2023 HCI H2 PH Prelim P4 MS

1 © Hwa Chong Institution 2023 2023 Prelim Practical Exam Mark Scheme and Examiners Comments Question 1 [10 marks] Part Marking Point Mark (a) Value of b in the range 11.8 to 12.2 cm Value of c in the range 15.8 to 16.2 cm [1] (b) Value of y in measured to nearest 1 mm Value of y in the range 4.6 to 5.0 cm [1] [1] (c)(i) Value of c in the range 9.8 to 10.2 cm [1] (c)(ii) Value of y in the range 4.9 to 5.3 cm [1] (d)(i) Value of y is calculated correctly with units and expressed to 2 or 3 s.f. [1] (d)(ii) Correct identification of graph to be plotted. (Gradient and y-intercept expressions should not include y and/or c) [1] (d)(iii) Correct expression stated for the gradient. Correct expression stated for the y-intercept. (Gradient and y-intercept expressions should not include y and/or c) [1] [1] (e) Reasonable explanation why value of y is equal to 6 cm. (E.g. when y is zero, the card becomes a square or rectangle, hence the centre of gravity is at the midpoint/middle/centre of the card. [1]

2 © Hwa Chong Institution 2023 Question 2 [11 marks] Part Marking Point Mark (a) Value of I2 in the range 50.0 to 80.0 mA I2 > I1 [1] (b) 6 sets of raw data + appropriate Ry range (accept 0 or 1 d.p precision) + correct trend of I1 / I2 ratio Column headings: 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 Correct precision for raw data and s.f for calculated data. Correct calculation. [1] [1] [1] (c) Linearization: Graph of I1/I2 vs RY graph plotted. If wrong linearization, penalize Rx. 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. Scale markings should be no more than three large squares apart Plotting of points: All observations in the table must be plotted on the grid. Points must be plotted to an accuracy of half a small square. Line of best fit or BFL: 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. Gradient: 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. RX calculated correctly with units from gradient (e.g. = 1/2RX ), appropriate range from 10 to 40 Ω. Penalise Rx if 1 s.f. [0] [1] [1] [1] [1] [1] (d) As RY = RX, RX can be determined from the graph by identifying the RY value when I1 / I2 =