Cambridge A Level Physics 9702 — 2014 Oct/Nov Paper 3 · Variant 1

1 In this experiment, you will investigate the motion of a system of masses. (a) Set up the apparatus as shown in Fig. 1.1, with the shorter length of string above the central loop and the longer length of string below the central loop. Place four slotted masses in the bottom loop and four slotted masses in the central loop. rod of clamp shorter length of string boss four slotted masses in the central loop longer length of string stand four slotted masses in the bottom loop bench Fig. 1.1 (b) Move the slotted masses in the bottom loop to the left. Release the slotted masses and watch the movement. The slotted masses will move to the right and then to the left again, completing a swing as shown in Fig. 1.2. one complete swing Fig. 1.2 Measure and record the time for at least 10 complete swings. Record enough readings to determine an accurate value for the time T taken for one complete swing. T = ..................................................[2] (c) Change the number of slotted masses in each loop. Use all the eight slotted masses. (i) Count and record the number B of slotted masses in the bottom loop. B = ...................................................... (ii) Count and record the number C of slotted masses in the central loop. C = ...................................................... (iii) Repeat (b). T = ...................................................... (d) Repeat (c) until you have six sets of values of B, C and T. Include your results from (b) and (c). For each set of values, use all eight slotted masses. T 2 C Include values of and in your table. B B [10] T 2 C (e) (i) Plot a graph of on the y-axis against on the x-axis. [3] B B (ii) Draw the straight line of best fit. [1] (iii) Determine the gradient and y-intercept of this line. gradient = ...................................................... y-intercept = ...................................................... [2] (f) The quantities T, B and C are related by the equation T 2 F C = + G B B where F and G are constants. Use your answers in (e)(iii) to determine the values of F and G. Give appropriate units. F = ...................................................... G = ...................................................... [2] You may not need to use all of the materials provided.

Mark scheme: 1 (b) Value of T in the range 1.1 s – 1.5 s with unit. [1] Evidence of repeated timings. [1] (d) Six sets of readings of B and C and time scores 5 marks, five sets scores 4 marks etc. [5] Incorrect trend –1. Help from Supervisor –1. Range: [1] B = 1 – 7 (or 8) and B + C = 8. Column headings: [1] Each column heading must contain a quantity and a unit where appropriate. The unit must conform to accepted scientific convention e.g. T2/B / s2, and C / B must not have a unit. Consistency: [1] All values of t must be given to either the nearest 0.1 s or 0.01 s. Significant figures: [1] All values of T2 / B must be given to the same s.f. as (or one more than) the s.f. in raw t. Calculation: [1] Values of T2 / B are calculated correctly. (e) (i) Axes: [1] Sensible scales must be used. Awkward scales (e.g. 3:10) are not allowed. 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 must be no more than three large squares apart. Plotting: [1] All observations in the table must be plotted on the graph grid, except B = 0. Diameter of plots must be ≤ half a small square (no “blobs”). Plotted points must be accurate to within half a small square. Quality: [1] All points in the table must be plotted (at least 5) for this mark to be awarded. Judge by scatter of all points about a straight line. All points must be less than ± 0.05 s2 in the T2/B direction from a straight line. (ii) Line of best fit: [1] Judge by balance of all points on the grid (at least 5) about the candidate’s line. There must be an even distribution of points either side of the line along the full length. Allow one anomalous plot only if clearly indicated by the candidate (i.e. circled or labelled). Lines must not be kinked or thicker than half a small square. (iii) Gradient: [1] Sign of gradient must match graph (expect a positive gradient). The hypotenuse of the triangle must be greater than half the length of the drawn line. Both read-offs must be accurate to half a small square in both x and y directions. The method of calculation must be correct. y-intercept: [1] Either: Correct read-offs from a point on the line and substituted into y = mx + c. Read-offs must be accurate to half a small square in both x and y directions. Or: Correct read-off of the intercept directly from the graph. (f) Value of F = candidate’s gradient. Value of G = candidate’s intercept. [1] Do not allow a value presented as a fraction. Unit for F (s2) and G (s2) correct. [1] [Total: 20]

More questions on Physical quantities

2 In this experiment, you will investigate how the number of turns of wire around a rod depends on the diameter of the wire. (a) You have been provided with a wooden rod and two lengths of wire. (i) Measure and record the diameter D of the rod as shown in Fig. 2.1. D Fig. 2.1 D = ..................................................[1] (ii) Measure and record the diameter d of the thinner wire. d = ..................................................[1] d (iii) Calculate D + . 2 d D + = ..................................................[1] 2 (b) (i) Cut the thinner wire so that its length is exactly 50.0 cm. (ii) Wrap the thinner wire around the rod. Count and record the number (n + t ) of turns of wire around the rod, where n is the number of complete turns and t is your estimate of the remaining part of a turn. (n + t ) = ..................................................[2] (iii) Estimate the percentage uncertainty in your value of (n + t ). percentage uncertainty = ..................................................[1] (c) Repeat (a)(ii), (a)(iii), (b)(i) and (b)(ii) for the thicker wire. d = ...................................................... d D + = ...................................................... 2 (n + t ) = ...................................................... [3] (d) It is suggested that the relationship between (n + t ), d and D is k (n + t ) = d 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] (ii) Justify the number of significant figures that you have given for your values of k. .................................................................................................................................. .................................................................................................................................. ..............................................................................................................................[1] (iii) Explain whether your results in (d)(i) support the suggested relationship. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. ..............................................................................................................................[1]

Mark scheme: 2 (a) (i) Value of D with unit in range 6.0 ≤ D ≤ 10.0 mm. [1] (ii) Value of d with unit to the nearest 0.01 or 0.001 mm in the range 0.14 to 0.16 mm. [1] (iii) Correct calculation of (D + d / 2). [1] (b) (ii) Value of (n + t): Whole number [1] Representation of part of a turn as a decimal or as a fraction [1] (iii) Absolute uncertainty of twenty-fifth of turn ≤ uncertainty in (n + t) ≤ quarter of a turn. If repeated readings have been taken, then the uncertainty can be half the range (but not zero) if the working is clearly shown. Correct method of calculation to get percentage uncertainty. [1] (c) Second value of d. Evidence of repeated readings here or in (a)(ii) [1] Second value of (n + t). [1] Second value of (n + t) ˂ first value of (n + t). [1] (d) (i) Correct calculation of two values of k. [1] (ii) Justification of s.f. in k linked to raw data in D, d and (n + t). [1] (iii) Valid conclusion based on the calculated values of k, testing against a stated criterion. [1] (e) (i) Limitations (4 max.) (ii) Improvements (4 max.) Do not credit A Two readings not enough to draw a Take many readings (for repeat readings / few conclusion. different diameters) and plot a readings graph / compare k values. B Difficult to judge fractions of a turn Improved method to measure the fraction of a turn e.g. have appropriate markings on rod. e.g. measure spare length and work out as a fraction of the circumference of the rod. e.g. 50 / circumference. C Wire slips from start Method to prevent wire moving Wire unstable position / springs away from rod. e.g. tape / Blu-tack / attach weight / clamp wire on rod. D Length not exactly 50 cm with Method to straighten wire reason e.g. kinks e.g. apply load or improved method to cut e.g. use tape and knife or use thinner wire for second wire E Thicker wire occupies a longer part Improved method of placing of the rod so there are fewer turns close together turns / angle of turn of wire affects e.g. use motor to turn rod. (n + t) / difficult to make turns touch along the rod F The values of (n + t) are close Use a thinner rod. together. [Total: 20]

More questions on Physical quantities