Cambridge A Level Physics 9702 — 2021 Oct/Nov Paper 3 · Variant 1

1 In this experiment, you will investigate oscillations. (a) ● Slide the loop of a spring onto a wooden rod. Fix the loop of the spring in the middle of the wooden rod with a clip, as shown in Fig. 1.1. wooden rod spring clip loop Fig. 1.1 ● Use half of the adhesive putty to fix four 10 g masses to the wooden rod as shown in Fig. 1.2. two 10 g masses two 10 g masses § 22 cm adhesive putty Fig. 1.2 ● Adjust the positions of the masses until the distance between the masses is approximately 22 cm. The masses should each be approximately the same distance from the clip, as shown in Fig. 1.2. ● Clamp the loop at the top of the spring between two small wooden blocks. ● Arrange the apparatus as shown in Fig. 1.3. stand clamp wooden blocks boss loop bench x Fig. 1.3 ● Adjust the position of the clip until the rod balances approximately parallel to the bench. ● The distance between the masses on the wooden rod is x, as shown in Fig. 1.3. Measure and record x. x = ......................................................... [1] (b) ● Using the other wooden rod, set up a second set of apparatus as shown in Fig. 1.3. ● The distance between the masses on this wooden rod is p. Adjust the position of the masses until the value of p is approximately 18 cm. ● Measure and record p. p = ......................................................... [1] (c) ● Move the apparatus until the two rods are close to each other and in line as shown in Fig. 1.4. X P x p Fig. 1.4 ● Gently press the rods down at end X and end P. ● Release the ends at the same time. The ends will oscillate as shown in Fig. 1.5. X P Fig. 1.5 ● Watch the oscillations. X and P move in and out of phase. ● Look at P. Count the number n of oscillations made by P from release until both ends are back in phase. n = ......................................................... [1] (d) Change p in the range 14.0 cm  p  20.5 cm and repeat (c) until you have six sets of values of p and n. Keep distance x constant. 1 1 Record your results in a table. Include values of and in your table. p n 1 Record the values of to three significant figures. n [9] 1 1(e) (i) Plot a graph of on the y-axis against on the x-axis. [3] n p (ii) Draw the straight line of best fit. [1] (iii) Determine the gradient and y-intercept of this line. gradient = ............................................................... y-intercept = ............................................................... [2] (f) It is suggested that the quantities n and p are related by the equation 1 A = + B n p where A and B are constants. Using your answers in (e)(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(a) Value of x with unit and in the range 21.0–23.0 cm. 1 1(b) Value(s) of p to nearest mm and final value with unit and in the range 17.0–19.0 cm. 1 1(c) Value of n with evidence of repeats. 1 1(d) Six sets of readings of p (different values) and n with correct trend and without help from Supervisor scores 4 marks, five sets scores 3 marks etc. 4 Range: pmin ⩽ 15.0 cm and pmax ⩾ 19.0 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. p / cm, (1 / p) / (1 / m) or p–1 / mm–1. There must be no unit for n or 1 / n. 1 Consistency: All values of p must be given to the nearest mm. 1 Significant figures: All values of 1 / p must be given to the same number of s.f. as, or one greater than, the number of s.f. of the p values as recorded in the table. 1 Calculation: Values of 1 / p are correct. 1 Question Answer Marks 1(e)(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 the x and y directions. Axes 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 in both x and y directions. 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 ± 0.002 cm–1 on the 1 / p axis of all plotted points. 1 1(e)(ii) Line of best fit: Judge by the 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. There must be at least five points left after the anomalous point is disregarded. Line must not be kinked or thicker than half a small square. 1 1(e)(iii) Gradient: The hypotenuse of the triangle used must be greater than 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. Method of calculation must be correct, e.g. Δy / Δx. Gradient sign on answer line matches graph drawn. 1 y-intercept: Correct read-off from a point on the line and substituted 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 1 / p = 0, accurate to half a small square. 1 Question Answer Marks 1(f) Value of A = candidate’s gradient and value of B = candidate’s intercept. Values must not be written as fractions. 1 Unit for A correct e.g. cm, m or mm and no unit given for B. 1

