Cambridge IGCSE Physics 0625 — 2014 May/June Paper 5 · Variant 3

1 In this experiment, you will determine the density of water using two methods. (a) Method 1 Carry out the following instructions, referring to Figs. 1.1 and 1.2. measuring cylinder water balance Fig. 1.1 Fig. 1.2 (i) Place the empty measuring cylinder on the balance as shown in Fig. 1.1. Measure and record the mass m1 of the empty measuring cylinder. Remove the measuring cylinder from the balance. m1 = ..................................................g (ii) Pour approximately 70 cm3 of water into the measuring cylinder. Measure and record the volume V1 of the water. V1 = ............................................. cm3 (iii) Place the measuring cylinder containing the water on the balance as shown in Fig. 1.2. Measure and record the mass m2 of the measuring cylinder and water. m2 = ..................................................g [2] Leave the water in the measuring cylinder for use in Method 2. Remove the measuring cylinder from the balance. (iv) Calculate a value ρ1 for the density of water using the equation ρ1 = m2 – m1. Give an V1 appropriate unit. ρ1 = ................................................[1] (b) Method 2 Carry out the following instructions, referring to Figs. 1.3 and 1.4. test-tube air cotton Fig. 1.3 Fig. 1.4 (i) Place the empty test-tube on the balance as shown in Fig. 1.3. Measure and record the mass m3 of the test-tube. m3 = ..................................................g (ii) Carefully lower the test-tube, by means of the cotton, into the measuring cylinder until it floats as shown in Fig. 1.4. Measure and record the new water level V2 in the measuring cylinder. V2 = ............................................. cm3 (iii) Using your results from (a)(ii) and (b)(ii), calculate V3, the change in the water level, where V3 = (V2 – V1). V3 = ............................................. cm3 [2] (iv) Calculate and record a value ρ2 for the density of water using the equation ρ2 = m3 . V3 ρ2 = ................................................[1] (c) Calculate an average value ρAV for the density of water using your results from (a)(iv) and (b)(iv). ρAV = ................................................[1] (d) Suggest a precaution that should be taken in Method 1 to ensure that the volume reading is as accurate as possible. You may draw a diagram. ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[1] (e) Suggest a possible source of experimental inaccuracy in Method 2, other than with the volume reading. State and explain the effect that this would have on your value for ρ2. suggestion ................................................................................................................................ ................................................................................................................................................... effect and explanation ................................................................................................................ ................................................................................................................................................... [2] [Total: 10] Turn over for Question 2

Mark scheme: 1 (a)(i)(ii) m1 and m2 present and in g and V1 in cm3 [1] (iii) m2 > m1 [1] (iv) unit of g / cm3 or kg / m3 seen in (a), (b) or (c) and not contradicted (unit must match value) [1] (b)(i)(ii) m3 present and V2 present with V2 > V1 [1] (iii) correct calculation of V3 [1] (iv) ρ2 to 2 / 3 sig. figs. [1] (c) ρAV in range 0.9 to 1.1 (or 900 to 1100) [1] (d) any one from: • take reading perpendicularly / at right angles to scale • read bottom of meniscus • other suitable precaution [1] (e) appropriate source of inaccuracy, other than in (d) e.g. balance not at zero / test-tube catches on side of measuring cylinder [1] matching effect on ρ with explanation e.g. ρ greater as mass reading larger / ρ greater as volume smaller [1] [Total: 10]

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2 In this experiment, you will investigate the cooling of water. Carry out the following instructions, referring to Fig. 2.1. The thermometer must remain in the clamp throughout the experiment, at the same height. thermometer beaker A B Fig. 2.1 (a) (i) Pour approximately 200 cm3 of hot water into beaker A. (ii) Wait for about 30 seconds before taking any measurements. (iii) Start the stopclock and read the thermometer. In the top row of Table 2.1, record this temperature θ at time t = 0. (iv) In the table, record the temperature θ of the water at times t = 30 s, 60 s, 90 s, 120 s,150 s and 180 s. (v) Complete the column headings in the table. (vi) Carefully remove the thermometer from beaker A. Place the thermometer in beaker B. Table 2.1 beaker A beaker B with approximately with approximately 200 cm3 of water 100 cm3 of water t / θ/ θ/ [5] (b) (i) Pour approximately 100 cm3 of hot water into beaker B. (ii) Repeat (a)(ii) to (iv) for beaker B. (c) Describe a similarity in the patterns of temperature change of the two volumes of water, apart from the fact that the temperature of each decreases. ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[1] (d) A student suggests that the rate of cooling is smaller for a larger volume of water than for a smaller volume of water. State whether your readings support this suggestion. Justify your answer by referring to your readings. statement ................................................................................................................................... justification ................................................................................................................................. ................................................................................................................................................... ................................................................................................................................................... [2] (e) Another IGCSE student wants to repeat your experiment in order to check the results. Suggest two factors that should be kept the same in order for the comparison to be fair. 1. ............................................................................................................................................... ................................................................................................................................................... 2. ............................................................................................................................................... ................................................................................................................................................... [2] [Total: 10]

Mark scheme: 2 (a)(b) units correct in symbols or words, s, °C, °C [1] t values correct 0, 30, 60, 90, 120, 150, 180 [1] θ for 200 cm3 decreasing [1] θ for 100 cm3 decreasing and evidence of θ to at least 1 °C [1] larger / same change over 180 s for 100 cm3 [1] (c) appropriate definite pattern which fully matches candidate’s results e.g. rate of temperature drop greater at start than at end NOT stated pattern which partly matches results [1] (d) statement matching temperature changes (accept ‘no significant difference’ if appropriate) [1] justification referring to results and involving comparative change in temperature with specific mention of in the same time [1] IGCSE – May/June 2014 0625 53 (e) any two from: • room temperature / external temperature (but not outside temperature / environmental factor such as draughts / sunshine • initial water temperature / start temperature • same amount of stirring / wait same time before reading • keep thermometer at same depth • same size / thickness / material / surface area of beaker • same volumes of water [2] [Total: 10]

