clay h l Fig. 1.1 (a) (i) Measure the length l, width w and height h of the block of modelling clay. l = ........................................................ cm w = ........................................................ cm h = ........................................................ cm [1] (ii) Calculate the volume V1 of the block, using your measurements from (a)(i) and the equation V1 = l × w × h. V1 = .................................................. cm3 [1] (b) Suggest a possible source of inaccuracy in measuring the block and describe an improvement to the procedure that will produce more reliable measurements of the block. suggestion ................................................................................................................................ ................................................................................................................................................... improvement ............................................................................................................................. ................................................................................................................................................... ................................................................................................................................................... [2] forcemeter loop of string modelling clay Fig. 1.2 (c) Measure the weight W of the block of modelling clay, as shown in Fig. 1.2. W = ..................................................... N [1] (d) Calculate a value ρ1 for the density of the modelling clay, using your results from (a)(ii) and W × k (c) and the equation ρ1 = , where k = 100 g / N. V1 ρ1 = ......................................................... [2] measuring cylinder modelling clay Fig. 1.3 (e) • Pour approximately 150 cm3 of water into the measuring cylinder. • Record the volume V2 of the water in the measuring cylinder. V2 = ....................................................... cm3 • Remove the loop of string from the forcemeter and lower the block of modelling clay carefully into the water in the measuring cylinder as shown in Fig. 1.3. • Record the new reading V3 of the measuring cylinder, with the piece of modelling clay in the water. V3 = ....................................................... cm3 [1] (f) Describe how a measuring cylinder is read to obtain a value for the volume of water. You may draw a diagram to help you. ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [1] (g) (i) Calculate another value ρ2 for the density of modelling clay, using your readings from (c) W × k and (e) and the equation ρ2 = , where k = 100 g / N. (V3 – V2) ρ2 = ......................................................... [1] (ii) Suggest which of ρ1 or ρ2 is likely to be the more accurate value for the density of the modelling clay. Justify your answer by referring to the procedure. ........................................................................................................................................... ........................................................................................................................................... ...................................................................................................................................... [1] [Total: 11]

Mark scheme: 1(a)(i) 1 1(a)(ii) correct calculation of V1 from candidate’s values 1 1(b) difficult to measure irregular dimensions / owtte 1 repeat (in several places for each dimension and take averages) 1 1(c) sensible value for W 1 1(d) ρ1 in range 1.3 to 2.3 1 unit g / cm3 1 1(e) V3 > V2 1 1(f) line of sight perpendicular; read to bottom of meniscus. 1 1(g)(i) ρ2 within 10% of ρ1 1 1(f)(ii) suggestion supported by valid reason e.g. ρ2 as volume is measured directly; ρ1 as measuring cylinder is less precise; string adds to volume displaced. 1

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2 In this experiment, you will determine the resistance per unit length of wire X. The circuit has been set up for you. power supply wire X V A crocodile clip C resistance wire Fig. 2.1 (a) Carry out the following instructions, referring to Fig. 2.1. • Connect the crocodile clip C to the free end of the resistance wire. • Switch on. Adjust the position of the crocodile clip C until the current shown on the ammeter is as near to 0.40 A as possible. • Measure, and record in Table 2.1, the potential difference (p.d.) V across wire X. Switch off. • Repeat the procedure for I = 0.50 A, 0.60 A, 0.70 A and 0.80 A. Table 2.1 I / A V / V 0.40 0.50 0.60 0.70 0.80 [2] (b) Plot a graph of V / V (y-axis) against I / A (x-axis). [4] (c) (i) Determine the gradient G of the graph. Show clearly on the graph how you obtained the necessary information. G = ......................................................... [1] (ii) Measure the length l of wire X. l = ................................................... cm [1] G × k (iii) Calculate the resistance R of each centimetre of wire X, using the equation R = , l where k = 1.0 Ω cm. Give the value for R, to a suitable number of significant figures for this experiment. R = ......................................................... [2] (d) A student discovers that the resistance wire becomes very hot when the crocodile clip is connected to short lengths of the wire. Suggest an improvement that would help to reduce this effect. ................................................................................................................................................... ................................................................................................................................................... .............................................................................................................................................. [1] [Total: 11]

