SAJC 2024 J2 H2 Physics Prelim P4 Soln

1 Mark Scheme for 2024 SAJC Prelims P4 Q1 ( A-lev Pract in 2023) No Marking Point Score (a) € Recorded R as labelled, ie 68 Ω (as per question) € Recorded I as shown on display, ie to nearest 0.1 mA € Accuracy: range of I : 110.0– 130.0 mA € Recorded repeat measurements of y to nearest mm ( ie to 1 mm, 0.1 cm or 0.001 m) € Recorded average value of y to same dp as its raw readings ( ie to nearest mm) /1 (b) Tabulation € At least 5 sets of readings of R & repeated y. /1 Column Headings inTable € Each column heading must have a quantity and a unit: eg R /Ω, y/cm, R/y. /1 Precision of Recording For Raw Data: € Recorded all R to nearest Ω (as labelled) € Recorded all y to nearest mm € Recorded all I to nearest 0.1 mA (if recorded) For Calculated Data: ( eg for R/y, IR, 1/R, 1/y)  Correct no. of sf (which takes into account consistency within a given column) /1 (c) Graph: Scale, Size & Axes € Sensible scales, ie no awkward scales (eg 3 units into 10 small squares) € Plotted pts occupy at least ½ the graph grid in both x & y directions € Axes labelled with the quantity & unit € Successive scale markings: not more than 20 small squares apart. /1 Plotting of Points € ALL observations in table must be plotted € Accurate to within half a small square. € Thickness of plots (ie the crosses, ‘x’)  half a small square /1

2 Best fit line & Anomaly € Straight line drawn with approx. equal number of points on either side of line (anomalous point not considered). € Line must not be kinked/disjointed or thicker than half a small square € Anomalous plot clearly indicated (eg by a circle or labelled “anomaly”.) € Maximum number of anomalous plot allowed: 1 /1 Correct Trend: ( Not awarded for Inappropriate graph) Appropriate graph using data where as R increases, y decreases. /1 Determination of Gradient ( Not awarded for Inappropriate graph) € Gradient coordinates clearly indicated on graph and in working (accurately recorded) € Precision of gradient coordinates: either to 3 sf or to ½ a small square € Hypotenuse of triangle > half length of line drawn € No obscurity of the 2 points used for gradient calculation. {Hence triangle must not be drawn too near a data plot.} € Precision of gradient: either to 3 sf, or, same number of sf as the coordinate with the least number of sf, or 1 more. € Value of F: calculated correctly to 3 sf. ( Accept 4 sf ) /1 Units of the unknown constants  F: A Ω, or V ( Accept mA )  Q: Ω m-1 ( Accept  cm-1) /1 Determination of y-intercept ( Not awarded for Inappropriate graph) € y-intercept calculated using a point on the line {not from the table} & value of gradient. € Value of Q: a POSITIVE value, 3 s.f. ( Accept 4 sf ) Or, € Reading off the y-intercept if x-axis starts from zero ( ie no false origin) € Value of Q: a POSITIVE value, precision to ½ small square /1 Linearisation of Equation