NJC 2024 H2 Physics Prelim P4 Ans

NJC Preliminary Examination 2024 H2 Physics Paper 4 Question Marking points Marks 1(a) Value of 𝑅𝐴 and 𝑅𝐵 recorded to nearest 0.1 Ω m-1. 1 1(b)(i) Values recorded to nearest 0.1 cm with correct unit (cm). 1 x > y. 1 1(c) Six sets of readings of x and y including the data from (a) without assistance. Correct trend of increasing x and y 1 Range: Smallest 20 cm ≤ x ≤ 30 cm and largest x ≥ 80 cm. 1 Each column heading (x, y, and ) contains a quantity and a unit. 1 All calculated values and must be given to the same number of significant figures as the raw values. 1 1(d) Axes: ● Sensible scales must be used, no awkward scales (e.g. 3:10 or fractions). ● Scales must be chosen so that the plotted points occupy at least half the graph grid in both x and y directions. ● Axes must be labelled with the quantity which is being plotted. ● Scale markings should be no more than two large squares apart. 1 Plotting of points: ● 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 in both the x and y directions. 1 Line of best fit: ● Judge by balance of all points on the grid about the candidate’s line (at least 6 points). There must be an even distribution of points either side of the line along the full length. ● Allow one anomalous point only if clearly indicated. There must be at least five points left after the anomalous point is disregarded. ● Lines must not be kinked or thicker than half a small square. 1 Gradient: ● The hypotenuse of the triangle used must be greater than half the length of the drawn line. ● Method of calculation must be correct, i.e. ∆y / ∆x. ● Gradient sign on answer line matches graph drawn. ● Both read-offs must be accurate to half a small square in both the x and y directions. 1 y-intercept: Check 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 at x = 0, accurate to half a small square. 1 Value of a = gradient with no unit. 1 Value of b = y-intercept with correct unit (cm–1 or m–1). 1 1(e) Correct calculation of Internal resistance r and r must be positive 1

2 Question Marking points Marks 2(b)(ii) Value of θ recorded to the nearest degree with correct unit. 1 L ≥ L0, expressed to 1 decimal place 1 2(c) Value of e calculated from L – L0. 1 Correct calculation of k. 1 2(d) m is varied to obtain angle θ, adjust the apparatus to keep the length of spring or extension of the spring fixed (and PQ horizontal) or m is varied to obtain extension of spring e, adjust the apparatus to keep θ fixed. 1 Plot a graph of cos 𝜃 against m or Plot a graph of e against m 1 State how k is calculated e.g. k = g / (cos 𝜃 × gradient) or k = g / (e × gradient) 1 Questio n Marking points Mark s 3(a)(ii) 0.30 mm ≤ d ≤ 0.32 mm. 1 Evidence of repeat readings of diameter expressed to 0.01 mm. 1 3(a)(iii) ● Absolute uncertainty in d in range 0.01 mm (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 expressed to 1 s.f. or 2 s.f. 1 3(a)(iv) A calculated correctly. 1 3(b)(iv) Evidence of repeat readings of timings (repeat twice for timings ≥ 15 s, repeat thrice for 5 s ≤ timings ≤ 15 s). 1 T expressed to the number of significant figures as the timings. 1 3(b)(v) ● Absolute uncertainty in timing in range 0.2 s – 0.5 s (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 expressed to 1 s.f. or 2 s.f. 1 3(c)(i) 0.14 mm ≤ d ≤ 0.16 mm. 1 A calculated correctly. 1 3(c)(ii) Second value of T > first value of T. 1 3(d)(i) Two values of k calculated correctly, expressed to the least significant figures of values used, k correct unit (e.g. cm1.5 s). 1

3 Questio n Marking points Mark s 3(d)(ii) Valid comment consistent with the percentage difference of the values of k and testing against the any one of the two percentage uncertainties in (a)(iii) and (b)(v). 1 Testing percentage difference of the values of k against percentage uncertainty = 2 × (a)(iii) + (b)(iii). 1 3(e)(ii) Varying of m with at least one reading of T greater and one reading smaller than 𝑇𝑆 1 Reasonable method to approx. m eg. Sketch T against m as accurately as possible. 1 m is approximated by showing T = 𝑇𝑆 on the sketched graph. 1 Note: When period T for different m is similar, candidate must have collected the data of swinging oscillation rather than torsional oscillation. This part will be awarded zero. 3(f) Measure diameter of mass with vernier callipers and state radius = diameter / 2. Note: Micrometer screw gauge is not accepted because if r > jaw, instrument cannot be used. 1 Set up the apparatus and follow the procedure in (a) and (b) using mass of at least 6 different radii. Follow the procedure in (a)(iii) and (b) to determine the period T of the (torsional) oscillations. 1 Keep L and m constant when repeating for different radii. 1 Plot a graph of T against r or r against T and state proportionality shown when a straight line through origin obtained. 1 Very small radii has very short period (and difficult to count the number of oscillations). To keep the mass constant, large radii means that the mass must be very thin or very large radii has very long period (and difficult to ascertain the completion of one oscillation). 1

4 Question 4 marking points Marks D1 Diagram ● Labelled diagram, drawn with ruler, with either a table or indicated as top view. ● Equipment must not be “floating”. ● Diagram must include speaker, foam, wooden panel ● Diagram include the apparatus mentioned in the procedure e.g. speaker connected to signal generator, sensor/ microphone/ receiver, CRO, data logger etc. 1 M1 Methods + Instruments to measure dependent variable Measure intensity I (or amplitude) of reflected signal using sound meter or microphone connected to CRO or data logger / sound sensor or sound intensity sensor connected to data logger. The following are not accepted: “power sensor”/ “intensity sensor” 1 M2 M3 M4 M5 Methods + instruments to measure independent. Procedure 1 Vary frequency f with signal generator, t fixed f read directly from signal generator (must mention) or calculate using f = 1/T and measure T from c.r.o. or sound sensor connected to data logger. Note: sound meter/sound intensity meter only measures intensity in dB (unless connected to data logger). Do not accept measurement of frequency using sound meter. Procedure 2 Vary thickness by stacking the foam pieces, fix f Measure the thickness of foam with a rule/ micrometer/ vernier calipers. 4 C1 Control of variables ● Speaker at fixed angle and cannot be normal to the panel ● Fixed distance between speaker to foam and foam to microphone ● Fixed speaker output (loudness, intensity, etc) 1 A1 A2 Method of analysis Procedure 1: Plot a graph of lg Ι vs lg f with gradient is y. Procedure 2: Plot a graph of lg Ι vs lg t with gradient is x. 2 P1 Procedure to reduce interference Valid methods to reduce interference (shown either in procedure or indicated in the diagram) e.g. shielding between speaker and sensor (NOT sound-proof room) or position of sensor ‘behind’ speaker at sufficiently wide angle such that no interference from speaker. 1 Additional detail and/or safety precaution (max 2 marks) AD1 Preliminary reading to ensure intensity can be read by sensor (without distortion) and varied by procedure AD2 Details