Cambridge A Level Physics 9702 — 2013 May/June Paper 3 · Variant 2

1 In this experiment, you will investigate the time for the voltage across a component to Use decrease after a switch is opened. You have been provided with a circuit containing a power supply, switch and a component C, as shown in Fig. 1.1. Throughout the experiment do not disconnect this circuit. d.c. supply + – C Fig. 1.1 (a) Assemble the circuit of Fig. 1.2 with the 10.0 kΩ resistor clipped into the component holder as resistance S. d.c. supply + – C + V X S component holder Fig. 1.2 (b) (i) Close the switch and check that the voltmeter reading is between 4 V and 8 V. For Examiner’s (ii) When the switch is opened the voltmeter reading will gradually decrease. Use Take measurements to find the time t for the voltmeter reading to decrease to 2.0 V after the switch is opened. Record t. t = ..................................................[2] (c) Repeat (b) with different resistors in the component holder until you have six sets of For values of S and t. Examiner’s 1 1 Use Include values of and in your table. S t [10] 1 1 (d) (i) Plot a graph of on the y-axis against on the x-axis. [3] t S (ii) Draw the straight line of best fit. [1] (iii) Determine the gradient and y-intercept of this line. gradient = ....................................................... y-intercept = ...................................................... [2] For Examiner’s Use (e) The quantities t and S are related by the equation For Examiner’s 1 a Use = + ab t S where a and b are constants. Using your answers from (d)(iii), determine the values of a and b. Give appropriate units. a = ....................................................... b = ....................................................... [2] Please turn over for Question 2. You may not need to use all of the materials provided. For Examiner’s

Mark scheme: 1 (b) (ii) Value of t in the range 10.0 s ≤ t ≤ 20.0 s. [1] Evidence of repeat measurements of t. [1] (c) Six sets of readings of S and t scores 5 marks, five sets scores 4 marks etc. [5] If trend wrong or no S or t column –1. Major help from Supervisor –2 (setting up circuit). Minor help from Supervisor –1. Range: [1] Values of S must include 22 (kΩ) or 10 (kΩ) and 1.2 (kΩ) or 1.0 (kΩ). Column headings: [1] Each column heading must contain a quantity and a unit. The presentation of quantity and unit must conform to accepted scientific convention e.g. 1/t / s–1 1/S / kΩ –1 1/S (kΩ –1) t / s t (s). ( 1/t(s) 1/S 1/kΩ 1/S (kΩ) –1 are not allowed.) Consistency: [1] All values of raw t must be given to the same precision (either 0.1 s or 0.01 s). Significant figures: [1] Significant figures for every row of values of 1/S must be the same as or one greater than the s.f. in S as recorded in table. Calculation: [1] Values of 1/t calculated correctly. (d) (i) Axes: [1] Sensible scales must be used, no awkward scales (e.g. 3:10). Scales must be chosen so that the plotted points occupy at least half the graph grid in both x and y directions. Scales must be labelled with the quantity that is being plotted. Scale markings should be no more than three large squares apart. Plotting of points: [1] All observations in the table must be plotted. Points must be plotted to an accuracy of half a small square. Diameter of points must be ≤ half a small square (no “blobs”). Quality: [1] All points in the table must be plotted (at least 5) for this mark to be awarded. Judge by the scatter of all the points about the straight line. Points must be less than 0.05 kΩ ─1 from a straight line on the 1/S axis. (ii) Line of best fit: [1] Judge by balance of all points on the grid about the candidate’s line (at least 5 points). There must be an even distribution of points either side of the line along the full length. Allow one anomalous point only if clearly indicated (i.e. circled or labelled) by the candidate. Line must not be kinked or thicker than half a small square. GCE AS/A LEVEL – May/June 2013 9702 32 (iii) Gradient: [1] The hypotenuse of the triangle must be at least half the length of the drawn line. Both read-offs must be accurate to half a small square in both the x and y directions. The method of calculation must be correct. y-intercept: [1] Either: Correct read-off from a point on the line substituted into y = mx + c. Read-off must be accurate to half a small square in both x and y directions. Or: Intercept read off directly from the graph. (e) Value of a = candidate’s gradient. Value of b = candidate’s intercept / candidate’s gradient = candidate’s intercept / a [1] Unit for a correct and consistent with value e.g. kΩ s–1, Ω s–1. [1] [Total: 20]

More questions on Practical circuits

2 In this experiment, you will investigate the relationship between the volume of a bubble of air Use in water and the diameter of the tube that produces it. (a) You are provided with a syringe connected to a length of plastic tube which has a smaller tube sealed into its end with Blu-Tack. (i) Take measurements to determine the internal diameter d of the smaller tube. d = ..................................................[2] (ii) Estimate the percentage uncertainty in your value of d. percentage uncertainty = ..................................................[1] (b) (i) Position the plunger at the 5 ml mark on the syringe. Check that there is no water in the syringe or tube. (ii) Immerse the end of the tube approximately 2 cm below the surface of the water in the beaker, as shown in Fig. 2.1. syringe plunger tube 2 cm smaller tube beaker Blu-Tack water Fig. 2.1 (c) (i) Slowly push in the syringe plunger until it is just past the 4 ml mark on the syringe For barrel. Examiner’s Record the reading r1 from the syringe. (Note that 1 ml = 1 cm3.) Use r1 = ...........................................cm3 [1] (ii) Count the number n of bubbles that are produced as you slowly push in the plunger until it is just past the 2 ml mark. Record n and the new reading r2 from the syringe. n = ..................................................[1] r2 = ............................................... cm3 (iii) Calculate the average volume V of air in a single bubble using the relationship r1 – r2 V = . n V = .......................................... cm3 [1] (d) Justify the number of significant figures you have given for your value of V. .......................................................................................................................................... .......................................................................................................................................... ......................................................................................................................................[1] (e) (i) Take the tube out of the beaker and remove the smaller tube and Blu-Tack from the For end. Examiner’s Use (ii) Take measurements to determine the internal diameter d of the length of tube still attached to the syringe. d = ..................................................[1] (iii) Repeat steps (b) and (c). r1 = ................................................cm3 n = ...................................................... r2 = ................................................cm3 V = ................................................cm3 [2] (f) It is suggested that the relationship between V and d is V 3 = k d 2 where k is a constant. (i) Using your data, calculate two values of k. first value of k = ...................................................... second value of k = ...................................................... [1]

Mark scheme: 2 (a) (i) Measurement of d with unit in range 0.5 mm – 2.5 mm. [1] Evidence of repeated readings of d. [1] (ii) Absolute uncertainty in d in the range 0.2 – 0.5 mm. [1] If repeated readings have been taken, then the absolute uncertainty can be half the range (but not zero if values are equal). Correct method of calculation to get percentage uncertainty. (c) (i) Measurement of r1 recorded to nearest 0.1 cm3, and in range 1 to 5 cm3. [1] (ii) Value for n. [1] (iii) Correct calculation of V. [1] (d) Justification of s.f. in V linked to significant figures in (r1 – r2) and in n. [1] (e) (ii) Second value of d. [1] (iii) Second value of n. [1] Quality: V larger for larger d. [1] (f) (i) Two values of k calculated correctly. [1] (ii) Sensible comment relating to the calculated values of k, testing against a criterion specified by the candidate. [1] GCE AS/A LEVEL – May/June 2013 9702 32 (g) (i) Limitations 4 max. (ii) Improvements 4 max. Do not credit A two readings not enough (to draw a take many readings and plot a repeat readings/few conclusion) graph/take many readings and readings/take more calculate more k values and readings and compare (calculate) average k/only one reading

More questions on Physical quantities