A-LevelPhysicsOscillations9702/31 · May/June 2018 · Q220 Marks

In this experiment, you will investigate the oscillations of a magnet.

(a)You have been provided with a metal plate. • Use tape to secure the plate at the edge of the bench as shown in Fig. 2.1. • Use more tape to secure one of the paper strips to the bench so that it covers the plate, as shown in Fig. 2.2. You have been provided with a bar magnet attached to a string. • Set up the apparatus as shown in Fig. 2.3. • The distance between the bottom of the split cork and the bottom of the magnet should be approximately 55 cm. • The distance between the bottom of the magnet and the paper strip is x. Adjust the height of the magnet so that x is approximately 3mm. • Measure and record x.[1]
(b)• Move the stand until the magnet hangs with one edge vertically above line A, as shown in Fig. 2.4. • Pull the magnet to the right, keeping the string straight, until the same edge of the magnet is above line B, as shown in Fig. 2.5. • Release the magnet. The magnet will oscillate. • Draw a line on the paper at the position of the edge of the magnet after 30 complete oscillations. • Label this line C. The distance BC is y as shown in Fig. 2.6. • Measure and record y.[2]
(c)Estimate the percentage uncertainty in your value of y.[1]
(d)• Increase x to approximately 8 mm. • Measure and record x. • Repeat (b).[3]
(e)(i)It is suggested that the relationship between y and x is k y = — √x where k is a constant. Using your data, calculate two values of k.[1]
(e)(ii)Explain whether your results support the suggested relationship.[1]
(f)(i)• Remove the plate and paper strip from the bench. Do not adjust the height of the magnet above the bench. • Using the second strip of paper, repeat (b) without the plate.[1]
(f)(ii)Using your second value of k, calculate x when y has the value given in (f)(i).[1]
(f)(iii)Justify the number of significant figures that you have given for your value of x in (f)(ii).[1]
(g)(i)Describe four sources of uncertainty or limitations of the procedure for this experiment.[4]
(g)(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 (May/June 2018). The mark or mark type is shown in brackets.

[1] Value of x with unit and in the range 1.0-5.0 mm.
[1] All value(s) of raw y to nearest mm with unit.
[1] Evidence of repeat values of y.
[1] Absolute uncertainty in y 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.
[1] Correct method of calculation to find percentage uncertainty.
[1] Second value of x.
[1] Second value of y.
[1] Quality: second value of y < first value of y.
[1] Two values of k calculated correctly.
[1] Valid comment consistent with the calculated values of k, testing against a criterion stated by the candidate.
[1] Value of y.
[1] Correct calculation of x.
[1] Justification for s.f. in x linked to s.f. in y.
[1] Two readings are not enough to draw a (valid) conclusion (not "not enough for accurate results”, “few readings").
[1] Difficulty with alignment at A with a reason e.g. string twists/magnet will not settle/magnet continually moves/draughts or air conditioning disturb magnet.
[1] Difficulty in finding position C or position after 30 oscillations or finding y with a reason e.g. magnet only stays at position C for a short time/difficult to estimate where magnet will stop/difficult to judge the end of an oscillation/parallax.
[1] Difficulty linked to x with a reason e.g. metre rule (too large or not precise enough/large percentage uncertainty in x/value of x is small/ adjustment difficult or clumsy with clamp and cork/angled lower surface of magnet.
[1] Difficulty with the oscillation e.g. magnet rotates while swinging/wrong mode of oscillation/magnetic stand attracts the magnet affecting its motion.
[1] Take many readings and plot a graph or take more readings and compare k values (not “repeat readings" on its own).
[1] Improved method of alignment with A e.g. valid improvement to suspension e.g. nylon thread/wire/double point of suspension/switch off AC/windshield.
[1] Improved method of locating C e.g. use a scale/use of a pointer with detail of how pointer is used e.g. attached to magnet/use to refine position of C.
[1] Improved method to adjust x e.g. scissor jack/rearrange suspension to use screw thread on clamp.
[1] Improved method to measure x e.g. travelling microscope/vernier or digital calipers/use of thin spacers e.g. sheets of paper/shim.
[1] Use a wooden or plastic stand i.e. a named non-magnetic material.