Cambridge IGCSE Physics 0625 — 2020 Feb/March Paper 5 · Variant 2

1 In this experiment, you will determine the density of wood by two methods. Carry out the following instructions, referring to Fig. 1.1. l wooden rod d loop of thread Fig. 1.1 Method 1 (a) (i) Use a ruler to measure the length l and the diameter d of the wooden rod you are using. l = ........................................................ cm d = ........................................................ cm [2] (ii) Suggest a more accurate method for measuring the diameter of the rod. List any additional apparatus you would require and briefly describe how you would determine the diameter. You may draw a diagram if it helps to explain your answer. You are not asked to carry out this method. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [2] (b) Measure the mass m of the wooden rod using the balance provided. m = ........................................................... g [1] (c) Calculate a value ρ1 for the density of the wooden rod. Use your values from (a)(i) and (b) 4 m and the equation ρ1 = . Include a suitable unit. π d 2 l ρ1 = .............................................................. [2] Method 2 (d) (i) Pour approximately 150 cm3 of water into the measuring cylinder. Record the reading V1 of the water level in the measuring cylinder. V1 = ...................................................... cm3 Gently lower the wooden rod into the water so that it floats freely as shown in Fig. 1.2. measuring cylinder water Fig. 1.2 Record the new reading V2 of the water level in the measuring cylinder. V2 = ...................................................... cm3 [1] (ii) On Fig. 1.2, draw an arrow on the left‑hand side showing the correct line of sight for reading the volume of water in the measuring cylinder. [1] (e) Fig. 1.3 Fig. 1.4 Remove the rod from the measuring cylinder and lower the modelling clay into the water until it is completely submerged as shown in Fig. 1.3. Record the new reading V3 of the water level in the measuring cylinder. V3 = ...................................................... cm3 Remove the modelling clay from the measuring cylinder. Attach the rod to the modelling clay using the hook on the modelling clay and the loop of thread on the rod as shown in Fig. 1.4. Lower the modelling clay and rod into the water until the rod is completely submerged. Record the new reading V4 of the water level in the measuring cylinder. V4 = ...................................................... cm3 Calculate another value ρ2 for the density of the wooden rod. (V2 – V1) × k where k = 1.0 g / cm3. Use your values from (d) and (e) and the equation ρ2 = (V4 – V3) ρ2 = .............................................................. [2] [Total: 11]

Mark scheme: 1(a)(i) 1 both to 1 decimal place 1 1(a)(ii) method outlined / how diameter determined accurately e.g. use of string wrapped round rod and measured / several turns and calculate diameter from circumference, OR use of rod between two blocks and measure gap / in at least 2 places and take average, OR means of measuring diameter across ends / at several places and take average, OR use of micrometer, (vernier) callipers / at various points (along length or across ends) and take average 2 1(b) m in suitable range (5–15 g) 1 1(c) ρ1 in suitable range >0.5, <1.0 1 correct unit (g / cm3) 1 1(d)(i) V2 > V1 1 1(d)(ii) arrow perpendicular to measuring cylinder and in line with bottom of meniscus 1 Question Answer Marks 1(e) ρ2 correctly calculated 1 within 10% of ρ1 1

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2 In this experiment, you will investigate the cooling of hot water in a beaker. Carry out the following instructions, referring to Fig. 2.1. thermometer beaker bench Fig. 2.1 (a) (i) Measure the room temperature θ R shown on the thermometer. θ R = .............................................................. [1] (ii) Pour 150 cm3 of hot water into the beaker. Place the thermometer in the water in the beaker. In the first row of Table 2.1, record the temperature θ of the water at time t = 0 and immediately start the stop‑clock. In Table 2.1, record the temperature θ of the water at times t = 30 s, 60 s, 90 s, 120 s, 150 s, 180 s, 210 s, 240 s and 270 s. [1] (b) Complete the headings in Table 2.1. [1] Table 2.1 t / θ/ 0 30 60 90 120 150 180 210 240 270 (c) (i) Calculate the average cooling rate x1 during the first 90 s of the experiment. Use your readings from Table 2.1 and the equation θ0 – θ90 x1 = T where T = 90 s and θ0 and θ90 are the temperatures at t = 0 and t = 90 s. Include the unit for the cooling rate. x1 = .............................................................. [1] (ii) Calculate the average cooling rate x2 during the middle 90 s of the experiment. Use your readings from Table 2.1 and the equation θ90 – θ180 x2 = T where T = 90 s and θ90 and θ180 are the temperatures at t = 90 s and t = 180 s. x2 = .............................................................. [1] (iii) Calculate the average cooling rate x3 during the last 90 s of the experiment. Use your readings from Table 2.1 and the equation θ180 – θ270 x3 = T where T = 90 s and θ180 and θ270 are the temperatures at t = 180 s and t = 270 s. x3 = .............................................................. [1] (d) (i) The temperature of the water falls as time passes. Use your results from (c) to describe the pattern of the rate of cooling of the water during the experiment. Justify your answer by reference to your results. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Give an estimate of the probable final temperature θF of the water if left to cool for many hours. θF = .............................................................. [1] (e) (i) A student in another school carries out a similar experiment. She starts with the hot water at a lower initial temperature. Suggest how her cooling rates are likely to compare with those calculated in (c). Use your results to explain your answer. suggestion ......................................................................................................................... ........................................................................................................................................... explanation ........................................................................................................................ ........................................................................................................................................... ........................................................................................................................................... [2] (ii) State one variable, other than the initial temperature, which the student should control. ........................................................................................................................................... ..................................................................................................................................... [1] [Total: 11]

