EJC 2023 J1 H2 Promo P4 MS

No Marking Instructions Mark 1(a)(i) • Total mass of at least 5 paper clips measured. Average mass of each paper clip to be computed from total mass. 1 Examiner’s Comments Given that 1 paper clip is very light, students should take the measurement of a larger number of paper clips and finding the average. Measuring a larger quantity would reduce the percentage uncertainty of the measured value. • Value of each paper clip < 1.20 g • Value of each paper clip stated to the correct precision and recorded with an appropriate unit. 1 Examiner’s Comments Final value should be given to the same s.f. as the measurement done. 1(a)(ii) • Average of at least 2 readings. • Must be whole number if the average of 2 consecutive numbers given. 1 Examiner’s Comments When asked for any quantity, always repeat the experiment to find average – no difference in this case! 1(b)(i) • Average of at least 2 measurements. • 125° ≤ θ ≤ 155°. • θ recorded to the correct precision (nearest degree) with unit (degree o) 1 Examiner’s Comments Angles must be measured to nearest whole degree! 1(b)(ii) • 2° ≤ ∆θ ≤ 8°. • Correct calculation. • % uncertainty to 2 s.f. • If repeated readings have been taken, then absolute uncertainty can be computed as follows with full working clearly shown: ( )max min 2/θθ θ∆= − . This method is not valid if the computed value ∆θ = 0, or ∆θ ≤ precision of instrument. 1 Examiner’s Comments Common errors: • θθ θ∆= − max min : NOT correct! • ∆θ should be a whole number 1(c)(i) • Value of M calculated correctly with appropriate s.f. (2 or 3) and units. Examiner’s Comments Question well done generally. A common mistake is to omit the unit for mass, g. 1 1(c)(ii) • Clear explanation or working showing how the maximum value of M can be obtained. • V alues of (a)(ii) and (b)(ii) to be explicitly used • Maximum value of M correctly calculated with appropriate s.f. (2 or 3) and units. Examiner’s Comments Question well done generally. Students need to realise that max M requires cos θ to be a minimum. Correspondingly this would require θ to be a maximum. Also, the maximum number of paper clips required found in (a)(ii) should be taken into consideration when finding max M. 1

1(c)(iii) • Average of at least 2 measurements. • Value of θ in (c)(iii) less than the value of θ in (b)(i). • θ is recorded to the correct precision (nearest degree) with unit (degree o) Examiner’s Comments Common errors: • only one reading taken (MUST take repeated reading!), • expressing the angle measured to 0.1 degree (MUST give to whole number!) • omtting the unit for the angle measured (MUST give units!) 1 1(d)(i) • k1 & k2 calculated correctly and given to appropriate s.f. • k1 & k2 given correct units. Examiner’s Comments Common errors: • omitting the unit for k • taking m = 50 g for both θ measured. 1 1 1(d)(ii) • Percentage difference in the two k values calculated correctly and given to 2 s.f. • Correct conclusion given with reasoning. Examiner’s Comments Minority of scripts did not apply the formula for percentage difference correctly or failed to compare the percentage difference in k with percentage uncertainty in θ as required. 1 1 1(e)(i) Accepted sources of error Usually expect problem + quantity for sources of error. But in this case, the quantity is given, so stating θ becomes a good practice rather than a requirement. i) Difficult to measure θ accurately, using a protractor held in one’s hand, because of unsteady hands ii) Friction present in the ball bearings of the pulley causes the setup to be stable over a range of θ. iii) The hook of the hanger makes it impossible to place the protractor close to the setup. This affects the measurement of θ. iv) Difficult to gauge where the vertical axis is. This makes it difficult to ensure that θ is symmetrical about the vertical axis. Examiner’s Comments 1. Many students thought that the height of the 2 ends of the strings must be the same. This is not the case. 2. Answers like difficult to measure angle θ will not be accepted if the difficulty is not elaborated correctly. 3. Some students also wrote answers like wind/parallax error and no mark w as awarded as well. Max 1 1(e)(ii) Corresponding improvement i) Clamp the protractor with a retort stand, so that it is stable. ii) Lubricate the axle of the pulley. iii) Tie the hanger to a string loop, and hang the loop through the string in Fig 1.2 iv) Use a plumb line to indicate the vertical axis as a fiducial marker. or Measure the horizontal distance to ensure the mass is hung at the mid -point. (This is not entirely true because the height of the 2 ends of the strings are not the same.) BOD – You may have kept the height the same. Do not accept: 1. Use trigo to calculate angle θ because most assumptions are wrong. Using metre rule to measure the length will incur error as well. 2. Many students used video/photograph to ensure the angle is symmetrical. This is also not accepted because the camera is not aligned and will incur more error. Max 1

[Total: 14 Marks] No Marking Instructions Mark 2(a)(iii) • Average of at least 2 measurements. • 1 30° ≤ θ ≤ 150°. • θ recorded to the correct precision (nearest degree) with unit (degree o) Examiner’s Comments Common errors: • Units and evidence of repeated readings were often missed out. • Precision was wrong (Correct: 1°, Wrong: 0.1°) 1 2(b)(iii) • Number of oscillations stated. BOD given if not defined but can be inferred from calculation • Evidence of repeated measurements of t. BOD given if main table has repeated measurement of the same reading. • t recorded with the correct precision (2 d.p.) and unit. • t ≥ 15 s • T calculated correctly and given to the correct s.f. (4 SF) with an appropriate unit. Examiner’s Comments Common errors: • wrong units (s-1) • t < 15 s • T not in 4 sf. 1 2(c) • 6 or more sets of data without assistance/ intervention. 1 • Range of θ > 80° 1 • Correct trend: as θ decreases, T decreases 1 • Each column heading must contain a quantity with an appropriate unit. (minimally must have θ, t , 4 1 T and cos θ) Examiner’s Comments Most students could not write correctly the column heading ( )cos /θ ° . 1 All raw measurements are recorded to the correct precision • t to the nearest 0.01 s • θ to the nearest degree 1 • All processed data are correctly calculated and given to the correct s.f. 1 Number of oscillations shown AND evidence of repeated measurements of t for each value of θ AND t ≥ 15 s 1 [minus 1] Split table Examiner’s Comments Quite a number of students did not draw in the table lines. Many recorded their readings in pencil instead of using a pen. Note that doing all these reduce the readability of the table, and candidates might be penalised in the A-level Exam. Students who did not do well for this section obviously have not studied the Practical Guide notes, or the many past Sample reports.

2(d)(i) Graph Axes • 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 and units which are being plotted. • Scale markings should be no more than 4 cm apart. Examiner’s Comments Please approach tutor for clarification if you do not know what is considered a small graph (see point 2 above). 1 Graph Plotting of points • All observations must be plotted on the grid. • Plots must be accurate to within half a small square in both x and y directions. Examiner’s Comments • Learn how to calculate how many squares a certain point is. (See below) • Do NOT put a cross for gradient coordinates or y-intercept.