Cambridge IGCSE Physics 0625 — 2023 Oct/Nov Paper 6 · Variant 3

1 Sand is a granular material composed of very small, irregularly‑shaped mineral particles. A student determines the density of sand by two methods. She uses the apparatus shown in Fig. 1.1 and Fig. 1.2. measuring cylinder sand top-pan balance bench 76 g 219 g bench Fig. 1.1 Fig. 1.2 Method 1 (a) (i) The student measures the mass of a 250 cm3 measuring cylinder, as shown in Fig. 1.1. She pours sand into the measuring cylinder and measures the mass of the measuring cylinder and sand, as shown in Fig. 1.2. Use the values shown in Fig. 1.1 and Fig. 1.2 to calculate the mass m of the sand. m = ...................................................... g [1] (ii) The student measures the volume V1 of the sand in the measuring cylinder. 108 V1 = ........................................................ cm3 Calculate a value for the density ρ1 of the sand sample. Use the values from (a)(i) and m the equation ρ1 = . Include a unit. V1 ρ1 = ......................................................... [2] Method 2 measuring cylinder water 160 sand sample 150 Fig. 1.3 (b) (i) The student pours 100 cm3 of water into the measuring cylinder containing the sample of sand. Some of the water soaks into the sand sample and she waits for the water level to become constant. Record the reading V2 of the water level in the measuring cylinder shown in Fig. 1.3. V2 = .................................................. cm3 [1] (ii) Calculate another value for the density ρ2 of the sand sample. m , where k = 100 cm3. Use the values from (a)(i) and (b)(i) and the equation ρ2 = (V 2 - k) ρ2 = ......................................................... [2] (iii) Fig. 1.4 On Fig. 1.4, draw an arrow showing the correct line of sight for reading the volume of water in the measuring cylinder. [1] (c) Another student wants to determine the density of the particles in a similar sample of sand. (i) Explain why method 1 would not be a suitable method for him to use. ........................................................................................................................................... ..................................................................................................................................... [1] (ii) Explain why method 2 would give a more accurate value for the density of the particles in this sample of sand. ........................................................................................................................................... ..................................................................................................................................... [1] (d) Describe two possible sources of inaccuracy in the measurements taken in method 1 or method 2, even if they are carried out carefully. 1 ................................................................................................................................................ ................................................................................................................................................... 2 ................................................................................................................................................ ................................................................................................................................................... [2] [Total: 11]

Mark scheme: Question Answer Marks 1(a)(i) m = 143(g) 1 1(a)(ii) 1 = 1.32 1 unit: g / cm3 1 1(b)(i) V2 = 154(cm3) 1 1(b)(ii) 2 = 2.65 1 2 and 1 to consistent 2 or consistent 3 significant figures 1 1(b)(iii) arrow or line perpendicular to scale 1 1(c)(i) Method 1 – reference to idea of volume being larger than volume of particles in sample / (idea of) gaps between the grains 1 1(c)(ii) Method 2 – water displaces air (owtte) and (calculated) volume is actually that of particles / (idea of) gaps filled with water 1 1(d) two appropriate sources of inaccuracy from: 2 sand surface not flat / top pan balance only to nearest gram / measuring cylinder graduations too large

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2 A student investigates the cooling of hot water in surroundings with different temperatures. He uses the apparatus shown in Fig. 2.1. thermometer lid beaker A beaker B bench Fig. 2.1 (a) The student pours 100 cm3 of cold water into beaker B and places the thermometer in the water. Measure, and record in the appropriate column heading of Table 2.1, the temperature θ1 of the water, as shown in Fig. 2.2. 30 20 10 Fig. 2.2 [1] (b) The student places beaker A inside beaker B as shown in Fig. 2.3 so that the water in beaker B rises between the sides of the two beakers. beaker B beaker A water Fig. 2.3 He removes the lid and pours 150 cm3 of hot water into beaker A. He replaces the lid and puts the thermometer into the hot water in beaker A. He records, in Table 2.1, the temperature θA of the water every 30 s. Describe one precaution that can be taken to ensure that the temperature readings are as accurate as possible. ................................................................................................................................................... ............................................................................................................................................. [1] (c) The student repeats the process for water at a higher temperature θ2 in beaker B. His readings are shown in Table 2.1. Table 2.1 beaker A beaker A in cold water in warm water 48 θ1 = ...................°C θ2 = ...................°C t / s θA / °C θA / °C 0 78.5 80.0 30 72.5 77.0 60 69.0 74.5 90 66.5 73.0 120 65.0 71.5 150 63.5 70.5 180 62.0 70.0 Write a conclusion stating in what way the temperature of the water surrounding beaker A affects the rate of cooling of the hot water in beaker A. Justify your answer by reference to values from the readings. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (d) Calculate the average cooling rate R for beaker A cooling in cold water. Use the readings for beaker A from Table 2.1 and the equation θA0 – θA180 R = T where T = 180 s and θA0 and θA180 are the temperatures of the water in beaker A at t = 0 and t = 180 s. Include the unit for the cooling rate. R = ......................................................... [2] (e) Another student repeats this experiment at the same room temperature. State two other variables that she controls in order to obtain readings as close as possible to the readings in Table 2.1. 1 ................................................................................................................................................ ................................................................................................................................................... 2 ................................................................................................................................................ ................................................................................................................................................... [2] (f) After 180 s, the student measures the temperature of the water surrounding beaker A in the first experiment and finds that θ1 = 49 °C. (i) State the reason why this can affect the results of the investigation and suggest what effect it has on the value of cooling rate R. reason ............................................................................................................................... ........................................................................................................................................... effect on R ......................................................................................................................... ........................................................................................................................................... [2] (ii) Suggest one change to the experiment to reduce the effect in (f)(i). ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[1] [Total: 11]