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3 In this experiment, you will investigate resistance using a set of wires. The circuit in Fig. 3.1 has been set up for you. Carry out the following instructions, referring to Fig. 3.1. power supply A V crocodile clips Fig. 3.1 (a) (i) Connect the crocodile clips to the ends of wire A. (ii) Switch on. Measure, and record in Table 3.1, the potential difference V and the current I. Switch off. Table 3.1 wire V / I / A B C [3] (b) (i) Disconnect wire A and connect the crocodile clips to the ends of wire B. (ii) Repeat step (a)(ii). (c) (i) Disconnect wire B and connect the crocodile clips to the ends of wire C. (ii) Repeat step (a)(ii). (d) Complete the column headings in the table. (e) (i) Calculate and record the resistance R of each wire, using your readings from the table and the equation R = . V–I resistance of wire A, RA = .................................................... resistance of wire B, RB = .................................................... resistance of wire C, RC = .................................................... [3] (ii) A student suggests that RA should be equal to RB + RC. State whether your findings support this suggestion. Justify your answer by reference to your results. statement ........................................................................................................................... ........................................................................................................................................... justification ......................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... [1] (f) One problem encountered in this type of investigation is that resistance can be affected by a rise in temperature of the wire. Suggest one way in which this effect could be kept to a minimum. ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[1] (g) In a variation of this experiment, an IGCSE student wants to change the current in wire A using a variable resistor (rheostat). (i) In the space below, draw the standard circuit symbol for a variable resistor. (ii) On Fig. 3.1, mark with an X where the variable resistor could be connected so that it may be used in this way. [2] [Total: 10]

Mark scheme: 3 (a)(b)(c) p.d.s all < 3.0 V and to at least 1d.p. [1] currents all < 1.50 A and to at least 2 d.p. [1] (d) units both correct, symbols or words, V, A [1] (e) (i) R calculations correct [1] correct unit seen at least once and not contradicted [1] consistent 2 or consistent 3 sig. figs. for R [1] (ii) statement matches results (expect ‘Yes’ but allow ‘No’ if difference >10%) with matching and correct justification (which refers to figures) e.g. ‘within limits of expt accuracy’ owtte if ‘Yes’ or ‘too different’ owtte if ‘No’ [1] (f) any one from: • switch off between readings • only switch on for short time • use smaller currents / p.d.s • suitable means of dissipating thermal energy [1] (g) (i) correct circuit symbol (rectangle with strike-through arrow only) [1] (ii) X shown in series circuit (not between crocodile clips) [1] [Total: 10]

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4 In this experiment, you will investigate shadows. Carry out the following instructions, referring to Fig. 4.1. lamp object screen card d D Fig. 4.1 The lamp, card and screen have been set up for you. The card is to protect your eyes from the glare of the lamp and should remain at the side of the lamp. (a) (i) Set the distance D between the centre of the lamp and the screen to 60 cm. Do not change this distance during the experiment. (ii) Place the object at a distance d = 55 cm from the centre of the lamp so that it produces a shadow on the screen. (iii) Measure, and record in Table 4.1, the width w and the height h of the shadow of the square object. Table 4.1 d / cm w / cm h / cm s / cm 55 45 35 25 20 15 [2] (iv) Repeat (a)(iii) for d values of 45 cm, 35 cm, 25 cm, 20 cm and 15 cm. (b) (i) For each distance d, calculate, and record in the table, a value for the average side length w + h s, using your readings for w and h and the equation s = . 2 (ii) The object you are using is square in shape. State a practical reason why it is useful to calculate s rather than just rely on w or h to show the size of the shadow. ........................................................................................................................................... .......................................................................................................................................[1] (c) Plot a graph of s / cm (y-axis) against d /cm (x-axis). [5] (d) A value of d = 20 cm has been inserted between d = 25 cm and d = 15 cm. This does not follow the pattern of the gaps of 10 cm between the other distances. Explain why it is useful to have this value when drawing the line on the graph. ................................................................................................................................................... ...............................................................................................................................................[1] (e) A student suggests that the distance between the lamp and the object in this experiment should be no less than 15 cm. From your observations, give a reason why this is a sensible suggestion. ................................................................................................................................................... ...............................................................................................................................................[1] [Total: 10]

Mark scheme: 4 (a) all w and h present and both increasing [1] (b) (i) correct s calculations [1] IGCSE – May/June 2014 0625 53 (ii) appropriate reason e.g. • w and h not the same (need reference to square shape) • difficult to measure shadows / edges not distinct • card might not be perpendicular / card might be tilted • lamp is not a point source • improve reliability [1] (c) axes labelled with quantity and unit [1] scales appropriate, plots covering at least ½ grid [1] plots correct to ½ small square [1] well judged curve [1] thin, continuous line, precise plots [1] (d) large gap between plots for 25 and 15 cm [1] allow ‘ensure curve is consistent’, ‘gaps becoming larger’ but NOT ‘more plots, more accurate’, ‘make line more accurate’ (e) any suitable reason e.g. • shadow would be too big (for screen) • difference between w and h becomes larger • shadows become less distinct / more blurred / too distorted [1] [Total: 10]

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