2019 AHS Physics Prelim Paper 3 Mark Scheme

Marking Scheme for 2019 Prelim Physics Paper 3 1(b) Time measurement for at least 5 oscillations AND working to calculate T [1] T = 2.24 s (accept either 1 dp OR 2 dp) [1] (cii) t = 22.41 s (accept either dp OR 2 dp) [1] [t > 10 s] [-1m for any inaccuracy in precision and unit in (b) & (cii)] (ciii) Energy lost to the surrounding due to air resistance / friction. [1] (d) Constant variable(s) – H / angle of swing / amplitude kept 10 to 12 cm Independent variable – mass m of pendulum bob. [1] 1. Set the apparatus as shown in the diagram (Fig. 1.1) 2. Suspend a pendulum bob of 100 g, move the bob to align with the 12 cm mark on the card as shown in Fig. 1.2 3. Release the pendulum bob. Measure and record the time t for the amplitude of the pendulum to decrease from 12 cm to 10 cm. [1] 4. Repeat step 3. Take average of the two readings for t. [1] 5. Repeat step 2 to 4 for 5 more different sets of readings by varying m. [1] 6. Plot a graph of t against m. [1] 7. Shows a sketch of the graph with best-fit line that passes through origin] [1] 2 (ai) lo = 2.0 cm to 3.0 cm [1] (aii) ls = 7.5 to 8.5 cm [1] eo = 4.5 cm to 6.5 cm [correct calculation for eo] [1] [-1m for any inaccuracy in precision and unit in both ai and aii] (b) k = 0.26 Ncm-1 [correct calculation of k] [1] [-1m for any inaccuracy in unit] (ci) & (cii) correct calculation for e1 and e2 [1] each (d) F1 = 0.90 N [1] F2 = 2.0 N [1] [correct calculation for both F with correct significant figures] [accept ecf of e in calculation of F] (e) There is friction [1] between the pipe and the string [1].

3 (a) I = 0.20 to 0.35 A [1] [correct precision with unit] (b) V = 0.10 to 0.20 V [1] [correct precision with unit] (c) x / cm V / V 10.0 0.10 15.0 0.15 25.0 0.30 35.0 0.40 45.0 0.60 60.0 1.75 65.0 1.80 75.0 2.00 85.0 2.10 90.0 2.20 Include all 9 sets of data (x = 15 to 90 cm) [1] Include value of x and V from 3(b) [1] Correct headings and units [1] Correct precision for both x and V [1] (d) Axes labelled with units and correct orientation (allow ecf from wrong unit in table but not no unit) [1] Suitable scale, not based on 3, 6, 7 etc. with combined plotted data of the two lines occupying more than or greater than half the page in both directions. x-axis atart with 0 and end with 100 cm [1] All points plotted correctly (points must be less than or equal to ½ small square from the correct position. [1] Best-fit line with labelling of graphs A and B [1] (e) & (f) GA = 0.014 Vcm-1 GB = 0.015 Vcm-1 [Correct calculation of gradient GA and GB] [1] [Both the triangles uses more than half the individually drawn line] [1] V A = 0 V VB = 0.80 V [VA and VB read or determined correctly from graph] [1] [G calculated in 2 or 3 sf & V read from one half of one of the smallest squares on the grid with correct units] [1] (g) Agreed. [1] The results obtained for both GA and GB are approximately the same. OR Disagreed. [1] The results obtained for both GA and GB have great difference.[1] [answer will depend on the data of GA and GB from 3(e) & (f).

(hi) L = 57 cm Correct calculation of L [1] with unit and correct number of sf based on the raw data [1] (hii) 1. The wire on the metre rule is not straight. This affects the accuracy of the readings of x. [1] 2. As the switch is open only after the 10 readings are taken, there is overheating of the wire. This will affect the accuracy of the readings of V. [1] (Answer should state the source of error and specify which reading is affected as a result of the error.)