Magnets and Magnetic Fields

This lesson covers permanent magnets, induced magnets, magnetic poles, the forces between them and how to map magnetic fields using field lines, as required by the Edexcel GCSE Combined Science specification (1SC0). A solid understanding of basic magnetism is essential before tackling electromagnets and the motor effect.

Magnetic Materials

Only a few materials are magnetic — they are attracted to magnets. The three magnetic elements you must know are:

Magnetic Element	Symbol
Iron	Fe
Cobalt	Co
Nickel	Ni

Steel (an alloy containing iron) is also magnetic.

Exam Tip: Copper, aluminium, gold and silver are not magnetic. A very common trick question asks whether all metals are magnetic — they are not.

Permanent and Induced Magnets

Feature	Permanent Magnet	Induced Magnet
Produces its own magnetic field?	Yes — at all times	Only when placed in a magnetic field
Keeps its magnetism?	Yes — indefinitely	No — loses it when removed from the field
Example	Bar magnet, horseshoe magnet	An iron nail attracted to a permanent magnet

How Induced Magnetism Works

When a magnetic material (e.g. a piece of iron) is placed inside a magnetic field, the magnetic domains inside the material line up with the external field. The material temporarily becomes a magnet itself. The end of the material nearest the magnet's north pole becomes a south pole (so it is attracted).

Magnetic Poles

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

The Law of Magnetism

Combination	Result
N — N	Repulsion
S — S	Repulsion
N — S	Attraction

Exam Tip: Repulsion is the only sure test for a magnet. Attraction could be caused by an induced magnet (e.g. an unmagnetised piece of iron will always be attracted to a magnet). Only two magnets can repel each other.

Magnetic Fields

A magnetic field is the region around a magnet where a magnetic force acts on another magnetic material or magnet. You cannot see a magnetic field, but you can represent it with field lines.

Properties of Magnetic Field Lines

Field lines go from north to south (outside the magnet).
The lines never cross.
Where the lines are closer together, the field is stronger.
Where the lines are further apart, the field is weaker.

graph LR
    subgraph "Bar Magnet Field Pattern"
    direction LR
    N["N pole"] -->|"Field lines curve outward"| S["S pole"]
    end

The field is strongest at the poles (lines are closest together) and weakest further from the magnet.

Plotting a Magnetic Field with a Compass

Method

Place a bar magnet on a sheet of paper and draw around it.
Place a plotting compass near the north pole of the magnet.
Mark the position of both ends of the compass needle with a dot.
Move the compass so that the tail of the needle sits on the dot just made for the head.
Mark the new position of the head with another dot.
Repeat until the trail of dots reaches the south pole (or runs off the paper).
Join the dots to form a smooth field line and add an arrow from N to S.
Repeat for several different starting positions around the magnet.

What the Compass Shows

The compass needle is itself a tiny magnet. Its north pole always points in the direction of the magnetic field — that is, away from the north pole of the bar magnet and towards the south pole.

Uniform and Non-Uniform Fields

Type	Description	Where Found
Uniform field	Field lines are parallel and equally spaced; field strength is the same everywhere	Between two flat, opposite magnetic poles
Non-uniform field	Field lines are curved and/or vary in spacing	Around a bar magnet

A uniform field exists between two flat, opposite poles placed close together (e.g. between the N and S faces of two bar magnets). The field lines are straight, parallel and evenly spaced.

The Earth's Magnetic Field

The Earth behaves as though it contains a giant bar magnet. The geographic North Pole is near a magnetic south pole (which is why the north-seeking pole of a compass points towards geographic north).

Feature	Detail
Shape	Similar to a bar magnet field
Cause	Convection currents in the molten iron outer core
Use	Allows navigation with a compass

Worked Example

A student places two bar magnets end to end on a table, with a north pole facing a south pole. Describe the field pattern between the magnets.

The field lines run in straight, parallel lines from the north pole of one magnet to the south pole of the other. The lines are equally spaced (approximately), showing the field between the poles is roughly uniform.

Common Misconceptions

Misconception	Correction
All metals are magnetic	Only iron, cobalt, nickel (and their alloys) are magnetic
Attraction proves an object is a magnet	Attraction could be induced magnetism; only repulsion proves both objects are magnets
Field lines start at south and end at north	Field lines go from north to south (outside the magnet)
A compass needle points to a magnetic north pole	A compass north-seeking pole is attracted to the Earth's magnetic south pole, which is near the geographic North Pole

Summary

Magnetic materials: iron, cobalt, nickel (and alloys like steel).
Permanent magnets produce their own field; induced magnets are temporary.
Like poles repel; unlike poles attract. Repulsion is the only sure test for a magnet.
Magnetic field lines go from north to south, never cross, and are closer together where the field is stronger.
A plotting compass can be used to trace field lines around a bar magnet.
A uniform field has parallel, equally spaced field lines (found between two opposite flat poles).
The Earth has a magnetic field similar to a bar magnet, enabling compass navigation.