Poles and Magnetic Fields

Magnetism is one of the fundamental forces in physics. In this lesson you will learn about magnetic poles, magnetic fields and how to represent them using field lines. This topic forms the foundation of Chapter 4.7 (Magnetism and Electromagnetism) of the AQA GCSE Physics specification.

What Is a Magnet?

A magnet is an object that produces a magnetic field around itself. Magnets attract certain materials, most notably iron, steel, cobalt and nickel. These materials are called magnetic materials (or ferromagnetic materials).

Materials that are not attracted to magnets, such as wood, plastic and copper, are called non-magnetic materials.

Property	Magnetic Materials	Non-Magnetic Materials
Attracted to magnets	Yes	No
Examples	Iron, steel, cobalt, nickel	Wood, plastic, copper, aluminium
Can be magnetised	Yes	No

Exam Tip: A common mistake is to say that all metals are magnetic. Only iron, steel, cobalt and nickel are magnetic at GCSE level. Copper, aluminium and gold are metals but they are NOT magnetic.

Magnetic Poles

Every magnet has two poles: a north pole (N) and a south pole (S). The magnetic field is strongest at the poles.

Rules of Magnetic Attraction and Repulsion

Like poles repel — two north poles or two south poles push each other away.
Unlike poles attract — a north pole and a south pole pull each other together.

Combination	Result
N — N	Repel
S — S	Repel
N — S	Attract
S — N	Attract

Exam Tip: The rule "like poles repel, unlike poles attract" is one of the most tested facts in the magnetism topic. If you see a question about two magnets interacting, identify the facing poles first.

Permanent and Induced Magnets

There are two types of magnet you need to know:

Permanent Magnets

A permanent magnet produces its own magnetic field. It does not need an external source of energy. Examples include bar magnets and horseshoe magnets. A permanent magnet always has a north and a south pole.

Induced Magnets

An induced magnet is a material that becomes magnetic only when it is placed in a magnetic field. When the external magnetic field is removed, the induced magnet loses most or all of its magnetism.

Feature	Permanent Magnet	Induced Magnet
Source of magnetism	Own internal magnetic field	External magnetic field
Retains magnetism	Yes — always magnetic	No — loses magnetism when field removed
Poles	Fixed N and S	Temporary; nearest pole is always opposite to the permanent magnet
Force	Can attract or repel	Always attracts the permanent magnet

Exam Tip: Induced magnets are ALWAYS attracted to the permanent magnet that is inducing them. They never repel. This is because the nearest pole of the induced magnet is always the opposite pole to the permanent magnet.

Magnetic Fields

A magnetic field is the region around a magnet where a force acts on another magnet or on a magnetic material. The magnetic field is invisible, but we can represent it using magnetic field lines.

Properties of Magnetic Field Lines

Field lines always go from north to south (outside the magnet).
Field lines never cross each other.
The closer together the field lines, the stronger the magnetic field.
The field is strongest at the poles where the lines are closest together.

graph LR
    subgraph "Bar Magnet Field Lines"
        N["N pole"] -->|"Field lines go from N to S"| S["S pole"]
    end
    style N fill:#ff6666,stroke:#cc0000
    style S fill:#6666ff,stroke:#0000cc

Plotting Magnetic Field Lines

You can map out a magnetic field using a plotting compass:

Place the bar magnet on a sheet of paper.
Place a small plotting compass near the north pole of the magnet.
Mark a dot at the position of the compass needle tip (the end pointing away from the north pole).
Move the compass so the tail of the needle is on the dot you just drew.
Mark another dot at the new position of the needle tip.
Repeat until you reach the south pole of the magnet.
Join the dots to form a smooth curved field line.
Add an arrow pointing from north to south.
Repeat for several starting positions to build up the full field pattern.

Uniform and Non-Uniform Fields

Field Type	Description	Field Lines
Non-uniform	Field strength varies from place to place (e.g., around a bar magnet)	Curved, spacing varies
Uniform	Field strength is the same everywhere in the region	Parallel, equally spaced

A uniform field exists between two flat, parallel magnets of opposite poles facing each other. The field lines are straight, parallel and evenly spaced.

The Magnetic Field of the Earth

The Earth behaves as if it has a giant bar magnet inside it. The Earth has a magnetic field that:

Has a magnetic north pole near the geographic south pole and a magnetic south pole near the geographic north pole.
Causes compass needles to align roughly north-south.
Protects the Earth from charged particles in the solar wind.

graph TD
    subgraph "Earth's Magnetic Field"
        GN["Geographic North Pole"] --- MS["Magnetic South Pole"]
        GS["Geographic South Pole"] --- MN["Magnetic North Pole"]
        MS -->|"Field lines curve from magnetic N to magnetic S"| MN
    end

Exam Tip: This is confusing but important: the north pole of a compass points towards the Earth's geographic north. Since opposite poles attract, the Earth's magnetic south pole is near the geographic north pole. AQA has asked about this before — make sure you can explain it clearly.

The Compass

A compass contains a small bar magnet (the needle) that is free to rotate. The north pole of the compass needle points towards the Earth's magnetic south pole (which is near the geographic north pole).

When a compass is placed near a bar magnet, the compass needle aligns with the local magnetic field. The closer the compass is to the magnet, the more the needle is influenced by the bar magnet rather than the Earth's field.

Magnetic vs Non-Magnetic Materials — Required Knowledge

You must be able to distinguish between:

Magnetic materials — attracted to magnets (iron, steel, cobalt, nickel)
Magnetically hard materials — difficult to magnetise but retain their magnetism well (e.g., steel) — used for permanent magnets
Magnetically soft materials — easy to magnetise but lose their magnetism easily (e.g., iron) — used for electromagnets

Material Type	Easy to Magnetise?	Retains Magnetism?	Use
Magnetically hard (steel)	No (difficult)	Yes (retains well)	Permanent magnets
Magnetically soft (iron)	Yes (easy)	No (loses quickly)	Electromagnets, temporary magnets

Summary

Magnets have a north pole and a south pole; the field is strongest at the poles.
Like poles repel; unlike poles attract.
Permanent magnets produce their own magnetic field; induced magnets are only magnetic when in an external field and always attract.
A magnetic field is the region around a magnet where a force acts on magnetic materials or other magnets.
Field lines go from north to south, never cross, and are closer together where the field is stronger.
The Earth has a magnetic field; the magnetic south pole is near the geographic north pole.
Magnetically soft materials (iron) are used for electromagnets; magnetically hard materials (steel) are used for permanent magnets.

Exam Tip: You should be able to draw the field pattern around a bar magnet from memory. Practise sketching it — field lines should emerge from the north pole and curve around to enter the south pole. The lines should be smooth curves, and you must include arrows pointing from N to S.