Cambridge IGCSE Physics 0625 — 2016 Oct/Nov Paper 6 · Variant 3

1 Some students are investigating how the surface area of water exposed to the air affects the rate at which the water cools. They are using the apparatus shown in Fig. 1.1. Beaker B is bigger than beaker A. °C °C 110 110 100 100 90 90 80 80 70 70 water surface 60 60 50 50 hot water 40 40 30 30 20 20 10 10 0 0 –10–10 –10 A B Fig. 1.1 (a) The students pour 75 cm3 of hot water into beaker A and 75 cm3 of hot water into beaker B. They immediately start a stopclock. (i) Record, in the first row of Table 1.1, the initial temperatures θ of the water in beaker A and in beaker B, as shown in Fig. 1.1. [1] (ii) The students record the temperatures θ of the water every 30 s. Their readings are shown in Table 1.1. Complete the headings and the time t column in Table 1.1. [2] Table 1.1 beaker A beaker B t / θ/ θ/ 0 80.0 76.0 78.0 73.5 76.5 71.0 75.0 68.5 73.5 66.5 72.5 65.0 (b) Describe two precautions which should be taken, when using this apparatus, to ensure that the temperature readings are as reliable as possible in the experiment. 1. ............................................................................................................................................... ................................................................................................................................................... 2. ............................................................................................................................................... ................................................................................................................................................... [2] (c) (i) Write a conclusion, stating how increasing the surface area of the hot water affects the rate of cooling of the water. Justify your answer by reference to the results. ........................................................................................................................................... ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[2] (ii) Suggest a change to the apparatus to make the comparison of the effect of surface area on cooling a fairer test. Explain why the change is an improvement and state the likely effect on the recorded temperatures. change .............................................................................................................................. ........................................................................................................................................... explanation ........................................................................................................................ ........................................................................................................................................... effect on temperatures ...................................................................................................... ........................................................................................................................................... [3] (d) Students in other classrooms are carrying out the same experiment. Suggest a factor that they should keep the same if they are all to obtain similar temperature readings. ................................................................................................................................................... ...............................................................................................................................................[1] [Total: 11]

Mark scheme: 1(a)(i) 1 1(a)(ii) units all correct (symbols or words) t values all present (30, 60, 90, 120, 150 and 180) 1 1 1(b) any 2 appropriate precautions: e.g. viewing perp. to thermometer scale (to avoid parallax) stir before reading keep thermometer at same level / not touching beaker walls wait until reading stops rising at the start 2 1(c)(i) Conclusion and explicit quoting of figures from the table which relate to the whole 180 s period (eg 15.0 and 9.5 °C, or 5.5 °C more) statement that B cools more quickly / its temperature drops faster / its temperature falls more in the same time 1 1 1(c)(ii) any suitable improvement to apparatus relating to comparison: e.g. insulate sides, use plastic beaker, stand on mat matching explanation: e.g. thermal energy only escapes from surface, surface area only variable changed, less transfer of thermal energy / heat by sides appropriate effect on values of θ: e.g. all higher 1 1 1 Question Answer Mark 1(d) any appropriate factor: e.g. volume of water, initial temperature of water, similar ratio of surface areas, type / material / size of beaker, room temperature 1 Total 11

More questions on Transfer of thermal energy

2 Some students are determining the focal length of a converging lens by two different methods. They are using the apparatus shown in Fig. 2.1. illuminated triangle screen u lens Fig. 2.1 (a) A student sets the distance u between the illuminated triangle and the lens to 20.0 cm. She moves the screen until a sharp image of the triangle is seen on the screen. (i) • Measure ho, the height of the illuminated triangle, as shown in Fig. 2.2. ho = ............................................................... • Measure hI, the height of the image on the screen, as shown in Fig. 2.3. hI = ............................................................... [2] h I ho Fig. 2.2 Fig. 2.3 hI (ii) Calculate a value M for the magnification, using the equation M = . ho M = ...........................................................[1] u M (iii) Calculate a value for the focal length f1 of the lens, using the equation f1 = , (M + 1) where u = 20.0 cm. f1 = ...........................................................[2] (iv) Describe one difficulty that might be experienced when measuring the height of the image. Suggest an improvement to the apparatus to overcome this. difficulty ............................................................................................................................. ........................................................................................................................................... improvement ...................................................................................................................... ........................................................................................................................................... [2] (b) The student adjusts the position of the lens so that u = 40.0 cm. She moves the screen until a sharp image of the triangle is again seen on the screen. Fig. 2.4 is a scale diagram showing her result. illuminated screen triangle lens Fig. 2.4 (i) • On Fig. 2.4, measure the distance between the lens and the screen. distance = ............................................................... • Fig. 2.4 is drawn to 1/5th scale. Determine the actual distance v between the lens and the screen in the experiment. v = ............................................................... [1] (ii) • Calculate a second value f2 for the focal length of the lens, using the equation u v f2 = , where u = 40.0 cm. (u + v ) f2 = ............................................................... • The student suggests that f1 and f2 should be equal. State whether the results support this suggestion. Justify your statement with reference to the results. .................................................................................................................................... .................................................................................................................................... .................................................................................................................................... [2] (c) State one precaution, not included in your answer to (a)(iv), that you would take to make the experiment reliable. ................................................................................................................................................... ...............................................................................................................................................[1] [Total: 11]

