Cambridge A Level Physics 9702 — 2018 May/June Paper 3 · Variant 5

1 In this experiment, you will investigate the equilibrium of a metre rule. (a) (i) You have been provided with some masses. Set up the apparatus as shown in Fig. 1.1. boss rod of clamp 50 cm string loop metre rule x y string loop z string loop mass P mass Q stand bench Fig. 1.1 • Mass Q should be 200 g. • The distance between the 50 cm mark on the rule and the string loop supporting the rule is x. Adjust the position of the metre rule so that x is approximately 15 cm. • The distance between the string loop supporting mass P and the string loop supporting the rule is z. Adjust the position of mass P so that z is approximately 30 cm. • The distance between the string loop supporting the rule and the string loop supporting mass Q is y. Adjust the position of mass Q until the rule is balanced. • Measure and record z. z = .......................................................... [1] (ii) • Measure and record x. x = ............................................................... • Measure and record y. y = ............................................................... [1] (b) • Write down your value of z from (a)(i). z = ............................................................... • Keeping z constant, change x and adjust y until the rule is balanced. Repeat until you have six sets of values of x and y. Record your results in a table. You may include readings where x is measured to the left of the 50 cm mark. In such cases x has a negative value. [8] (c) (i) Plot a graph of y on the y-axis against x on the x-axis. [3] (ii) Draw the straight line of best fit. [1] (iii) Determine the gradient and y-intercept of this line. gradient = ............................................................... y-intercept = ............................................................... [2] (d) It is suggested that the quantities y and x are related by the equation y = Ax + B where A and B are constants. Using your answers in (c)(iii), determine the values of A and B. Give appropriate units. A = ............................................................... B = ............................................................... [2] (e) The mass of P is p. The mass of Q is q, where q = 0.200 kg. The constants A and B are related to p, q and z by p pz A = and B = . q q Calculate p. p = ..................................................... kg [1] (f) The experiment is repeated using the same equipment but a smaller value of z. For this experiment, draw a second line on the graph to show the expected results. Label this line W. [1] [Total: 20] You may not need to use all of the materials provided.

Mark scheme: 1(a)(i) Value of z in the range 29.0–31.0 cm to the nearest mm with unit. 1 1(a)(ii) Value of y with unit and y ⩽ 35.0 cm. 1 1(b) Six sets of readings of x and y (different values) showing the correct trend and without help from the Supervisor scores 5 marks, five sets scores 4 marks etc. 5 Range: values of x must include at least one negative value. 1 Column headings: Each column heading must contain a quantity and a unit where appropriate. The presentation of the quantity and unit must conform to accepted scientific convention e.g. x / m. 1 Consistency: All raw values of x and y must be given to the nearest mm. 1 1(c)(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 in the table must be plotted on the grid. Diameter of plotted point must be ⩽ half a small square (no “blobs”). All points must be plotted to an accuracy of half a small square. 1 Quality: All points in the table must be plotted on the grid for this mark to be awarded. It must be possible to draw a straight line that is within 1.0 cm (to scale) on the y-axis of all plotted points. 1 1(c)(ii) Line of best fit: 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 by the candidate. Line must not be kinked or thicker than half a small square. 1 Question Answer Marks 1(c)(iii) Gradient: The hypotenuse of the triangle used should be greater than half the length of the drawn line. The method of calculation must be correct. Do not allow ∆x / ∆y. Both read-offs must be accurate to half a small square in both the x and y directions. Sign of gradient must match graph. 1 y-intercept: Correct read-off from a point on the line and 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. 1 1(d) Value of A = candidate’s gradient and value of B = candidate’s intercept. The values must not be fractions. 1 No unit for A and unit for B correct (m, cm, mm). 1 1(e) Correct calculation of p to the number of s.f. given by the candidate. 1 1(f) Line W drawn with the same gradient but lower value of y-intercept. 1

