Cambridge A Level Physics 9702 — 2011 May/June Paper 3 · Variant 3

1 In this experiment you will investigate how the motion of a paper strip depends on its width. Use (a) (i) Measure and record the width x of the thin paper strip, as shown in Fig. 1.1. x Fig. 1.1 x = .......................................... cm [1] (ii) Connect the clips to the strip, as shown in Fig. 1.2. 26 cm clip clip wooden rod Fig. 1.2 (b) (i) Set up the apparatus with the top clip supported on the nail, as shown in Fig. 1.3. For Examiner’s Use nail nail clip clip paper strip paper strip clip clip wooden rod wooden rod bench front view side view Fig. 1.3 (ii) Twist the wooden rod through an angle of approximately 45° in a horizontal plane, For as shown in Fig. 1.4. Examiner’s Use wooden rod one complete swing approximately 45° Fig. 1.4 Release the rod and watch its movement. The wooden rod completes one swing by twisting one way and then back the other way, as shown in Fig. 1.4. The time taken for each complete swing is T. By timing several of these complete swings, determine an accurate value for T. T = ................................................ [2] (c) By cutting new strips from the graph paper, repeat (a) and (b) until you have six sets of For values of x and T. Values of x should be in the range 1 cm ≤ x ≤ 6 cm. Examiner’s Use 1 Include values of in your table of results. x [9] 1 (d) (i) Plot a graph of T on the y-axis against on the x-axis. [3] x (ii) Draw the straight line of best fit. [1] (iii) Determine the gradient and y-intercept of this line. gradient = ..................................................... y-intercept = ..................................................... [2] For Examiner’s Use (e) It is suggested that the relationship between T and x is For a Examiner’s T = + b Use x where a and b are constants. Using your answers from (d)(iii), determine the values of a and b. Give appropriate units. a = ..................................................... b = ..................................................... [1] (f) State one problem with determining an experimental value of T for x = 15 cm. .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .......................................................................................................................................... .................................................................................................................................... [1] You may not need to use all of the materials provided. For Examiner’s

Mark scheme: 1 (a) (i) Value of x in the range 1 cm – 3 cm. [1] (b) (ii) Value of T in range 1.8 s T 4.5 s with consistent unit. [1] If outside this range allow SV ± 40% (write in SV if used). Evidence of repeat times. [1] (c) Six sets of readings of x and T scores 4 marks, five sets scores 3 marks etc. [4] Incorrect trend then –1. Help from supervisor –1. Range of x : To include 1 cm and 6 cm. [1] Column headings: [1] Each column heading must contain a quantity and a unit. There must be some distinguishing mark between the quantity and the unit e.g. T / s. Ignore POT errors. Ignore units in body of table. Consistency of presentation of raw readings: [1] All values of x must be given to the nearest mm. Significant figures: Significant figures for every row of 1/x same as, or one more than, raw x. [1] Calculation: 1/x calculated correctly. [1] (d) (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 on the grid occupy at least half the graph grid in both x and y directions. Indicate false origin with FOX. Scales must be labelled with the quantity which is being plotted. Ignore units. Scale markings should not be more than three large squares apart. Plotting of points: [1] All observations in table must be plotted. Write a ringed total of plotted points ignoring any point off the grid. Check points plotted correctly. Tick if correct. Re-plot if incorrect. Work to an accuracy of half a small square. Do not accept ‘blobs’ (points with diameter greater than half a small square). Quality: [1] All points in the table must be plotted (at least five) for this mark to be scored. Judge by scatter of all points about straight line. All points must be within 0.05 cm–1 of 1/x from a straight line. (ii) Line of best fit: [1] Judge by the balance of all the points (at least five) about candidate’s line. There must be an even distribution of points either side of the line along the whole length. If mark is not awarded indicate rotation or direction of best fit line. Lines must not be kinked. GCE A LEVEL – May/June 2011 9702 33 (iii) Gradient: [1] The hypotenuse of the triangle must be at least half the length of the drawn line. Read- offs must be accurate to half a small square. Check for ∆y/∆x (i.e. do not allow ∆x/∆y). If incorrect, write in the correct value(s). y-intercept: [1] Either: check correct read off from a point on the line and substitute into y = mx + c. Read off must be accurate to half a small square. Allow ecf of gradient value. Or: check read-off of intercept directly from graph. (e) a is the value of candidate’s gradient with consistent unit (s (c)m or (c)m s). [1] b is the value of candidate’s y-intercept with consistent unit (s). (f) Either: Strip too wide for clips. [1] Or: time too small (to measure). [Total: 20]