Mark scheme: 2(a) 1 = 18(°C) 1 2(b) suitable precaution e.g. 1 view scale reading perpendicularly, wait until readings stops rising (at start), avoid thermometer touching beaker 2(c) statement matching readings in table 1 comparison of temperature changes over 180 s, matching statement, need to see both 16.5 and 10 1 2(d) R = 0.092 OR 0.09 OR 0.0917 1 unit °C/s 1 2(e) Two suitable controls from: 2 volume of water, initial temperature material of beaker / thickness of beaker / surface area of beaker 2(f)(i) 1 not constant / higher than 2 at the end 1 value of R reduced / decreases / low(er) / small(er) 1 2(f)(ii) large(r) volume of water surrounding beaker A / 1 use of constant temperature water bath

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3 A student determines the focal length of a converging lens. She uses the apparatus shown in Fig. 3.1. illuminated u v screen object lens lamp bench Fig. 3.1 (a) The student sets the distance u between the illuminated object and the lens to 20.0 cm. She moves the screen until a sharp image of the illuminated object is seen on the screen. She then measures, and records in Table 3.1, the distance v between the lens and the screen. Describe a technique to obtain an image on the screen that is as sharp as possible in this experiment. Include in your description: • where the screen should be placed initially • how an accurate position for the sharp image is obtained. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ............................................................................................................................................. [2] (b) The student repeats the procedure for u = 30.0 cm, 40.0 cm, 50.0 cm and 60.0 cm. Her readings are shown in Table 3.1. Table 3.1 u u / cm v / cm v 20.0 60.0 30.0 27.3 1.10 40.0 25.8 1.55 50.0 21.4 2.34 60.0 20.0 3.00 u For distance u = 20.0 cm, calculate, and record in Table 3.1, the value of v. [1] u(c) Plot a graph of u / cm (y‑axis) against (x‑axis). Start your graph at the origin (0,0). v Draw the best‑fit line. 0 0 [4] u(d) (i) Determine the value u0 of u when = 0. v u0 = ......................................................... [1] (ii) The gradient of the graph is numerically equal to the focal length f of the lens. Determine the value of f for this experiment. Show clearly on the graph how you obtained the necessary information to determine the gradient. f = ......................................................... [2] (e) Suggest one precaution that can be taken to ensure measurements are accurate in this experiment. ................................................................................................................................................... ............................................................................................................................................. [1] [Total: 11]

Mark scheme: 3(a) move screen slowly 1 backwards and forwards 1 3(b) u / v = 0.33 1 3(c) graph: 1 • axes labelled with quantity and unit • 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) u0 in range 13 to 18(cm) 1 triangle method seen on graph 1 3(d)(ii) f to 2 or 3 significant figures with unit – cm 1 3(e) mark base of lens/ 1 clamp rule to bench/ lens and screen upright/ darkened room

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4 A student investigates the brightness of a lamp. Plan an experiment to investigate how the intensity (brightness) of the light produced by the lamp is affected by the current in the lamp. The apparatus available includes: • a lamp and power supply • a light meter which measures the intensity of light arriving at it • an ammeter • a variable resistor. In your plan, you should: • complete the circuit diagram in Fig. 4.1 to show the variable resistor connected to control the current in the lamp • state the key variables to be kept constant • explain briefly how to do the experiment • draw a table with column headings, to show how to display the readings (you are not required to enter any readings in the table) • explain how to use the readings to reach a conclusion. A light meter Fig. 4.1 .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .................................................................................................................................................... [7]

Mark scheme: 4 MP1 apparatus: 1 correct variable resistor symbol in series MP2 method: 1 measure current OR measure AMPS measure light intensity MP3 repeat for different current OR different resistance 1 MP4 control variable (one from): 1 ambient light level OWTTE distance from lamp to light meter MP5 table: 1 columns for current (with unit) and light intensity MP6 analysis: 1 compare readings in a table to see if change in current produces change in light intensity/ plot line graph with axes specified or draw labelled axes MP7 additional point (one from): 1 at least 5 sets of data taken, repeat each measurement and take average, 2nd control variable stated, Additional graph notes: NOTE: – The principle to apply here is ‘could I draw a significantly better line, using these points, under examination conditions?’ If the answer is definitely ‘yes’, do not award the mark. NOTE: – If candidate’s scale consists of actual readings at equal intervals this will produce a perfect straight line! The only marks available in this case are the first (axes right way round and labelled) So maximum 1. If axes are wrong way round, the other 3 marks are still available.

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