Cambridge A Level Physics 9702 — 2020 Oct/Nov Paper 3 · Variant 3

1 In this experiment, you will investigate the equilibrium of a metre rule. (a) Using the calipers, determine the diameter of one of the masses. diameter = ................................................... cm [2] (b) ● Set up the apparatus as shown in Fig. 1.1, with the scale on the metre rule facing upwards. clamp boss newton meter stand 70.0 cm string loop masses 20.0 cm p A rule pivot bench Fig. 1.1 (not to scale) ● Adjust the apparatus until the pivot is 20.0 cm from end A of the rule and the string loop is 70.0 cm from end A of the rule. The pivot and string loop should remain at these positions throughout the experiment. ● Place the three masses with the edge of the bottom mass approximately 37 cm from end A of the rule. ● Adjust the stand until the newton meter and string are perpendicular to the bench. ● Adjust the boss and the clamp until the rule is parallel to the bench. ● The distance from the pivot to the edge of the mass is p, as shown in Fig. 1.1. Measure and record p. p = ......................................................... cm ● Measure and record the newton meter reading F. F = ........................................................... N [1] (c) ● Using your value of diameter from (a), calculate the radius r of a mass. r = ......................................................... cm ● Vary p in the range 5.0 cm ≤ p ≤ 45.0 cm and determine six sets of readings of p and F. For each value of p, adjust the boss and clamp until the rule is parallel to the bench. Record your values in a table. Include values of (p + r) in your table. [8] (d) (i) Plot a graph of F on the y-axis against (p + r) 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] (e) It is suggested that the quantities F and p are related by the equation W S F = (p + r) + Q Q where W = 3.00 N and Q and S are constants. Using your answers to (d)(iii), determine values for Q and S. Give appropriate units. Q = ............................................................... S = ............................................................... [3] [Total: 20] You may not need to use all of the materials provided.

Mark scheme: 1(a) Values of raw diameter either all recorded to 0.01 cm or all to 0.001 cm and final value in range 1.00–10.00 cm. 1 Evidence of repeat measurements. 1 1(b) p in range 15.0 cm ⩽ p ⩽ 19.0 cm and F in range 1.0 N ⩽ F ⩽ 5.0 N. 1 1(c) Six (or more) sets of readings of p and F (different values of non-zero p) with the correct trend and without help from the Supervisor scores 3 marks, five sets scores 2 marks, etc. 3 Range: Must include values of p ⩽ 8.0 cm and p ⩾ 42.0 cm. 1 Column headings: Each column heading must contain a quantity, a unit and a separating mark where appropriate. The presentation of quantity and unit must conform to accepted scientific convention e.g. (p + r) / cm 1 Consistency: All raw values of p must be given to the nearest 0.1 cm. 1 Consistency: All raw values of F must be given to the nearest 0.1 N. 1 Calculation: Values of (p + r) are correct. 1 Question Answer Marks 1(d)(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 points must be ⩽ half a small square. Points must be plotted to an accuracy of half a small square. 1 Quality: All points in the table (at least 5) must be plotted on the grid. Trend of points must be correct. It must be possible to draw a straight line that is within ±0.20 N (to scale) on the F axis (normally y-axis) of all plotted points. 1 1(d)(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. There must be at least five points left after the anomalous point is disregarded. Lines must not be kinked or thicker than half a small square. 1 1(d)(iii) Gradient: The hypotenuse of the triangle used must be greater than half the length of the drawn line. Method of calculation must be correct, e.g. not Δx / Δy. Gradient sign on answer line matches graph drawn. 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 correctly into y = mx + c or an equivalent expression. Read-off accurate to half a small square in both x and y directions. or Intercept read directly from the graph, with read-off at p + r = zero, accurate to half a small square. 1 Question Answer Marks 1(e) 3.00 gradient gradient W Q = = 1 3.00 -intercept -intercept gradient y S Q y × = × = 1 Units for Q and S correct (e.g. m and N m). 1

More questions on Physical quantities

2 In this experiment, you will investigate the oscillations of a square shape. (a) (i) ● Bend the wire to form a square shape so that the length L of each side is approximately 12 cm, as shown in Fig. 2.1. L wire Fig. 2.1 ● Use the wire cutters to remove any excess wire. ● Measure and record L. L = ................................................... cm [1] (ii) Estimate the percentage uncertainty in your value of L. Show your working. percentage uncertainty = ......................................................... [1] (b) (i) ● Place the cork in the clamp and attach the clamp to the stand using the boss. ● Hang the wire square from the pin as shown in Fig. 2.2. stand cork held in clamp pin wire Fig. 2.2 ● Gently displace the wire square and release it so that it oscillates as shown in Fig. 2.3. stand cork held in clamp pin wire Fig. 2.3 ● Determine the period T of the oscillations. T = ...................................................... s [3] (ii) Calculate T 2. T 2 = ..................................................... s2 [1] (iii) Justify the number of significant figures you have given for your value of T 2. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (c) ● Remove the wire square from the pin. ● Form a new square shape from the wire so that L is approximately 6 cm. ● Use the wire cutters to remove the excess wire. ● Measure and record L. L = ......................................................... cm ● Repeat (b)(i) and (b)(ii). T = ............................................................ s T 2 = ........................................................... s2 [2]

Mark scheme: 2(a)(i) Raw L to the nearest 0.1 cm and final value in the range 11.5–12.5 cm. 1 2(a)(ii) Percentage uncertainty based on an absolute uncertainty ΔL in the range 2–5 mm. If repeat readings have been taken, then the absolute 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(b)(i) All raw times measured either to the nearest 0.1 s or all to the nearest 0.01 s. 1 Evidence of measurement of nT repeated where n ⩾ 5. 1 Value of T in the range 0.5 s ⩽ T ⩽ 1.0 s. 1 2(b)(ii) Calculation of T2 correct. 1 2(b)(iii) Justification of the number of significant figures in terms of the number of s.f. in (raw) time only. 1 2(c) Second values of L and T. 1 Second value of T < first value of T. 1 2(d)(i) Two values of k calculated correctly. The final k values must not be fractions. 1 2(d)(ii) Valid comment consistent with the calculated values of k, testing against a criterion stated by the candidate. 1 2(e) Correct calculation of g using candidate’s second k and in range 2.0 m s–2 ⩽ g ⩽ 20.0 m s–2. 1 Question Answer Marks 2(f)(i) A Two readings are not enough to draw a (valid) conclusion (not “not enough for accurate results”, “few readings”). B Difficulty in measuring time or T with a reason, e.g. judging when to start or stop the stop-watch, judging start/end/complete oscillation. C Difficulty in measuring L with a reason, e.g. wire is not straight/is kinked/has rounded corners. D Corners are not at right angles or square not complete/joined or shape changes when suspended/during oscillation. E Oscillations are not in one plane or square catches on drawing pin. 1 mark for each point up to a maximum of 4. 4 2(f)(ii) A Take more readings and plot a graph or take more readings and compare k values (not “repeat readings” on its own). B Method of improving time or T, e.g. fiducial marker at centre/video (or record or film) and timer (or frame-by- frame)/place a grid behind the apparatus. C Method of improving L, e.g. use thicker/stiffer wire or use a former/shaping block. D Method of improving the setting of 90° corners, e.g. use a set square or protractor with appropriate reason or method of fixing ends, e.g. use adhesive putty/tape with appropriate reason. E Method of improving oscillation, e.g. longer pin/use of guide with detail/groove in pin/use a nail/use a hook. 1 mark for each point up to a maximum of 4. 4

More questions on Physical quantities