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Date	May 2022	Marks available	1	Reference code	22M.2.HL.TZ2.8
Level	Higher level	Paper	Paper 2	Time zone	2
Command term	State	Question number	8	Adapted from	N/A

Question

A fixed horizontal coil is connected to an ideal voltmeter. A bar magnet is released from rest so that it falls vertically through the coil along the central axis of the coil.

The variation with time t of the emf induced in the coil is shown.

Write down the maximum magnitude of the rate of change of flux linked with the coil.

[1]

a.i.

State the fundamental SI unit for your answer to (a)(i).

[1]

a.ii.

Explain why the graph becomes negative.

[3]

b.i.

Part of the graph is above the t-axis and part is below. Outline why the areas between the t-axis and the curve for these two parts are likely to be the same.

[2]

b.ii.

Predict the changes to the graph when the magnet is dropped from a lower height above the coil.

[3]

Markscheme

«−» 5.0 «mV» OR 5.0 × 10⁻³ «V» ✓

Accept 5.1

a.i.

kg m²A⁻¹s⁻³ ✓

a.ii.

ALTERNATIVE 1

Flux linkage is represented by magnetic field lines through the coil ✓

when magnet has passed through the coil / is moving away ✓

flux «linkage» is decreasing ✓

suitable comment that it is the opposite when above ✓

when the magnet goes through the midpoint the induced emf is zero ✓

ALTERNATIVE 2

reference to / states Lenz’s law ✓

when magnet has passed through the coil / is moving away ✓

«coil attracts outgoing S pole so» induced field is downwards ✓

before «coil repels incoming N pole so» induced field is upwards
OR
induced field has reversed ✓

when the magnet goes through the midpoint the induced emf is zero ✓

OWTTE

b.i.

area represents the total change in flux «linkage» ✓

the change in flux is the same going in and out ✓

«when magnet is approaching» flux increases to a maximum ✓

«when magnet is receding» flux decreases to zero ✓

«so areas must be the same»

b.ii.

magnet moves slower ✓

overall time «for interaction» will be longer ✓

peaks will be smaller ✓

areas will be the same as before ✓

Allow a graphical interpretation for MP2 as “graph more spread out”

Examiners report

ai
Well answered, with wrong answers stating 8 for the difference or 3 without realising that the sign does not matter.

aii
Very few candidates managed to get the correct fundamental SI unit for V. All kinds of errors were observed, from power errors to the use of C as a fundamental unit instead of A.

bi) Most scored best by marking using an alternative method introduced to the markscheme in standardisation. There were some confused and vague comments. Clear, concise answers were rare.

bii) It was common to see conservation of energy invoked here with suggestions that energy was the area under the graph. Many candidates described the shapes to explain why the areas were the same rather than talking about the physics e.g. one peak is short and fat and the other is tall and thin so they balance out.

c) A surprising number didn't pick up on the fact that the magnet would be moving slower. As a result, they discussed everything happening sooner, i.e. the interaction with the magnet and the coil, and that led onto things happening quicker so peaks being bigger.

a.i.

[N/A]

a.ii.

[N/A]

b.i.

[N/A]

b.ii.

[N/A]