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Magnetism

Key idea: O Level magnetism: classify magnetic materials and predict attraction or repulsion from the poles that face each other.

  • SEC G3 Physics 2027
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Learning objectives

  • State the properties of magnets
  • Describe induced magnetism
  • Distinguish temporary and permanent magnets
  • Determine magnetic-field direction with a compass or bar magnet
  • Interpret bar-magnet field patterns
  • Draw the magnetic field pattern around a bar magnet and between the poles of two bar magnets
  • Interpret the field pattern around a straight current-carrying wire
  • Draw the magnetic field pattern around a straight current-carrying wire
  • Interpret the field pattern around a current-carrying solenoid
  • Draw the magnetic field pattern around a current-carrying solenoid
  • Relate current magnitude and direction to magnetic field
  • Describe electromagnet applications
  • Describe experiments showing the force on a current-carrying conductor in a magnetic field
  • Describe magnetic force on a charged-particle beam
  • Predict force reversal when current or field reverses
  • Use Fleming’s left-hand rule
  • Explain the turning effect on a current-carrying coil
  • Explain how current and turns increase the turning effect
  • Describe split-ring commutator action
  • Describe the effect of winding a motor coil on a soft-iron cylinder
  • Deduce that a changing magnetic field can induce an e.m.f.
  • Deduce that induced e.m.f. opposes the change producing it
  • Deduce factors affecting induced e.m.f. magnitude
  • Describe a simple a.c. generator and slip rings
  • Sketch a simple a.c. generator voltage–time graph
  • Describe a simple iron-cored transformer
  • Apply ideal-transformer equations
  • Explain cable loss and high-voltage transmission

1. Definitions

Magnetism is an interaction that can produce attraction or repulsion between magnets. A magnet can also attract an unmagnetised magnetic material.

This lesson focuses on classifying materials and predicting forces. Continue to Properties of magnets for the sure test, compass alignment and what happens when a magnet is cut.

2. Key Ideas

  • Every bar magnet has a north pole (N) and a south pole (S).
  • Unlike poles attract; like poles repel. Read the two facing ends before deciding the force.
  • A magnet attracts an unmagnetised magnetic material, whichever pole is brought near it.
  • Common magnetic materials at O Level include iron, steel, nickel and cobalt.
  • Copper and aluminium are metals, but they are not classified as magnetic materials in this context.
Magnetic interactions and material attractionThree comparisons show unlike poles attracting, like poles repelling, and a magnet attracting an unmagnetised iron bar. A final panel shows that cutting a bar magnet produces two smaller magnets, each with north and south poles.Read the facing ends firstUnlike polesNSattractForce is towards the gap.Like polesNNrepelForce is away from the gap.Magnet + ironNironalso attractsInduced magnetism makes thenear end an opposite pole.Cutting does not isolate one poleNScutN SN Seach piece has both polesSure-test conclusionUse the same known pole atboth ends of the unknown bar.Repulsion at either end:unknown is a magnetAttraction at both ends:could be unmagnetised iron
Scroll diagram horizontally to read all labels.
Unlike poles attract and like poles repel. Attraction is inconclusive because an unmagnetised iron bar is also attracted; observed repulsion with a known magnet proves the unknown is a magnet.

3. Detailed Explanations

Use this two-step method:

  1. Decide whether both objects are magnets. If one is an unmagnetised iron or steel object, predict attraction.
  2. If both are magnets, identify the facing poles: N–S attracts, while N–N and S–S repel.

The force arrows in a diagram should point towards the gap for attraction and away from the gap for repulsion.

Magnetic does not mean magnetised

An iron nail is a magnetic material, but it is not necessarily a magnet. Near a magnet, induced magnetism can make the nail attract. Learn how the nearer end acquires the opposite pole in Induced magnetism.

4. Common Mistakes

  • “Magnets attract all metals.” Copper and aluminium provide standard counterexamples.
  • “A north pole always repels.” It repels another north pole but attracts a south pole or an unmagnetised magnetic material.
  • “If an object is attracted, it must be a magnet.” Attraction also occurs through induced magnetism.
  • “Magnetic material” means “already magnetised”. It describes a material that can be magnetised and attracted strongly by a magnet.

5. Exam Tips

  1. Name both facing poles before stating attraction or repulsion.
  2. When classifying an object, distinguish the material from its current magnetisation.
  3. If attraction is the only observation, do not conclude that the unknown object is a magnet.

6. Worked Examples

Modelled example 1

Facing poles

Core

Problem

The north pole of one bar magnet faces the south pole of another. Predict the force on each magnet.
Study the worked solution

  1. Identify the facing poles

    Method

    Name the two poles across the gap: north and south.

    Reason

    The interaction rule depends on the poles that face, not on the magnets’ other ends.

    Working

    The facing poles are unlike.

  2. Apply the pole rule

    Method

    Use “unlike poles attract”.

    Reason

    Each magnet experiences a force towards the other magnet.

    Working

    Both forces point towards the gap, so the magnets attract.

Common misconception 2

A metal object

Find and correct the mistake

Learner claim

A bar is attracted to either pole of a known magnet. A learner concludes that the bar must be a magnet. Locate the first error and correct the conclusion.

Test the claim

First error

View solution step by step

  1. Identify the alternative explanation

    Method

    Recognise that unmagnetised iron can be attracted to either pole.

    Reason

    The known magnet induces temporary magnetism in the material.

    Working

    Attraction alone is therefore inconclusive.

  2. Limit the conclusion

    Method

    State only that the bar is made from a magnetic material or may itself be a magnet.

    Reason

    Either possibility can explain attraction, so this observation cannot distinguish them.

    Working

    Correct conclusion: attraction alone does not prove that the bar is a magnet.

Challenge 3

Classifying materials

Minimal support

Classification transfer

Classify iron, copper, steel and aluminium as magnetic or non-magnetic in the O-Level model.

Classify before revealing

Hints

Hint 1: separate material from magnetisation
A material can be magnetic even when it is not currently a magnet.
View solution step by step

  1. Classify the magnetic materials

    Method

    Place iron and steel in the magnetic group.

    Reason

    They can be magnetised and are strongly attracted by a magnet in the course model.

    Working

    Magnetic: iron, steel.

  2. Classify the remaining materials

    Method

    Place copper and aluminium in the non-magnetic group.

    Reason

    They are treated as non-magnetic in this O-Level classification.

    Working

    Non-magnetic: copper, aluminium.

7. Mind Stretchers

Open the Bar magnet mode in the Magnetism and Induction Lab. Predict the compass north-end direction at labelled probes near a pole and farther away before checking. This checks field direction; it does not by itself test whether an unknown bar is a magnet.

Then sort these objects into “magnetic material” and “not magnetic in this course model”: iron nail, steel paperclip, copper wire and aluminium foil. Explain why belonging to the first group does not mean an object is already magnetised.

8. Practice, Quiz and Next Step

Practise pole interactions and material classification in the Magnetism Quiz, then continue to Properties of Magnets for the experimental sure test.

Continue with the next resource in this course.

Course and syllabus information
Course
SEC G3 Physics
Edition
SEC G3 Physics 2027