Cambridge IGCSE Physics 0625 — 2020 Oct/Nov Paper 5 · Variant 3

1 In this experiment, you will investigate the transfer of thermal energy from a beaker of hot water. Carry out the following instructions, referring to Fig. 1.1. Do not adjust the thermometer in the clamp. clamp thermometer lid beaker beaker clamp stand bench A B Fig. 1.1 (a) Pour 100 cm3 of hot water into beaker A. Place the thermometer in the water in beaker A by moving the clamp stand. In Table 1.1, record the temperature θ of the water at time t = 0 and immediately start the stopclock. Record, in Table 1.1, 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 beaker A by moving the clamp stand. [1] (b) (i) Repeat the procedure in (a) for beaker B. Remove the lid before pouring the hot water into the beaker. Replace the lid immediately after pouring. [2] (ii) Complete the headings and the values in the time t column in Table 1.1. [2] Table 1.1 beaker A beaker B without a lid with a lid t / θA / θB / 0 (c) Write a conclusion stating how using the lid affects the cooling of the water. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [1] (d) (i) Calculate the average rate of change of temperature xA of the water in beaker A. Use (θ0 − θ180) your values of θA from Table 1.1 and the equation xA = T where θ0 is the temperature of the water in beaker A at t = 0, θ180 is the temperature of the water at t = 180 s, and T = 180 s. Include a unit. xA = ......................................................... [1] (ii) Calculate the average rate of change of temperature xB of the water in beaker B. Use (θ0 − θ180) your values of θB from Table 1.1 and the equation xB = T where θ0 is the temperature of the water in beaker B at t = 0, θ180 is the temperature of the water at t = 180 s, and T = 180 s. Include a unit. xB = ......................................................... [1] (iii) Thermal energy is transferred from the surface of the water and from the sides of the beaker during this investigation. A student suggests that more thermal energy is transferred from the surface of the water than from the sides of the beaker. State whether your results support this suggestion. Justify your statement by reference to your values of xA, the average rate of change of temperature without a lid, and xB, the average rate of change of temperature with a lid. statement .......................................................................................................................... justification ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [2] (e) Suggest a change to the apparatus or the procedure to produce a greater difference between xA and xB. ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 11]

Mark scheme: 1(a) θ for beaker A decreasing 1 1(b)(i) θ for beaker B decreasing 1 more slowly than for A and all θ values to at least 1 °C 1 1(b)(ii) units all correct: s, °C, °C 1 t values all present (30, 60, 90, 120, 150 and 180) 1 1(c) conclusion matching results, e.g. beaker B cools more slowly / owtte 1 1(d)(i) °C / s 1 1(d)(ii) correct calculation of xA and xB and xA > xB 1 1(e)(iii) statement matching results 1 xB < half of xA / owtte 1 1(e) any suitable suggestion, e.g. • thicker / more insulated lid ; • higher initial temperature 1

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2 In this experiment, you will investigate circuits containing different combinations of resistors. Circuit A has been set up for you. Carry out the following instructions, referring to Fig. 2.1. power supply A X 2 Ω P Q V Circuit A Fig. 2.1 (a) Circuit A Switch on. Measure, and record in the first line of Table 2.1, the potential difference (p.d.) V across resistor X. Measure, and record in Table 2.1, the current I in the circuit. Switch off. Table 2.1 circuit V / I / R / Ω A B C [1] (b) Connect a second 2 Ω resistor between terminals P and Q so that it is in series with the first 2 Ω resistor, as shown in Fig. 2.2. The rest of the circuit must remain as in Fig. 2.1. This will form circuit B. 2 Ω 2 Ω P Q Fig. 2.2 Switch on. Measure, and record in Table 2.1, the potential difference (p.d.) V across resistor X. Measure, and record in Table 2.1, the current I in the circuit. Switch off. [2] (c) Connect a third 2 Ω resistor between terminals P and Q so that it is in series with the other 2 Ω resistors, as shown in Fig. 2.3. The rest of the circuit must remain as in Fig. 2.1. This forms circuit C. 2 Ω 2 Ω 2 Ω P Q Fig. 2.3 Switch on. Measure, and record in Table 2.1, the potential difference (p.d.) V across resistor X. Measure, and record in Table 2.1, the current I in the circuit. Switch off. Complete the headings in Table 2.1. [1] (d) (i) Calculate, and record in Table 2.1, a value for the resistance R of resistor X for each combination of resistors. V Use your readings from Table 2.1 and the equation R = . I [2] (ii) A student suggests that the values of R should be the same. State whether your results support this suggestion. Justify your statement by reference to values from your results. statement .......................................................................................................................... justification ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [2] (e) The results could be checked by using a different circuit. Draw, on Fig. 2.4, one other arrangement of three 2 Ω resistors between terminals P and Q. You are not required to connect this circuit. P Q Fig. 2.4 [1] (f) (i) A student wants to determine R by using a variable resistor to vary the current in the circuit. Draw the circuit symbol for a variable resistor. [1] (ii) Explain one advantage of using a variable resistor to vary the current compared to the procedure carried out in (a), (b) and (c). ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 11]

