What is a magnet?
A magnet is an object that produces a magnetic field — an invisible region of force that can attract certain materials (iron, nickel, cobalt and steel) and interact with other magnets. Magnetism is one of the fundamental forces of nature, closely related to electricity.
Magnetic materials are called ferromagnetic materials. Iron, nickel, and cobalt are the most common. Materials like wood, plastic, and aluminium are non-magnetic and are not attracted to magnets.
Magnetic poles
Every magnet has two poles — a North (N) pole and a South (S) pole. The magnetic force is strongest at the poles. The key rule governing poles is:
Like poles REPEL · Unlike poles ATTRACT
- Two North poles pushed together — they repel (push away from each other).
- Two South poles pushed together — they repel.
- A North pole and a South pole — they attract (pull towards each other).
You CANNOT isolate a single magnetic pole. If you cut a bar magnet in half, each half becomes a complete magnet with its own N and S pole.
Magnetic field lines
A magnetic field is the region around a magnet where a magnetic force can be detected. We represent it using field lines (also called lines of flux):
- Field lines travel from the North pole to the South pole outside the magnet.
- Inside the magnet, field lines travel from South to North (forming closed loops).
- Where field lines are close together, the field is strong.
- Where field lines are spread apart, the field is weak.
- Field lines never cross each other.
Permanent vs temporary magnets
| Type | Description | Example |
|---|
| Permanent magnet | Retains its magnetism indefinitely under normal conditions. | Bar magnet, fridge magnet, horseshoe magnet |
| Temporary magnet | Only magnetic while in the presence of another magnet or magnetic field. | Iron nail held next to a magnet, iron filings |
| Electromagnet | Produced by electric current flowing through a coil of wire. Can be switched on and off. | Electric motors, MRI machines, scrapyard cranes |
Earth as a magnet
The Earth behaves like a giant bar magnet. Its core (made largely of liquid iron and nickel) generates a magnetic field that extends far into space, forming the magnetosphere. This protects life on Earth from harmful solar wind particles.
- Earth's geographic North Pole is actually near a magnetic South Pole — that is why the North-seeking end of a compass needle (the N pole) is attracted to it.
- The angle between geographic north and magnetic north is called magnetic declination.
- A compass is a freely suspended magnetic needle that aligns with Earth's magnetic field, always pointing approximately north.
Electromagnetism: In 1820, Hans Christian Ørsted discovered that an electric current creates a magnetic field around it. This connection between electricity and magnetism — called electromagnetism — is the basis of electric motors, generators, transformers, and MRI machines.
Applications of magnetism
- Compass: Uses Earth's magnetic field for navigation.
- Electric motor: Uses the force between a current-carrying coil and a magnet to produce rotation.
- Generator: Converts kinetic energy to electrical energy using electromagnetic induction.
- Maglev trains: Use powerful electromagnets to levitate and propel trains without friction.
- MRI (Magnetic Resonance Imaging): Uses very strong magnetic fields to image the inside of the human body.
- Loudspeakers: Use an electromagnet vibrating near a permanent magnet to produce sound.