More questions on Turning effects of forces

2 In this experiment, you will investigate the current in a coil. (a) (i) You have been provided with a bar magnet, masses and Blu-Tack. • The total mass of the mass hanger and mass should be 200 g. Use the Blu-Tack to fix the bar magnet to the mass hanger, as shown in Fig. 2.1. mass hanger total mass of 200 g Blu-Tack bar magnet Fig. 2.1 • Set up the apparatus as shown in Fig. 2.2. rod of clamp boss spring stand bench Fig. 2.2 • Pull the mass down through a short distance. Release the mass. The mass and magnet will oscillate. • Determine the period T of these oscillations. T = .......................................................... [1] (ii) Calculate the frequency f of the oscillations where 1 f = . T f = ..................................................... Hz [1] (iii) Justify the number of significant figures that you have given for your value of f. ........................................................................................................................................... ........................................................................................................................................... .......................................................................................................................................[1] (b) (i) • Take the cardboard tube with more turns of wire. • Count and record the number n of turns of wire around the tube. n = ...........................................................[1] (ii) • Connect the ammeter to the ends of the wire around the tube and place the tube below the magnet. • Adjust the height of the bottom of the magnet so that it is level with the top of the tube as shown in Fig. 2.3. crocodile clip cardboard tube A crocodile clip wire Fig. 2.3 • Pull the mass down so that it rests on the top of the tube with the magnet passing centrally through the tube. Release the mass. The mass will oscillate. • Measure and record the maximum current I shown by the ammeter. I = ..................................................... µA [1] (iii) Estimate the percentage uncertainty in your value of I. percentage uncertainty = .......................................................... [1]

Mark scheme: 2(a)(i) 1 2(a)(ii) Correct calculation of f to the number of s.f. given by the candidate. 1 2(a)(iii) Justification for s.f. in f linked to s.f. in time or period. 1 2(b)(i) Value of n. 1 2(b)(ii) Value of I. 1 2(b)(iii) Percentage uncertainty in I based on absolute uncertainty ⩾ 0.2 µA. 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 obtain percentage uncertainty. 1 2(c)(i) Second value of T. 1 Second value of T > first value of T. 1 2(c)(ii) Values of n and I. 1 Quality: second I < first I. 1 2(d)(i) Two values of k calculated correctly. 1 2(d)(ii) Valid comment consistent with calculated values of k, testing a criterion specified by the candidate. 1 Question Answer Marks 2(e)(i) A Two readings are not enough to draw a (valid) conclusion (not “not enough for accurate results”, “few readings”). B Reason for difficulty with oscillation e.g. magnet struck top of tube/magnet not passing through all turns/some turns are not near magnet/magnet oscillates outside of coil. C Difficulty in judging end/start of (complete) oscillation. D Difficulty with the current readings with reason e.g. because of positive and negative values/meter does not refresh quickly enough/current small/resistance of connecting leads high/maximum current lasts for short time. E Difficulty with the practical setup e.g. tube fell over/magnet fell off/spring moving along rod. F n is not a whole number. 1 mark for each point up to a maximum of 4. 4 2(e)(ii) A Take many readings (for different values of n or f) and plot a graph or take more values of k and compare (not “repeat readings” on its own). B Method of improving difficulty with oscillation e.g. use wider tube/use shorter tube/bunch up coils/longer magnet. C Method of improving timing e.g. put a marker with position (except at the ends)/video with timer (or replay frame by frame)/position or motion sensor placed below. D Method to reduce difficulties with current e.g. use (centre-zero) analogue meter/use c.r.o./galvanometer/use more turns of wire/smaller masses/stiffer spring/stronger magnet/sand contacts/video ammeter and replay to find maximum current. E Named method of attaching to table/holder e.g. clamp tube/tape magnet to weight/tape spring to rod/tape tube to table. F Calculate n from the length of the wire and the diameter of the tube. 1 mark for each point up to a maximum of 4. 4

More questions on Simple harmonic oscillations