Mark scheme: 2(a)(i) suitable value for θ R 1 2(a)(ii) θ decreasing and recorded to at least 1 °C 1 2(b) s, °C both correct 1 2(c)(i) correct calculation of x1 1 2(c)(ii) unit °C / s, seen in (c) and not contradicted 1 2(c)(iii) x3 < x2 < x1 1 2(d)(i) cooling rate decreases (over time) and justified by comparative values of cooling rate over suitable periods of time 1 2(d)(ii) θ F = θ R 1 Question Answer Marks 2(e)(i) suggestion matching results 1 explanation matching suggestion: EITHER: SUGGESTION: smaller cooling rates (at equivalent times) EXPLANATION: reference to cooling rate being smaller at lower temperatures and values stated OR SUGGESTION: smaller difference(s) in cooling rates (between equivalent times) EXPLANATION: clear reference to (x2 – x3) being smaller than (x1 – x2) 1 2(e)(ii) suitable control: (same) volume of water, (same) material of beaker, (same) duration of experiment, (same) room temp / named appropriate environmental condition 1

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3 In this experiment, you will investigate a power supply. The circuit has been set up for you. Carry out the following instructions, referring to Fig. 3.1. power supply V crocodile clip A l resistance wire Fig. 3.1 (a) Connect the crocodile clip to a length l = 100.0 cm of the resistance wire. Switch on. Measure the value of potential difference V0 and current I0 for the wire. V0 = .......................................................... V I0 = ........................................................... A Switch off. Calculate the resistance R0 of 100.0 cm of the wire. Use your values of V0 and I0 and the V0 equation R0 = . I0 R0 = ......................................................... Ω [1] (b) (i) Switch on. Connect the crocodile clip to lengths l = 70.0 cm, 60.0 cm, 50.0 cm, 40.0 cm and 30.0 cm of the resistance wire in turn. For each length l measure the current I in the circuit. Record your readings in Table 3.1. [1] Switch off. Table 3.1 1 1 l / cm I / A I A / 70.0 60.0 50.0 40.0 30.0 1 (ii) Calculate, and record in Table 3.1, the value of for each length l of the wire. [1] I 1 1 (c) Plot a graph of l / cm (y‑axis) against (x‑axis). You do not need to start your axes at the I A origin (0,0). / [4] (d) (i) Determine the gradient G of the graph. Show clearly on the graph how you obtained the necessary information. G = .............................................................. [1] (ii) Calculate the electromotive force (e.m.f.) E of the power supply. Use your value of R0 G × R0 from (a) and the equation E = , where k = 100 cm. k E = ........................................................... V [1] (e) The ammeter in this circuit has a small resistance which affects the current. The effect of this resistance on the measured current I will be different for each measured length l of the resistance wire. State and explain which length l will be most affected by the resistance of the ammeter. statement .................................................................................................................................. explanation ............................................................................................................................... ................................................................................................................................................... [2] [Total: 11]

Mark scheme: 3(a) and correct calculation of R0 3(b)(i) I all increasing and to 2dp at least 1 3(b)(ii) correct calculations of 1 / I 1 Question Answer Marks 3(c) 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 line 1 3(d)(i) G present and triangle method seen on graph line 1 3(d)(ii) E in range 1.0 (V) to 4.0 (V) 1 3(e) l = 30.0 cm 1 reference to ammeter forming greater proportion of total resistance 1

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4 A student investigates a wind turbine, which is an electrical generator driven by a propeller blade. Plan an experiment which will enable him to investigate how the current in a resistor connected across the terminals of the turbine varies with the speed of the air flow through the turbine. You are not required to carry out the experiment. The apparatus available includes: a model wind turbine as shown in Fig. 4.1 an electric fan to provide the moving air to turn the turbine a device for measuring air speed. In your plan, you should: • list any additional apparatus needed • complete the wind turbine circuit diagram on Fig. 4.1 • state the key variables to be kept constant • explain briefly how to carry out the experiment, including how the speed of the air flow is to be changed • explain how to use the readings to reach a conclusion. resistor wind turbine propeller blade electric fan bench Fig. 4.1 .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7] [Total: 7]

Mark scheme: 4 MP1 circuit diagram: ammeter in series with resistor and circuit correct 1 MP2 apparatus: ammeter and means of measuring candidate’s independent variable if other than air speed e.g. (metre) rule if distance is independent variable, protractor if angle of air flow is independent variable 1 MP3 control variable (one from): speed of fan (if distance / angle varied) or distance / angle between fan and turbine (if fan speed varied), height of fan / turbine, angle of air flow 1 MP4 method: measure / record independent variable (allow turbine to turn and) measure / record current, 1 MP5 repeat for different value of independent variable 1 Question Answer Marks 4 MP6 analysis: compare readings (in a table) to see if change in independent variable produces change in current / plot line graph (with correct axes specified) 1 MP7 additional point (one from): at least 5 sets of data taken, repeat each measurement and take average, 2nd valid control variable stated, repeat for different resistor and compare pattern preliminary experiment to determine suitable range for independent variable measure air speed at same point each time 1

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