Mark scheme: 2(a) V values all increasing 1 V all < 3.00 V and to at least 1 dp 1 2(b) 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 2(c)(i) G present and triangle method seen on graph 1 2(c)(ii) l in range 10 to 20 (cm) 1 2(c)(iv) R in range 0.05 to 0.11 1 2 / 3 sig figs and unit = Ω or Ω / cm 1 2(d) Any one from: use smaller current / potential difference; use wire with greater resistance; open switch / switch off circuit in between readings. 1

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3 In this experiment, you will investigate the reflection of light by a plane mirror. ray-trace sheet eye hole C α A N B D Fig. 3.1 (a) Carry out the following instructions, using the separate ray-trace sheet provided. Refer to Fig. 3.1 for guidance. • Draw a line about 10 cm from the bottom of your ray-trace sheet. Label this line AB. • Mark a point N, near the centre of AB. • Draw a normal to AB at point N, towards the top of the page. Label the other end of this normal line L. [1] (b) Draw a line CD passing through N and at an angle α to AB where α = 20°. [1] (c) • Place two pins P1 and P2 on line LN, a suitable distance apart for ray tracing. Label the positions of P1 and P2. • Place the reflecting surface of the mirror on line CD and view the images of P1 and P2 from the direction indicated by the eye in Fig. 3.1. • Place two pins P3 and P4 some distance apart so that the images of P1 and P2, and the pins P3 and P4, all appear exactly one behind the other. Label the positions of P3 and P4. • Remove the mirror and the pins. • Draw a line passing through the P3 and P4 positions and reaching LN. • Measure and record in Table 3.1, the angle θ between this line and the normal LN. Table 3.1 α/ ° θ/ ° 20 35 [3] (d) Repeat steps (b) and (c) for an angle α = 35°, replacing pins P1 and P2 in their original positions in step (c). [2] (e) A student suggests that when the mirror is moved, the change in θ should be equal to twice the change in α. State whether your readings support this idea. Justify your answer with reference to the readings. statement .................................................................................................................................. justification ................................................................................................................................ ................................................................................................................................................... ................................................................................................................................................... [2] (f) Suggest two precautions that you took to ensure accurate results from this type of experiment. 1 ................................................................................................................................................ ................................................................................................................................................... 2 ................................................................................................................................................. ................................................................................................................................................... [2] [Total: 11] Tie your ray trace sheet between pages 10 and 11.

Mark scheme: 3(a) 1 3(b) α = 20° ± 1° 1 3(c) P1 P2 pin separations ⩾ 5.0 cm 1 line in correct place and neat 1 θ = 40° ± 2° 1 3(d) line in correct place and neat 1 θ = 70° ± 2° 1 3(d) statement matching results including qualitative justification (e.g. ‘within limits of experimental accuracy’ / owtte) 1 justification that makes use of the data to support statement 1 3(e) Any two suitable precautions: pins upright / view pins at base; thin pins; thin lines / sharp pencil; large pin separations; ensure mirrored surface lies along drawn line. 2

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4 A student is investigating the conduction of thermal energy by metals. Plan an experiment to compare the rates at which different metals conduct thermal energy. You are not required to carry out the experiment. The apparatus available includes: strips of different metals, shaped as shown in Fig. 4.1 a test-tube in a clamp stand a beaker a supply of cold water a supply of hot water. Fig. 4.1 The shorter section of each strip of metal can fit inside a test-tube. Write a plan for the experiment. You should: • list any additional apparatus needed • draw a labelled diagram of how the apparatus will be arranged • explain briefly how you will carry out the experiment • explain how the metals will be compared • state the precautions which should be taken to obtain reliable results. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [7] [Total: 7]

Mark scheme: 4 MP1 Apparatus thermometer AND stopwatch / (stop)clock / timer 1 MP2 Diagram workable arrangement 1 MP3 Method hot water in beaker and cold water in test-tube AND measure (start and) end temperatures in test-tube AND over measured time 1 MP4 Method repeat for different metals 1 MP5 Comparison calculation of (rate of) temperature rise / heating curves for different metals 1 MP6 and MP7 Precautions Any two from: same start temperatures (of hot / cold water); same duration of experiment; same volume of cold water (being heated); repeat experiment and take average (of calculated values); use of insulation; stir (cold) water; heat to keep water in beaker at constant temperature. 2

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