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2 In this experiment you will investigate the deflection of a metre rule when a mass is suspended Use from its centre. (a) (i) Set up the apparatus as shown in Fig. 2.1 with a distance l between the supports of approximately 95 cm. l support metre rule h0 block bench Fig. 2.1 (ii) Measure and record l. l = ................................................ [1] (iii) Midway between the supports, measure and record the height h0 of the bottom of the rule above the bench. h0 = ................................................ [1] (b) (i) Use the small loop of string to suspend the mass from the rule, midway between the supports. (ii) Midway between the supports, measure and record the new height h of the bottom of the rule above the bench. h = ................................................ [1] (iii) Calculate the deflection d of the beam where d = h0 – h. For Examiner’s Use d = ................................................ [1] (c) Estimate the percentage uncertainty in your value of d. percentage uncertainty = ................................................ [1] (d) Change l to approximately 60 cm. Repeat (a)(ii), (a)(iii) and (b). l = ..................................................... h0 = ..................................................... h = ..................................................... d = ..................................................... [4] (e) It is suggested that the quantities d and l are related by the equation For Examiner’s d = k l 3 Use where k is a constant. (i) Using your data, calculate two values of k. first value of k = ...................................................... second value of k = ..................................................... [1] (ii) Explain whether your results support the suggested relationship. .................................................................................................................................. .................................................................................................................................. .................................................................................................................................. ............................................................................................................................ [1] (iii) Justify the number of significant figures that you have given for your values of k. .................................................................................................................................. .................................................................................................................................. ............................................................................................................................ [1]

Mark scheme: 2 (a) (ii) Measurement of raw l to nearest mm in the range 90 cm – 100 cm. [1] (iii) Value of h0 with unit. [1] (b) (ii) Value of h < h0. [1] (iii) Check correct calculation of d. [1] (c) Absolute uncertainty in d in the range 1 mm – 2 mm or half the range of repeated readings, unless zero. Correct method of calculation to get percentage uncertainty. [1] (d) Second value of l in range 55 cm l 65 cm. [1] Second value of h0. [1] Second value of h < h0. [1] Quality : second value of │d│ < first value of │d│. [1] (e) (i) Correct calculation of two values of k. [1] (ii) Sensible comment relating to the calculated values of k, testing against a specified criterion. [1] (iii) Justification of sf in k linked to l and d. [1] GCE A LEVEL – May/June 2011 9702 33 (f) (i) Limitations 4 max (ii) Improvements 4 max Do not credit Ap Two readings (of d and l) not enough/ As Take more readings and plot a Take more only two readings/ too few readings graph/ more values of k (and readings and compare). calculate average k / only one reading Bp Difficult to measure h with reason/ Bs Detailed use of set square or Mass gets in parallax error in h pointer to improve parallax/ the way. method for easier access/ method of reducing parallax Cp d is small Cs1 Larger mass Cs2 Method to measure d directly e.g. using a travelling microscope or position sensor Dp Rule may not be vertical (when Ds Detailed use of set square (table measuring h) level) Xp Specific problem candidate Xs e.g. glue support to block Ignore encountered e.g. ruler slips on reference to support/supports slip on block computers, using assistance, draughts [Total: 20]

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