Mark scheme: 2(a)(i) hO = 1.5 (cm) hI = 4.0 (cm) 1 1 2(a)(ii) M = 2.7 (or ecf) and no unit for M 1 2(a)(iii) Answer given to 2 / 3 sig figs and with appropriate unit Value given for f1 rounds to 14.5 or 14.6 (cm) 1 1 2(a)(iv) any appropriate difficulty: e.g. hand / ruler in way of image matching improvement: e.g. use translucent screen and view from behind use transparent ruler, fix ruler / grid to screen 1 1 2(b)(i) distance present, and v = 25(.0) (cm) 1 2(b)(ii) f2 present (expect 15.4 (cm)) and statement matching results justification matching correct statement (‘within limits of experimental accuracy’ / owtte) 1 1 2(c) any suitable precaution: e.g. dark room / bright light (centre of) lens and object same height (above bench), lens / object / screen perpendicular (any one will suffice), ruler fixed / placed on bench, mark centre of lens on holder repeat with different values of u / different sizes of object 1 Total 11

More questions on Light

3 A student is investigating the resistance of a lamp. He is using the circuit shown in Fig. 3.1. power supply slide wire A crocodile clip V Fig. 3.1 (a) The student connects the crocodile clip on the slide wire to give particular values of the potential difference V across the lamp. He measures the current I in the lamp for each position. Figs. 3.2 to 3.6 show the ammeter readings for values of V = 0.5 V, 1.0 V, 1.5 V, 2.0 V and 2.5 V, respectively. Read, and record in Table 3.1, the value of I for each value of potential difference V. Record each value to 2 significant figures. 0.2 0.3 0.2 0.3 0.2 0.3 0.1 0.4 0.1 0.4 0.1 0.4 A A A 0 0.5 0 0.5 0 0.5 Fig. 3.2 Fig. 3.3 Fig. 3.4 0.2 0.3 0.2 0.3 0.1 0.4 0.1 0.4 A A 0 0.5 0 0.5 Fig. 3.5 Fig. 3.6 [2] (b) Calculate, and record in Table 3.1, the resistance R of the lamp at each value of V. V Use the equation R = . I [1] Table 3.1 V / V I / A R / Ω 0.5 1.0 1.5 2.0 2.5 (c) Plot a graph of R / Ω (y-axis) against V / V (x-axis). [4] (d) State what the shape of the graph tells you about the change, if any, in the resistance of the lamp during the experiment. ................................................................................................................................................... ................................................................................................................................................... ................................................................................................................................................... ...............................................................................................................................................[2] (e) In this type of experiment, it is possible to change the current and potential difference for the lamp by using a variable resistor rather than a slide wire. On Fig. 3.7, complete the circuit diagram to show a variable resistor used for this purpose. power supply A V Fig. 3.7 [2] [Total: 11]

Mark scheme: 3(a) Four correct I values (0.12, 0.15, 0.17, 0.19 and 0.21) present The fifth one is also correct 1 1 3(b) correct calculations of R (4.2, 6.7, 8.8, 10.5, 11.9) or ecf from (a) 1 3(c) graph: axes correct way round, labelled with quantity and unit appropriate scales (plots occupying at least ½ grid) plots all correct to ½ small square well-judged line and thin line, precise plots 1 1 1 1 3(d) simple statement matching candidate’s line (e.g. resistance increases with p.d.) qualified (e.g. changes less rapidly for greater p.d. values) 1 1 3(e) correct symbol for variable resistor (rectangle with strike-through arrow only) in correct series circuit 1 1 Total 11

More questions on Electrical quantities

4 A student has noticed that different types of paper have different strengths. Plan an experiment which will enable you to compare the strengths of different samples of thin paper, prepared as shown in Fig. 4.1. wooden block adhesive tape thin paper hook Fig. 4.1 Write a plan for the experiment, including: • the additional apparatus needed • instructions for carrying out the experiment, including any precautions you will take • what you will measure • how you will present your results • how you will determine which paper is the strongest • the variables you will keep the same to ensure the comparison is a fair test. You may draw a diagram if it helps to explain your plan. .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... .......................................................................................................................................................... ..................................................................................................................................................... [7] [Total: 7]

Mark scheme: 4 apparatus – workable arrangement how applied force is measured suitable table for results / plot a bar graph how to conclude which is strongest one suitable control variable: e.g. same width of sample same thickness / weight / length of paper all samples fixed in same way any 2 from: 2nd control variable, force applied smoothly / no jerking ensure no tears before applying force repeat for each type of sample / repeat with samples of different widths soft mat under weights (to cushion fall) / clamp stand to bench add weight of lower block to value of load any other suitable precaution 1 1 1 1 1 2 Total 7

More questions on Physical quantities and measurement techniques