A-LevelPhysicsPhysical quantities and units9702/31 · Oct/Nov 2021 · Q220 Marks

In this experiment, you will investigate the flow of oil.

(a)(i)Measure and record the length l of the shorter straw.[1]
(a)(ii)The diameter D of the straw is shown in Fig. 2.1. [Figure 2.1] Measure and record D.[1]
(a)(iii)Calculate the volume V of the straw using V = πD²l / 4[1]
(a)(iv)Justify the number of significant figures that you have given for your value of V.[1]
(b)(i)Draw a circle of radius 2.0 cm on the blank sheet of paper. • Place a Petri dish on top of the circle on the paper. • Use small pieces of adhesive putty at the edge of the Petri dish to secure it to the paper. • Place a small piece of adhesive putty at the centre of the Petri dish. • Gently press the straw into the adhesive putty so that the bottom of the straw is sealed by the putty. • Arrange the apparatus as shown in Fig. 2.2 and Fig. 2.3 with the straw above the centre of the circle drawn on the paper. [Figure 2.2] [Figure 2.3] • You have been provided with plastic gloves to wear when handling the oil. Use the dropper to fill the straw with oil. • When the straw is lifted from the putty, the oil spreads out. The time taken for the first part of the oil to reach the circle is t. • Gently lift the straw away from the putty. Measure and record t.[2]
(b)(ii)Estimate the percentage uncertainty in your value of t. Show your working.[1]
(c)Repeat (a)(i), (a)(iii) and (b)(i) using the longer straw.[3]
(d)(i)It is suggested that the relationship between V and t is V = k / √t where k is a constant. Using your data, calculate two values of k.[1]
(d)(ii)Explain whether your results support the suggested relationship.[1]
(e)(i)Describe four sources of uncertainty or limitations of the procedure for this experiment.[4]
(e)(ii)Describe four improvements that could be made to this experiment. You may suggest the use of other apparatus or different procedures.[4]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (Oct/Nov 2021). The mark or mark type is shown in brackets.

[1] (a)(i) Final value of l with unit and in the range 3.0–3.4 cm.
[1] (a)(ii) Value(s) of raw D all to nearest 0.01 cm or all to nearest 0.001 cm and final value of D with unit and less than 1.0 cm.
[1] (a)(iii) Correct calculation of V.
[1] (a)(iv) Justification for significant figures in V linked to number of s.f. in D and l.
[1] (b)(i) Value of time t > 1.0 s with unit.
[1] (b)(i) Evidence of repeated values of t.
[1] (b)(ii) Percentage uncertainty based on an absolute uncertainty in t in the range 0.2–5 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 find percentage uncertainty.
[1] (c) Second value of l.
[1] (c) Second value of t.
[1] (c) Second value of t is less than first value of t.
[1] (d)(i) Two values of k calculated correctly. The final k values must not be written as fractions.
[1] (d)(ii) Valid comment consistent with the calculated values of k, testing against a criterion stated by the candidate.
[1] (e)(i) A Two readings are not enough to draw a (valid) conclusion (not “not enough for accurate results”, “few readings”).
[1] (e)(i) B Difficulty in measuring time t with a reason (at the start or at the finish) e.g. lifting straw and starting stopwatch simultaneously/judging or predicting when to stop timing.
[1] (e)(i) C Difficulty linked to oil with detail e.g. difficult to see as colourless/clear/transparent or some oil left in straw drips out later/oil leaks from straw/paper straw absorbs oil.
[1] (e)(i) D Difficulty linked to raising or positioning the straw e.g. not always in centre/hand moves when lifted/straw tilted/putty obscures the centre.
[1] (e)(i) E Problem with volume V with reason e.g. D is the external diameter/no account of thickness of straw/squashing straw/putty goes up straw/oil left in straw.
[1] (e)(ii) A Take more readings and plot a graph or take more readings and compare k values (not “repeat readings" on its own).
[1] (e)(ii) B Improved method to measure t e.g. video/film/ record with timer/view frame by frame.
[1] (e)(ii) C Improved method to see oil e.g. add dye or improved method to contain the oil e.g. flap/cap/plastic straw.
[1] (e)(ii) D Improved method to release or positioning of straw e.g. clamp a laser with beam above the centre point/clamp a guide at the centre/draw a cross on the paper.
[1] (e)(ii) E Valid method to measure internal straw diameter e.g. travelling microscope or method to measure thickness directly e.g. cut open and use micrometer to measure wall thickness.