Physics 9702/31 May/June 2020: question paper and mark scheme

Mark scheme

1(a) Value of V with unit in the range 0.400–0.500 V. 1 1(b) Six sets of readings of R and V (different values) showing the correct trend and without help from the Supervisor scores 4 4 marks, five sets scores 3 marks etc. Range: Values of R must include 12 Ω and 18 Ω and 39 Ω. 1 Column headings: 1 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. 1 / V / V–1 and R / Ω. Consistency: 1 All values of V must be given to the nearest 0.001 V (or 1 mV). Significant figures: 1 All values of 1 / V must be given to the same number of s.f. as, or one more than, the number of s.f. in V. Calculation: Values of 1 / V are correct. 1 1(c)(i) Axes: 1 Sensible scales must be used, no awkward scales (e.g. 3:10). 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. Plotting of points: 1 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. Quality: 1 All points in the table (at least 5) must be plotted on the grid. Trend of points on graph must be correct. It must be possible to draw a straight line that is within 0.05 V–1 on the 1 / V axis of all plotted points. 1(c)(ii) Line of best fit: 1 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. If there are 6 or more points, allow one anomalous point only if clearly indicated by the candidate. Line must not be kinked or thicker than half a small square. 1(c)(iii) Gradient: 1 The hypotenuse of the triangle used must be greater than half the length of the drawn line. The method of calculation must be correct. Do not allow Δx / Δy. Both read-offs must be accurate to half a small square in both the x and y directions. y-intercept: 1 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(d) Value of A = candidate’s gradient and value of B = candidate’s intercept. 1 The values must not be fractions. Unit for A correct (e.g. Ω V–1 or Ω mV–1) and unit for B correct (e.g. V–1 or mV–1). 1 1(e)(i) E calculated correctly using E = 2 / y-intercept or E = 2 / B. 1 1(e)(ii) X correctly determined e.g. calculation of 3 / E, read-off of the corresponding value of 1 / R from the graph, then calculation 1 of X or using X = A / (3 / E – B) or using X = EA.

Mark scheme

2(a)(i) Value of L to the nearest mm in the range 98.5–99.5 cm with unit. 1 2(a)(ii) Correct calculation of L / 3. 1 2(b)(i) Measurement of θ to the nearest degree. 1 Value of θ in the range 0°─20°. 1 2(b)(ii) Percentage uncertainty in θ based on absolute uncertainty in the range 2°–5°. 1 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. 2(b)(iii) Correct calculation of sin θ. 1 2(b)(iv) Justification for s.f. in sin θ linked to s.f. in θ. 1 2(c) Second value of θ. 1 Quality: Second value of θ > first value of θ. 1 2(d)(i) Two values of C calculated correctly. 1 2(d)(ii) Valid comment consistent with calculated values of C, testing against a criterion stated by the candidate. 1 2(e) Value of k correctly calculated and in the range 10–20 N m–1 and with consistent unit. 1 2(f)(i) A Two readings are not enough to draw a (valid) conclusion (not “not enough for accurate results”, “few readings”). 4 B Difficult to measure θ with reason e.g. holding protractor and hand moves. C Rule slips on clamp. D Difficult to know when rule is horizontal. E Difficulty linked to setting L / n with a reason e.g. stands move suddenly/friction between bench and stands. F Difficult to hold one end of the rule and adjust the other end at the same time. 1 mark for each point up to a maximum of 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). 4 B Mount protractor on block/use another ruler and use trigonometry to determine angle. C Use adhesive putty/tape on rod. D Use spirit level/another rule to ensure horizontal. E Method to ensure smooth movement of stands e.g. mount stands on wheels/rollers. F Use a third stand and clamp to hold the free end of the rule. 1 mark for each point up to a maximum of 4.