Magnets and Magnetic Fields

This lesson covers the fundamental properties of magnets and magnetic fields — as required by the Edexcel GCSE Physics specification (1PH0), Topic 8: Magnetism and Electromagnetism. You need to understand the behaviour of magnetic poles, identify magnetic materials, distinguish between permanent and induced magnets, and describe magnetic field patterns.

Magnetic Poles

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

The Law of Magnetism

Like poles repel — two north poles push apart; two south poles push apart.
Unlike poles attract — a north pole and a south pole pull together.

This is the fundamental rule of magnetism. It applies to all magnets regardless of size, shape or strength.

Exam Tip: The law of magnetism is analogous to electric charges: like repels like, unlike attracts. However, magnetic poles always come in pairs — you cannot have an isolated north or south pole. If you break a magnet in half, you get two smaller magnets, each with its own north and south pole.

Magnetic Materials

Only certain materials are attracted to magnets. These are called magnetic materials:

Material	Magnetic?	Notes
Iron	Yes	Soft magnetic material — easily magnetised and demagnetised
Steel	Yes	Hard magnetic material — retains magnetism (used for permanent magnets)
Nickel	Yes	Magnetic material
Cobalt	Yes	Magnetic material
Copper	No	Non-magnetic
Aluminium	No	Non-magnetic
Wood	No	Non-magnetic
Plastic	No	Non-magnetic

Key Points

Only iron, steel, nickel and cobalt are magnetic materials at GCSE level.
Non-magnetic materials are not repelled by magnets — they simply experience no force.
A magnetic material is attracted to both poles of a magnet (attraction does not tell you which pole is which).

Exam Tip: A common exam mistake is to say that all metals are magnetic. This is wrong — only iron, steel, nickel and cobalt are magnetic. Copper, aluminium, gold, silver and most other metals are not magnetic.

Permanent Magnets vs Induced Magnets

Permanent Magnets

A permanent magnet produces its own magnetic field. It does not need an external source of magnetism or electricity.

Key features:

Made from magnetically hard materials such as steel.
Always has a north and south pole.
Can attract or repel other magnets.
The magnetic field is always present — it cannot be switched off.

Induced Magnets (Temporary Magnets)

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

Key features:

Made from magnetically soft materials such as iron.
Only magnetic when inside an external magnetic field.
Always attracted to the permanent magnet (never repelled) — because the induced poles always align to create attraction.
The magnetism is temporary — it disappears when the inducing field is removed.

Comparing Permanent and Induced Magnets

Feature	Permanent Magnet	Induced Magnet
Material	Magnetically hard (e.g. steel)	Magnetically soft (e.g. iron)
Magnetism	Always present	Only while in a magnetic field
Can repel?	Yes (like poles)	No — always attracted
Switched off?	No	Yes (remove from field)

Exam Tip: If an exam question describes an object that is attracted to a magnet but you are not told it is a magnet itself, it could be a magnetic material experiencing induced magnetism. Induced magnets are always attracted, never repelled. The only way to prove something is a permanent magnet is to show repulsion — attraction alone is not enough.

Magnetic Fields

A magnetic field is the region around a magnet where a magnetic material (or another magnet) experiences a force.

Magnetic Field Lines

Magnetic field lines are used to represent a magnetic field. They show the direction and strength of the field:

Field lines go from north to south outside the magnet.
Inside the magnet, field lines go from south to north (forming continuous loops).
The closer together the field lines, the stronger the field.
The further apart the field lines, the weaker the field.
Field lines never cross.

Magnetic Field Patterns

graph TD
    A["Bar Magnet Field Pattern"] --> B["Field lines emerge from<br/>the NORTH pole"]
    B --> C["Field lines curve around<br/>through the surrounding space"]
    C --> D["Field lines enter at<br/>the SOUTH pole"]
    D --> E["Lines are closest together<br/>at the poles = strongest field"]
    E --> F["Lines spread further apart<br/>away from magnet = weaker field"]

    style A fill:#2c3e50,color:#fff
    style B fill:#c0392b,color:#fff
    style C fill:#e67e22,color:#fff
    style D fill:#2980b9,color:#fff
    style E fill:#27ae60,color:#fff
    style F fill:#8e44ad,color:#fff

Between Two Magnets

Arrangement	Field Pattern
Unlike poles facing (N–S)	Field lines run from N of one magnet to S of the other; attraction — uniform field between the poles
Like poles facing (N–N or S–S)	Field lines push away from each other; there is a neutral point between the magnets where the field is zero; repulsion

Plotting Magnetic Fields

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

Place a bar magnet on a piece of paper.
Place a small plotting compass near one pole of the magnet.
Mark the position of both ends of the compass needle.
Move the compass so that the tail of the needle is at the position where the head was.
Mark the new head position.
Repeat until you reach the other pole (or the edge of the paper).
Join the dots to form a smooth field line.
Add an arrow pointing from north to south.

Alternatively, you can sprinkle iron filings around a magnet to reveal the field pattern. The filings align with the field lines, but they do not show the direction (only the pattern).

Exam Tip: The Edexcel specification requires you to know how to investigate magnetic field patterns using a compass and iron filings. Be prepared to describe the method and interpret the results. Remember: iron filings show the shape of the field but NOT the direction — you need a compass for direction.

The Earth's Magnetic Field

The Earth has a magnetic field that behaves as though there is a giant bar magnet inside it:

The Earth's geographic North Pole is near a magnetic south pole — this is why the north-seeking pole of a compass points north (it is attracted to the Earth's magnetic south pole).
The Earth's magnetic field is relatively weak compared to most bar magnets.
It protects the Earth from charged particles in the solar wind.

Using a Compass

A compass contains a small bar magnet (the needle) that is free to rotate. The north-seeking pole of the compass aligns with the Earth's magnetic field, pointing towards the geographic North Pole.

Near a bar magnet, the compass needle is deflected — it points in the direction of the resultant magnetic field (the combination of the bar magnet's field and the Earth's field).
Far from any magnets, the compass points to geographic north.

Summary

Every magnet has a north and south pole — like poles repel, unlike poles attract.
Magnetic materials: iron, steel, nickel and cobalt.
Permanent magnets always have a magnetic field; induced magnets are temporary and only magnetic when in an external field.
A magnetic field is a region where a magnetic material experiences a force.
Field lines go from north to south outside the magnet; closer lines mean a stronger field.
Magnetic fields can be plotted using a compass (shows direction) or iron filings (shows pattern).
The Earth has a magnetic field — the geographic North Pole is near a magnetic south pole.
Repulsion is the only sure test that something is a permanent magnet.