AHS 2025 Physics P3 MS

2025 Physics Prelim Practical Exam Mark Scheme Q1(minus 1 mark maximum for precision, unit and sf respectively) (a) (i) VT = 11.5 cm3 [1] (to nearest 0.5 cm3 and between 9.0 to 15.0 cm3) (ii) V1 = 1.92 cm3 [1] ((a)(i) ÷ 6 with correct unit and sf) (b) (i) l = 15.0 cm [1] (in cm ± 0.2 cm from supervisor value to the nearest 0.1 cm) (ii) D = 2.1 cm [1] (± 0.3 cm to the nearest 0.1 cm) (iii) d = 0.53 cm [1] ((b)(ii) ÷ 4 with correct unit and sf) (iv) correct use of set squares at each end lined up with rule or correct diagram accept: reject: (v) V2 = 3.3 cm3 [2] (correct calculation, answer in cm3 and rounded off to 2 s.f.) (c) Any 2: • air bubbles in the straw in method 1 • internal volume is smaller than external volume • straw became squashed / damaged • small amount of water may remain in the straw • water sticks to the finger • some water falls out during transfer in method 1 • straw not completely filled ● the measuring cylinder is not dry / there is some water in the measuring cylinder D D or D Set squares may go under the straw

Q2 (minus 1 mark maximum for precision, unit and sf respectively) (a) L = 16.5 cm [1] (to nearest 0.1 cm) (actual values may vary) (b) It is difficult to determine the centre of the adhesive putty as the putty is not uniform. OR: It is difficult to determine the centre of the spring as the adhesive putty is covering it. Reject: the rod is not vertical Reason: The ruler used to measure L need not be vertical. (c) Any 1: ● there is a weight / weights placed on each base ● bosses are attached as low as possible ● d is not too large / the spring is not too stretched (d) Show evidence of at least 5 oscillations and repeating the experiment twice to obtain the average reading. [1] T = 0.785 s [1] (correct unit & s.f.) Example: Average time for 5 oscillations = 3.94 + 3.91 / 2 = 3.93 s. T = 3.93 / 5 = 0.785 s (e) Planning 1 m for each of the 5 bullet points: 1. Identify d and L to be kept constant respectively for 2 experiments [1] 2. Includes taking average timing and repeating for 5 different sets of values (specify by how much) (Plot a graph of dv against iv is marked together with bullet 3) 3. Sketch both graphs correctly (correct shape and axes). [1] 4. Value of a correctly explained in both experiments. [1] *If student only performs one experiment, the maximum mark is 2 out of 4. 5. Explanation for precaution: any one of the following [1] (i) View the oscillation of the rod from above and use the middle of the oscillation (fiducial marker). This is to determine accurately the start and end of an oscillation. (ii) Take the time taken for 5 / 10 oscillations to reduce error due to human reaction time. (iii) Take average readings to reduce unpredictable error. (iv) The amplitude / angle of oscillation must not be too large (less than 10o). This is to ensure that the equation is valid.

Experiment 1: Keep d constant Procedure Step 1: Setup the apparatus shown in Fig 2.2. Let L = 16.0 cm and determine the period T of the oscillating rod as described in procedure 2(d). Step 2: Repeat step 1 to get an average value of T. Step 3: Repeat steps 1 to 2 for 5 more sets of readings by decreasing the length L by 1.0 cm each time. Step 4: Calculate T2 and tabulate all readings. Step 5: Plot a graph of T2 against L (accept T2 against L / d since d is a constant) Sketch of graph: gradient = a / d a = gradient x d (accept a = gradient of graph of T2 against L / d) Experiment 2: Keep L constant Procedure Step 1: Setup the apparatus shown in Fig 2.2. Let d = 26.0 cm and determine the period T of the oscillating rod as described in procedure 2(d). Step 2: Repeat step 1 to get an average value of T. Step 3: Repeat steps 1 to 2 for 5 more sets of readings by decreasing the length d by 1.0 cm each time. Step 4: Calculate T2 and tabulate all readings. Step 5: Plot a graph of T2 against 1/d (accept T2 against L / d since L is a constant) Sketch of graph: gradient = aL a = gradient / L (accept a = gradient of graph of T2 against L / d) T2 / s2 L / cm 0 T2 / s2 1/d / cm-1 0

