Magnets and magnetic fields

Permanent vs induced magnets

A permanent magnet produces its own magnetic field at all times (e.g. bar magnet, fridge magnet). An induced magnet becomes magnetic only while it is in a magnetic field (e.g. a steel paperclip near a bar magnet); when removed, it loses (most of) its magnetism.

Induced magnets are always attracted to the inducing magnet — they cannot repel.

Magnetic materials

Only iron, steel, cobalt, nickel (and certain alloys) are magnetic. Aluminium, copper, plastic, wood — non-magnetic.

Magnetic poles

Every magnet has a north and south pole — they cannot exist alone (no monopoles).

• Like poles repel (N–N or S–S).
• Unlike poles attract (N–S).

The force between poles is non-contact. It increases as the poles get closer.

Magnetic field

A magnetic field is the region around a magnet where another magnet or magnetic material would feel a force. We represent the field with field lines that:

• Run from N to S outside the magnet.
• Are closer together where the field is stronger (especially at the poles).
• Never cross.

You can map a field with iron filings (sprinkle on paper over the magnet, tap gently — filings line up along field lines) or by walking a small plotting compass around the magnet.

The Earth's magnetic field

A compass needle aligns with the Earth's field — the N pole of the compass points to (geographic) magnetic North. This means the Earth's geographic North is actually a magnetic south pole (because unlike poles attract). The field is generated by movement of molten iron in the Earth's core.

Edexcel exam tip

When asked to "describe the magnetic field around a bar magnet", award marks fall in this exact order: arrows from N to S outside the magnet M1; curves not straight lines B1; closer together at poles → stronger field B1. Always include arrowheads on diagrams.