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2 In this experiment, you will investigate the flow of oil. (a) You have been provided with two straws of the same diameter. (i) Measure and record the length l of the shorter straw. l = ......................................................... [1] (ii) The diameter D of the straw is shown in Fig. 2.1. D Fig. 2.1 Measure and record D. D = ......................................................... [1] (iii) Calculate the volume V of the straw using πD2l V = . 4 V = ......................................................... [1] (iv) Justify the number of significant figures that you have given for your value of V. ........................................................................................................................................... ........................................................................................................................................... ..................................................................................................................................... [1] (b) Draw a circle of radius 2.0 cm on the blank sheet of paper. (i) ● Place a Petri dish on top of the circle on the paper. ● Use small pieces of adhesive putty at the edge of the Petri dish to secure it to the paper. ● Place a small piece of adhesive putty at the centre of the Petri dish. ● Gently press the straw into the adhesive putty so that the bottom of the straw is sealed by the putty. ● Arrange the apparatus as shown in Fig. 2.2 and Fig. 2.3 with the straw above the centre of the circle drawn on the paper. TOP VIEW paper adhesive putty circle on paper straw Petri dish Fig. 2.2 SIDE VIEW straw Petri dish adhesive putty adhesive putty bench paper Fig. 2.3 ● You have been provided with plastic gloves to wear when handling the oil. Use the dropper to fill the straw with oil. ● When the straw is lifted from the putty, the oil spreads out. The time taken for the first part of the oil to reach the circle is t. Gently lift the straw away from the putty. ● Measure and record t. t = ......................................................... [2] (ii) Estimate the percentage uncertainty in your value of t. Show your working. percentage uncertainty = ......................................................... [1] (c) Repeat (a)(i), (a)(iii) and (b)(i) using the longer straw. l = ............................................................... V = ............................................................... t = ............................................................... [3]

Mark scheme: 2(a)(i) 1 2(a)(ii) Value(s) of raw D all to nearest 0.01 cm or all to nearest 0.001 cm and final value of D with unit and less than 1.0 cm. 1 2(a)(iii) Correct calculation of V. 1 2(a)(iv) Justification for significant figures in V linked to number of s.f. in D and l. 1 2(b)(i) Value of time t > 1.0 s with unit. 1 Evidence of repeated values of t. 1 2(b)(ii) Percentage uncertainty based on an absolute uncertainty in t in the range 0.2–5 s. 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 find percentage uncertainty. 1 2(c) Second value of l. 1 Second value of t. 1 Second value of t is less than first value of t. 1 2(d)(i) Two values of k calculated correctly. The final k values must not be written as fractions. 1 2(d)(ii) Valid comment consistent with the calculated values of k, testing against a criterion stated 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 Difficulty in measuring time t with a reason (at the start or at the finish) e.g. lifting straw and starting stopwatch simultaneously/judging or predicting when to stop timing. C Difficulty linked to oil with detail e.g. difficult to see as colourless/clear/transparent or some oil left in straw drips out later/oil leaks from straw/paper straw absorbs oil. D Difficulty linked to raising or positioning the straw e.g. not always in centre/hand moves when lifted/straw tilted/putty obscures the centre. E Problem with volume V with reason e.g. D is the external diameter/no account of thickness of straw/squashing straw/putty goes up straw/oil left in straw. 1 mark for each point up to a maximum of 4. 4 2(e)(ii) A Take more readings and plot a graph or take more readings and compare k values (not “repeat readings” on its own). B Improved method to measure t e.g. video/film/ record with timer/view frame by frame. C Improved method to see oil e.g. add dye or improved method to contain the oil e.g. flap/cap/plastic straw. D Improved method to release or positioning of straw e.g. clamp a laser with beam above the centre point/clamp a guide at the centre/draw a cross on the paper. E Valid method to measure internal straw diameter e.g. travelling microscope or method to measure thickness directly e.g. cut open and use micrometer to measure wall thickness. 1 mark for each point up to a maximum of 4. 4

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