The values of a from both graphs should be the same. Q3 (minus 1 mark maximum for precision, unit and sf respectively) (b) Vs = 4.50 V [1] (to the nearest 0.05 V; reject values larger than 4.50 V) (Values larger than 4.50 V indicates that the switch is not closed.) (c) (i) θ at least 70.0 ºC [1] 0.50 V < VAB < 2.50 V [1] (ii) θ / oC VAB / V Vt / V I / A Rt / Ω 82.0 1.85 2.95 0.0394 74.9 78.0 1.80 3.00 0.0383 78.3 74.0 1.70 3.10 0.0362 85.7 70.0 1.45 3.35 0.0309 109 66.0 1.35 3.45 0.0287 120 62.0 1.25 3.55 0.0266 134 58.0 1.10 3.70 0.0234 158 54.0 1.00 3.80 0.0213 179 50.0 0.90 3.90 0.019 200 θ / oC VAB / V Vt / V I / A Rt / Ω 77.0 1.65 3.15 0.0351 89.7 74.0 1.55 3.25 0.0330 98.5 71.0 1.50 3.30 0.0319 103 68.0 1.40 3.40 0.0298 114 65.0 1.30 3.50 0.0277 127 62.0 1.20 3.60 0.0255 141 59.0 1.10 3.70 0.0234 158 56.0 1.00 3.80 0.0213 179 53.0 0.95 3.85 0.020 190 50.0 0.90 3.90 0.019 200 ● headings + units in the top row [1] ● at least 8 readings including the readings from part (i)[1] ● Vt = Vs – VAB calculated in column 3 and I = VAB ÷ 47 calculated in column 4 [1] ● Rt = Vt ÷ I calculated in column 5 [1] ● the resistance increases with decreasing temperature [1] ● correct precision for θ and VAB [1] (ecf if precision error already deducted in earlier part)

● correct d.p. for Vt and s.f. for I and Rt [1] (ecf if sf error already deducted in earlier part) (d)(i) ● Axes labelled with units and correct orientation [1] ● Suitable scale, ⩾ ½ page in both directions [1] ● Two points plotted correctly (check two points) [1] ● best fit curved line and fine points or crosses [1] (ii) ● tangent at 65 ºC [1] ● calculation of gradient to 2 or 3 s.f. [1] ● dotted triangle with one side at least five cm long [1] (can review) (e) Make sure the thermistor is fully submerged at all times so that the temperature measured by the thermometer is the same as the temperature of the thermistor. OR: Stir the water to ensure that the temperature measured by the thermometer is the same as the temperature of the thermistor. OR: Position the eye such that the line of sight is level with the (bottom of the) meniscus and at right angles with the thermometer scale to prevent parallax error. (reject at eye level) OR: To prevent parallax error, place the eye at right angles with the ammeter and voltmeter scales such that the image of the pointer in the mirror is covered by the pointer. (f) Any 2: ● The thermometer is touching the beaker / too far from the thermistor, hence it may not be measuring accurately the temperature of the thermistor. ● The amount of hot water that is removed may not be the same as the amount of cooler water that replaces it (as the dropping pipette has no markings). (unable to carry out the procedure on page 10 - replacing removed hot water with a similar volume of cold water) ● It is difficult to look at both the voltmeter and thermometer at the same time, hence the temperature and voltage recorded may not be accurate. ● The circuit is switched on for a long period of time. The resistor heats up and its resistance changes ( no longer 47 Ω). This affects the accuracy of the calculation of current I ( I = VAB / 47). ● The circuit is switched on for a long time causing the value of Vs to decrease. Hence the calculation of Vt and Rt will not be accurate. Reject parallax error as it is not a procedure