A-LevelPhysicsOscillations9702/33 · Oct/Nov 2019 · Q220 Marks

In this experiment, you will investigate the motion of a magnet connected to some springs.

(a)(i)You have been provided with two magnets A and B and three connected springs. • Use the tape to attach magnet A to the springs as shown in Fig. 2.1. [Figure 2.1] • Set up the apparatus as shown in Fig. 2.2, with the N poles of magnets A and B facing each other. [Figure 2.2] The distance between the magnets is x. Adjust the height of the wooden rod until x is approximately 7cm. • Measure and record x. x = [1]
(a)(ii)Estimate the percentage uncertainty in your value of x. percentage uncertainty = [1]
(b)(i)• Pull magnet A down through a short distance. • Release the magnet. The magnet will oscillate. • Determine the period T₁ of these oscillations. T₁ = s [2]
(b)(ii)Reverse magnet B in the G-clamp so that its S pole is at the top. • Adjust the position of the wooden rod until x has the same value as in (a)(i). • Determine the period T₂ of the oscillations of magnet A. T₂ = s [1]
(b)(iii)Calculate T₂ – T₁. T₂ – T₁ = s [1]
(c)• Reverse magnet B so that its N pole is at the top. • Adjust the position of the wooden rod until x is approximately 10cm. • Measure and record x. • Repeat (b) using this value of x. x = T₁ = s T₂ = s T₂ – T₁ = s [3]
(d)(i)It is suggested that the relationship between T₁, T₂ and x is T₂ – T₁ = k / x³ where k is a constant. Using your data, calculate two values of k. first value of k = second value of k = [1]
(d)(ii)Justify the number of significant figures that you have given for your values of k.[1]
(d)(iii)Explain whether your results in (d)(i) support the suggested relationship.[1]
(e)(i)Describe four sources of uncertainty or limitations of the procedure for this experiment. 1. 2. 3. 4.[4]
(e)(ii)Describe four improvements that could be made to this experiment. You may suggest the use of other apparatus or different procedures. 1. 2. 3. 4.[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 2019). The mark or mark type is shown in brackets.

[1] Value of x in the range 6.5–7.5 cm to the nearest mm with unit.
[1] Percentage uncertainty in x based on absolute uncertainty in the range 2–4 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.
[1] Value of T₁ in the range 0.4–1.0 s.
[1] At least two values of nT recorded where n ≥ 5.
[1] Value of T₂ greater than T₁.
[1] Correct calculation of T₂ - T₁.
[1] Second value of x.
[1] Second values of T₁ and T₂.
[1] Quality: Second value of | T₂ – T₁| < first value of | T₂ – T₁|.
[1] Two values of k calculated correctly.
[1] Justification for s.f. in k linked to s.f. in x and (T₂ – T₁).
[1] Valid comment consistent with calculated values of k, testing against a criterion stated by the candidate.
[4] A Too few readings/(only) two readings not enough to draw a (valid) conclusion (not 'not enough for accurate results', 'few readings').
[4] B Problem with attaching spring to magnet e.g. tape not sticky enough, magnet falls from tape or Problems with additional modelling clay falling off magnet.
[4] C Difficult to line up magnets (because they repel).
[4] D Difficulty setting or measuring x with a reason e.g. holding metre rule by hand/metre rule or magnet moves/metre rule not vertical/parallax error/magnet is tilted so x varies across the width of the magnet/difficult to adjust boss so that x has the constant value.
[4] E (T2-T1) is short or Percentage uncertainty in (T2 – T₁) is large or Difficult to judge start of/end of/complete oscillation.
[4] F Others modes of oscillation e.g. magnet swinging or Magnets are attracted/stick to the stand (metal rod) and/or G-clamp/metal table.
[4] A Take more readings and plot a graph or take more readings and compare k values (not 'repeat readings' on its own).
[4] B Better method of attaching magnet to spring system e.g. glue spring to magnet/stickier tape/magnet with hook/attach string or Improved method of adding weight to magnet e.g. use adhesive putty/tape.
[4] C Put magnets in a (transparent) tube.
[4] D Improved method of measuring x e.g. place a mm grid behind magnets/clamp metre rule/use set square between ruler and bench/plumb-line to check ruler vertical/use a lab jack to raise magnet B/use travelling microscope.
[4] E Improved method of timing e.g. video/film/record with timer/view frame-by-frame, fiducial marker at centre of oscillation, force meter attached to springs.
[4] F Use wooden/plastic stand/longer wooden rod or Another named method of fixing magnet B to bench e.g. adhesive putty.