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IB · D · multiple choice

Fields · Question 5

Fields · Original GioPhysics question with a detailed, mark-by-mark answer guide.

Demand
demanding
Marks
1
Topics
1
Answer
Complete
A bar magnet falling north pole downward towards a copper ringSNbar magnetvcopper ring
Figure 3Side view. A bar magnet is drawn vertically above a horizontal copper ring, with its two halves marked S at the top and N at the bottom, so that the north pole is the end facing the ring. An arrow beside the magnet, labelled v, points vertically downward. A faint dashed line continues from the bottom of the magnet straight down through the centre of the ring, which is drawn as a flattened ellipse to show it lying horizontally, and is labelled 'copper ring'.
multiple choice1 mark

A bar magnet is dropped, north pole downward, through a horizontal copper ring. Which describes the force on the magnet as it approaches the ring and after it has passed through?

  1. A

    upward as it approaches, upward after it has passed

  2. B

    upward as it approaches, downward after it has passed

  3. C

    downward as it approaches, upward after it has passed

  4. D

    there is no force, because copper is not magnetic

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Answer overviewCorrect answer: A — upward as it approaches, upward after it has passed
01

Answer and reasoning

1 mark
How to approach it

Predict from the governing principle before looking for a matching option. Then reject alternatives by checking direction, units, limiting behaviour or the physical meaning of each statement.

  1. 1

    The correct choice is A: upward as it approaches, upward after it has passed

  2. 2

    B is the intuitive answer — the ring appears to repel then attract — but Lenz's law makes the induced effect oppose the motion in both stages. Approaching, the ring repels; receding, it attracts; and both act upward on a falling magnet. D confuses ferromagnetism with induction.

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