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Learn0625Papers 1, 3 · CoreElectricity and magnetismMagnetism and magnetic fields
Electricity and magnetism · Subtopic 1 of 8

Magnetism and Magnetic Fields

Magnets have a north and a south pole: like poles repel, unlike poles attract. Magnets attract magnetic materials (iron, steel, nickel, cobalt) by inducing magnetism in them. The space around a magnet where a force acts is its magnetic field, shown by field lines from N to S. Soft iron makes temporary magnets; steel makes permanent ones.

Cambridge 5054 Paper 1Cambridge 5054 Paper 2Cambridge 0625 Papers 2, 4Cambridge 0625 Papers 1, 3Edexcel 4PH1 Paper 1PEdexcel 4PH1 Paper 2P≈ 25 minRevision 5 · updated 2026-10-27
Section 1 of 14

Learning objectives

  • Describe the forces between poles and between magnets and magnetic materials.
  • Explain induced magnetism.
  • Draw and interpret magnetic field lines, and plot them with a compass.
  • Compare soft iron and steel, and give uses of permanent magnets and electromagnets.
Pause and think

A magnet picks up an iron paper clip, and that paper clip can pick up another one. But neither clip was a magnet before. What happened?

Section 2 of 14

Core idea

Start hereA crane that drops its load

A scrapyard crane lifts cars with a huge magnet, then drops them by switching it off. That only works with an electromagnet made of soft iron, which loses its magnetism instantly. A steel core would cling on.

The big idea

Like poles repel; unlike attract. Field lines go N to S; closer lines mean a stronger field. Soft iron: easily magnetised and demagnetised. Steel: keeps magnetism.

1. Fields

Field lines around a bar magnet
SN
Lines leave the N pole and enter the S pole. They are closest together (strongest field) near the poles. Lines never cross.
  • Plot with a compass or iron filings.
  • Induced magnetism: a magnet makes nearby iron temporarily magnetic (so iron is always attracted).

2. Making and destroying magnets

  • Magnetise: stroke with a magnet, or place in a solenoid with d.c.
  • Demagnetise: heat, hammer, or withdraw slowly from a solenoid with a.c.
Worked exampleChoosing materials

An electromagnet core and a permanent magnet.

Goal
Material for each.
Strategy
Match the property needed.

  1. Electromagnet core: soft iron, so the magnetism disappears when switched off.

  2. Permanent magnet: steel, which keeps its magnetism.

AnswerSoft iron; steel.
✓ CheckThe crane needs to release its load ✓.
Common misconceptionAttraction proves a magnet Iron is attracted by either pole. Only repulsion proves both objects are magnets.
Pause and think

How can you tell a magnet from an iron bar?

Summary

  • N to S field lines.
  • Soft vs hard magnetic materials.
Key words
Magnetic field
Region where magnetic forces act.
HistoryLodestones and compasses. Naturally magnetic rocks called lodestones were known in ancient Greece and China. By about 11001100, Chinese navigators were using magnetised needles to find direction at sea, and the compass spread along trade routes to the Arab world and Europe.
Fun factThe Earth is a giant magnet with a twist. A compass's N pole points to the Earth's geographic North Pole, so the magnetic pole up there must be a south pole. The Earth's magnetic field also flips direction every few hundred thousand years; the last flip was about 780 000780\,000 years ago.
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