Cambridge A Level Physics 9702 — 2017 Oct/Nov Paper 3 · Variant 6

1 In this experiment, you will investigate the oscillations of a wire shape. (a) Measure and record the length L of the wire shape, as shown in Fig. 1.1. L wire Fig. 1.1 L = ............................................. cm (b) (i) Assemble the apparatus as shown in Fig. 1.2. The rods of the clamps should be parallel to each other and at the same height above the bench. The wire shape should be placed centrally on the rods. Adjust the apparatus so that the distance between the centres of the rods is approximately 22 cm. rod of wire clamp boss stand bench FRONT VIEW jaw of clamp stand wire x TOP VIEW Fig. 1.2 (ii) The distance between the centres of the rods is x. Measure and record x. x = ............................................. cm (c) (i) Push the centre of the wire a small distance away from you. Release it so that it oscillates. (ii) Take measurements to determine the period T of the oscillations. T = .............................................. [2] L(d) For values of x less than , the wire shape inverts as shown in Fig. 1.3. 2 Fig. 1.3 L Calculate . 2 L = ............................................. cm 2 L(e) Vary x in the range < x < 24 cm. Repeat (b)(ii) and (c) until you have six sets of 2 values of x and T. Record your results in a table. Include your values from (b)(ii) and (c). Also include L 1 - values of x and 2 in your table. c 2 m T [10] 1 L - on the x-axis. [3](f) (i) Plot a graph of 2 on the y-axis against x T c 2 m (ii) Draw the straight line of best fit. [1] (iii) Determine the gradient and y-intercept of this line. gradient = ................................................... y-intercept = ................................................... [2] (g) It is suggested that the quantities T and x are related by the equation 1 L - + b 2 = a x T c 2 m where a and b are constants. Using your answers in (f)(iii), determine the values of a and b. Give appropriate units. a = ................................................... b = ................................................... [2] [Total: 20] You may not need to use all of the materials provided.

Mark scheme: 1(c)(ii) T with unit in range 0.1–1.0 s. 1 Evidence of repeated readings of nT where n = 5 or more. 1 1(e) Six sets of readings of x and T showing the correct trend and without help from the Supervisor scores 5 marks, five sets scores 4 marks etc. 5 Range: 0 ⩽ (x – L / 2)min ⩽ 1.0 cm. 1 Column headings: Each column heading must contain a quantity and a unit where appropriate. The presentation of quantity and unit must conform to accepted scientific convention. e.g. 1/T2 / s–2. 1 Consistency: All values of x must be given to the nearest mm. 1 Significant figures: Significant figures for every value of 1 / T2 same as, or one greater than, the s.f. of raw time as recorded in table. If raw times recorded to nearest 0.01 s, allow number of significant figures of 1 / T2 to be one less than the number of significant figures of the raw times. 1 Values of (x – L / 2) calculated correctly. 1 Question Answer Marks 1(f)(i) Axes: Sensible scales must be used, no awkward scales (e.g. 3:10 or fractions). 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. 1 Plotting of points: All observations must be plotted on the grid. Diameter of plotted points must be ⩽ half a small square (no “blobs”). Points must be accurate to within half a small square in both x and y directions. 1 Quality: All points in the table must be plotted (at least 5) for this mark to be awarded. Scatter of points must be no more than ± 0.25 cm from a straight line in the (x – L / 2) direction. 1 1(f)(ii) Line of best fit: Judged 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 point only if clearly indicated (i.e. circled or labelled) by the candidate. Lines must not be kinked or thicker than half a square. 1 1(f)(iii) Gradient: The hypotenuse of the triangle used must be greater than half the length of the drawn line. The method of calculation must be correct. Both read-offs must be accurate to half a small square in both the x and y directions. 1 y-intercept: 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 directly from the graph, with read-off at x = 0, accurate to half a small square in the y direction. 1 1(g) Value of a = candidate’s gradient and value of b = candidate’s intercept. The values must not be fractions. 1 Unit for a correct (e.g. cm–1s–2) and unit for b correct (e.g. s–2). 1

