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Date May 2019 Marks available 2 Reference code 19M.2.HL.TZ2.10
Level Higher level Paper Paper 2 Time zone 2
Command term Deduce Question number 10 Adapted from N/A

Question

A small magnet is dropped from rest above a stationary horizontal conducting ring. The south (S) pole of the magnet is upwards.

While the magnet is moving towards the ring, state why the magnetic flux in the ring is increasing.

[1]
a.

While the magnet is moving towards the ring, sketch, using an arrow on Diagram 2, the direction of the induced current in the ring.

[1]
b.

While the magnet is moving towards the ring, deduce the direction of the magnetic force on the magnet.

[2]
c.

Markscheme

the magnetic field at the position of the ring is increasing «because the magnet gets closer to the ring» ✔

a.

the current must be counterclockwise «in diagram 2» ✔

eg:

b.

since the induced magnetic field is upwards

OR

by Lenz law the change «of magnetic field/flux» must be opposed

OR

by conservation of energy the movement of the magnet must be opposed ✔

therefore the force is repulsive/upwards ✔

c.

Examiners report

This was well-answered.

a.

Answers here were reasonably evenly split between clockwise and anti-clockwise, with the odd few arrows pointing left or right.

b.

The majority of candidates recognised that the magnetic force would be upwards and the most common way of explaining this was via Lenz’s law. Students needed to get across that the force is opposing a change or a motion.

c.

Syllabus sections

Additional higher level (AHL) » Topic 11: Electromagnetic induction » 11.1 – Electromagnetic induction
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Additional higher level (AHL) » Topic 11: Electromagnetic induction
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