Magnets and Magnetism: KS3 Physics Guide

A magnet is an object that produces an invisible magnetic field — a region in which a magnetic force acts on other magnetic materials or moving electric charges. Magnets have two poles (north and south), and the behaviour of those poles follows a simple rule: like poles repel, unlike poles attract. Magnetism is a core KS3 physics topic, covered in Year 7 or Year 8.

What is a magnetic field?

A magnetic field is the region of space around a magnet where a magnetic force can be detected. We represent magnetic fields using field lines (also called flux lines):

Field lines run from the north pole to the south pole outside the magnet.

Where field lines are close together, the field is strong (this is at the poles).

Where field lines are spread apart, the field is weak.

Field lines never cross.

A plotting compass placed near a bar magnet will align itself with the local field line, with the compass needle pointing in the direction a free north pole would move (i.e. away from a north pole, towards a south pole). Moving the compass around the magnet traces out the complete field pattern — this is the classic KS3 practical.

What are magnetic poles?

Every magnet has a north pole and a south pole. The rule for magnetic poles is:

Like poles repel — two north poles or two south poles push each other apart.

Unlike poles attract — a north and a south pole pull each other together.

You cannot isolate a single pole by cutting a magnet in half. If you break a bar magnet in two, each half becomes a complete magnet with its own north and south poles.

Which materials are magnetic?

Not all materials respond to magnetic fields. Materials that are attracted to magnets are called magnetic materials:

Magnetic materials (attracted to magnets) | Non-magnetic materials (not attracted)
Iron | Copper
Steel | Aluminium
Nickel | Plastic
Cobalt | Wood
| Glass

A useful memory check: the four main magnetic metals are iron, steel, nickel, cobalt. Note that steel is an alloy of iron and carbon — its magnetic properties come from its iron content. Copper and aluminium are common metals that are entirely non-magnetic.

What is the difference between permanent and induced magnets?

| Permanent magnet | Induced (temporary) magnet
Definition | Produces its own magnetic field all the time | Becomes magnetised only when placed in a magnetic field
Retains magnetism? | Yes, even when removed from a field | No — loses magnetism when removed from the field
Material | Usually steel (hard magnetic material) | Usually iron (soft magnetic material)
Example | Fridge magnet, bar magnet | Paperclip attracted to a magnet

Steel is used for permanent magnets because it is a "magnetically hard" material — its domains align when magnetised and resist becoming demagnetised. Iron is "magnetically soft" — its domains align easily in a field but return to random orientation when the field is removed.

What is Earth's magnetic field?

Earth behaves like a giant magnet, with a magnetic field that extends far into space. This field is thought to be generated by convection currents of molten iron in Earth's outer core — these moving charges produce a dynamo effect.

A compass works because its needle is a small permanent magnet that aligns with Earth's magnetic field, pointing roughly towards geographic north.

Geographic north and magnetic north are not exactly the same; there is a small angular difference called magnetic declination, which varies by location.

Earth's magnetic field also deflects charged particles from the Sun (the solar wind), protecting life on the surface.

What is an electromagnet?

An electromagnet is a coil of wire (a solenoid) carrying an electric current. When current flows through a wire, it produces a magnetic field around the wire. Winding the wire into a coil concentrates and strengthens this field so that the coil behaves like a bar magnet — with a north and a south pole at either end.

Key advantage: the magnetic field exists only while current is flowing. Switch off the current and the field disappears immediately. This makes electromagnets far more controllable than permanent magnets.

How can you make an electromagnet stronger?

Three methods:

Increase the number of turns (coils) — more coils means more wire contributing to the field at any point.

Increase the current — a larger current through each coil produces a proportionally stronger field.

Add an iron core — placing a soft-iron core inside the coil dramatically amplifies the field because the iron becomes an induced magnet that adds to the electromagnetic field.

Worked example: plotting field lines around a bar magnet

Place a bar magnet flat on a piece of paper. Position a plotting compass near the north pole. Mark the position of the needle's north-end with a dot. Move the compass so its south end sits over the dot just marked, and place a new dot at the north end. Repeat until the compass reaches the south pole of the bar magnet. Connect the dots — you have traced one complete field line. Repeat around the entire magnet to build up the full field pattern, which shows lines emerging from the north pole, curving outward, and re-entering at the south pole.

According to the Department for Education's Science Programmes of Study for Key Stage 3, pupils should learn about magnetic fields, the distinction between permanent and induced magnets, and the principles behind electromagnets. BBC Bitesize KS3 Physics provides diagrams of field line patterns and interactive questions on magnetic forces.

Frequently asked questions

What is the difference between magnetic and non-magnetic materials?

Magnetic materials (iron, steel, nickel, cobalt) contain atoms that behave like tiny magnets and can align their internal structure in response to an external magnetic field. Non-magnetic materials (copper, aluminium, plastic, glass, wood) do not have this property — their atoms do not align in a magnetic field and they experience no attractive force. It is a common mistake to think that all metals are magnetic — copper and aluminium, for example, are metals but are completely non-magnetic.

How do you make an electromagnet stronger?

You can increase an electromagnet's strength in three ways: (1) increase the number of turns of wire in the coil — more turns means more field contributions overlapping; (2) increase the electric current flowing through the wire — a stronger current produces a stronger field per turn; (3) insert a soft-iron core inside the coil — the iron becomes an induced magnet that adds to the overall field, often multiplying the field strength by a factor of hundreds. Changing the type of wire (e.g. copper vs steel) has no significant effect on field strength.

Why do like poles repel?

Magnetic forces arise from the interaction of magnetic fields. When two north poles are brought together, their field lines point in the same direction between the poles and create a region of high-pressure field that pushes the magnets apart. When unlike poles (north and south) meet, the field lines run from north to south and the two fields add together, pulling the magnets towards each other. The underlying physics involves the behaviour of magnetic dipoles — but at KS3 the key rule is simply: like poles repel, unlike poles attract.

What is Earth's magnetic field used for?

Earth's magnetic field has several practical and protective functions. Navigation: compasses align with the field to indicate roughly north, a tool sailors and hikers have relied on for centuries. Protection: the field deflects energetic charged particles from the solar wind (streams of protons and electrons from the Sun), preventing them from stripping away the atmosphere and damaging DNA. Science: geologists study patterns in ancient rocks that recorded Earth's past magnetic field, revealing that the poles have reversed hundreds of times over geological history.

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