Mark scheme: 2(a) V all < 4.0 (V) 1 2(b) I all decreasing and < 1.00 (A) 1 V all to at least 1 dp and I all to at least 2 dp 1 2(c)(i) V, A 1 2(c)(ii) correct calculations of R 1 consistent 2 or consistent 3 sig figs 1 2(d) statement matching results 1 within limits of experimental accuracy / owtte with values or comparative values seen 1 2(e) any parallel or series and parallel arrangement of three resistors 1 2(f)(i) rectangle with strike-through arrow only 1 2(f)(ii) any suitable advantage, e.g. • can obtain continuous set of values • more straightforward to change current • can obtain more values easily 1

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3 In this experiment, you will investigate the magnification produced by a converging lens. Carry out the following instructions, referring to Fig. 3.1. illuminated object screen u lamp lens hO bench Fig. 3.1 (a) (i) Measure and record the height hO of the illuminated object. hO = ................................................... cm [1] (ii) Place the lens a distance u = 20.0 cm from the illuminated object. Place the screen near the lens and switch on the lamp. Move the screen until a clear focused image of the illuminated object is seen. Measure, and record in Table 3.1, the height hI of the image. Repeat the procedure for u = 25.0 cm, 30.0 cm, 35.0 cm and 40.0 cm. Switch off the lamp. Table 3.1 u / cm hI / cm W 20.0 25.0 30.0 35.0 40.0 [1] (b) For each distance u, calculate, and record in Table 3.1, a value W using your results from (a) hO and the equation W = . [1] hI (c) Plot a graph of u / cm (y-axis) against W (x-axis). [4] (d) The gradient of the line on the graph is numerically equal to the focal length f of the lens. Calculate a value of f for this experiment. Show clearly on the graph how you obtained the necessary information to determine the gradient. f = ........................................................ [2] (e) A student decides to extend the experiment using larger values of u. Use your results in Table 3.1 to explain why this could produce less reliable values for W. Suggest an improvement to overcome this difficulty. explanation ............................................................................................................................... ................................................................................................................................................... improvement ............................................................................................................................. ................................................................................................................................................... [2] [Total: 11]

Mark scheme: 3(a)(i) sensible value for hO (1.5 to 2.5 (cm)) 1 3(a)(ii) hI decreasing 1 3(b) W calculations correct 1 3(c) graph: axes labelled correct orientation, with quantity and unit 1 appropriate scales (plots occupying at least ½ grid) 1 plots all correct to less than ½ small square and precise plots 1 well-judged line and thin line 1 3(d) triangle method seen on graph 1 f in range 12 (cm) to 18 (cm) 1 3(e) any suitable explanation, e.g. • values of hI become very small / difficult to measure • greater % uncertainty 1 any suitable improvement, e.g. • use a larger object • use graph paper on screen • mark top and bottom of image and measure after 1

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4 A student investigates the factors that affect the average speed of a ball falling in water. Plan an experiment which will enable him to investigate the effect of one factor on the speed at which a ball of modelling clay falls in water. You are not required to carry out the experiment. The apparatus available includes: modelling clay that can be made into different sized balls metal ball bearings that can be embedded in the modelling clay a long transparent tube, closed at one end a supply of water In your plan, you should: • state clearly the factor to be investigated • list any additional apparatus needed • state any key variables to be kept the same • explain how to carry out the investigation, including the measurements to be made and any precautions that must be taken to ensure reliable results • explain how to use the readings to reach a conclusion. You may draw a diagram if it helps to explain your plan. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... .................................................................................................................................................. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [7]

Mark scheme: 4 MP1 Factor diameter / mass of ball 1 MP2 Apparatus stop-watch (or similar) 1 MP3 Control variable any suitable control variable, e.g. • mass of ball (if diameter is the factor) • diameter of ball (if mass is the factor) • distance (timed over) 1 MP4 Method any one from: • measure the chosen factor (i.e. mass / diameter) ; • apparatus used to measure mass / diameter ; • precaution: repeat (procedure) and average 1 MP5 Method drop ball in tube of water and time (over fixed distance) 1 MP6 Method repeat for different value of chosen factor (i.e. mass / diameter) 1 MP7 Analysis any one from: • comparison of time / speed with chosen factor • graph of time / speed vs chosen factor 1

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