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2 In this experiment, you will investigate how the deflection of a wooden strip depends on the distribution of the load on the strip. (a) (i) Lay the wooden strip flat on the bench. Place the ten slotted masses along the strip, as shown in Fig. 2.1. centre line wooden position masses position strip of mark of mark Fig. 2.1 (ii) Using the pen, make a small mark on the edge of the strip at each end of the row of masses, as shown in Fig. 2.1. (iii) Remove the masses. (iv) Measure and record the distance D between the marks, as shown in Fig. 2.2. mark mark D Fig. 2.2 D = .............................................. [1] (b) (i) Place the strip on the two wooden blocks with the inner edges of the blocks at the marks, as shown in Fig. 2.3. centre wooden mark strip mark line block h1 bench Fig. 2.3 (ii) Measure and record the height h1 of the bottom of the strip at the centre line, as shown in Fig. 2.3. h1 = .............................................. [1] (c) Estimate the percentage uncertainty in your value of h1. percentage uncertainty = .............................................. [1] (d) (i) Replace the masses on the strip and ensure the blocks are still positioned at the marks. Measure and record the height h2 of the bottom of the strip at the centre line, as shown in Fig. 2.4. h2 Fig. 2.4 h2 = ................................................... (ii) Calculate d, where d = h1 – h2. d = .............................................. [1] (e) (i) Remove the masses from the strip. (ii) Ensure the blocks are still positioned at the marks. Measure and record the height h3 of the bottom of the strip at the centre line. h3 = ................................................... (iii) Place all the masses at the centre line, as shown in Fig. 2.5. h4 Fig. 2.5 (iv) Ensure the blocks are still positioned at the marks, then measure and record the height h4 of the bottom of the strip at the centre line. h4 = ................................................... (v) Calculate p, where p = h3 – h4. p = ...................................................

Mark scheme: 2(a)(iv) Value of D with unit to nearest mm and in range 10.0–150.0 cm. 1 2(b)(ii) Value of h1 with consistent unit and in range 6.0–10.0 cm. 1 2(c) Absolute uncertainty in h1 of 1 mm and correct method of calculation to obtain percentage uncertainty. If repeated readings have been taken, then the uncertainty can be half the range (but not zero) if the working is clearly shown. 1 2(d)(ii) Correct calculation of d. 1 2(f)(ii) Values of t and w to nearest mm, with unit. 1 2(f)(iii) Correct calculation of E. 1 2(g) Second values of h1 and h2. 1 Quality: Second value of d < first value of d. 1 Second values of h3 and h4. 1 2(h)(i) Two values of k calculated correctly. 1 2(h)(ii) Justification for s.f. in k linked to s.f. in d and p, or linked to s.f. in h1, h2, h3 and h4. 1 2(h)(iii) Valid comment relating to the calculated values of k, testing against a criterion stated by the candidate. 1 Question Answer Marks 2(i)(i) A Two readings/too few readings/only two readings not enough to draw a (valid) conclusion. B Difficult to pile masses in centre, with reason. C Blocks move/slip/tilt. D d (or p or t) small so large uncertainty/ large % uncertainty in d (or p or t). E Permanent deformation of strip. F Difficult to mark ends of D due to curvature of masses. 1 mark for each point up to a maximum of 4. 4 2(i)(ii) A Take more readings and plot a graph/calculate more k values and compare. B Improved method for point load, e.g. suspend masses below strip/named method for sticking masses together. C Named means of stabilising blocks, e.g. stick to bench/stick to strip/stops on bench/clamp blocks to bench. D Use calipers or travelling microscope or use micrometer for t value or measure stack of MDF pieces. E Use 8 masses before 10 or turn strip over. F Use set square with detail/measure length of 10 masses then mark strip. 1 mark for each point up to a maximum of 4. 4

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