Permanent and Induced Magnetism

A magnet produces a magnetic field around itself. The field exerts forces on other magnets and on magnetic materials.

Magnetic materials

Only a few materials are magnetic (attracted to magnets): iron, steel (an alloy containing iron), nickel and cobalt. Non-magnetic materials (copper, aluminium, wood, plastic) are not attracted.

Permanent magnets and temporary magnets

A permanent magnet produces its own magnetic field all the time. It does not need an electric current. Examples: bar magnets, horseshoe magnets.

A temporary magnet (e.g. soft iron) is magnetic only while it is in a magnetic field or near another magnet. When the field is removed, it loses its magnetism quickly.

Steel retains magnetism well (hard magnetic material, used for permanent magnets). Iron magnetises and demagnetises easily (soft magnetic material, used for electromagnet cores and transformer cores).

Induced magnetism

When a magnetic material (e.g. iron) is placed in a magnetic field, it becomes a temporary magnet. The end closest to the north pole of the magnet becomes a south pole (opposite pole), which is why the material is attracted.

This explains why a magnet attracts an unmagnetised iron nail: the nail becomes temporarily magnetised with an induced south pole at the near end, and opposite poles attract.

Poles

Every magnet has a north pole and a south pole. Like poles repel; unlike poles attract.

Common errors and how to correct them

Saying aluminium or copper are magnetic. Only iron, steel, nickel and cobalt are magnetic. Aluminium and copper are not attracted to magnets.

Stating “a magnet attracts all metals.” Magnets only attract magnetic materials, not all metals. Gold, silver and copper are metals but are not magnetic.

How to apply this in an exam

When explaining attraction of an unmagnetised material, describe induced magnetism: the material becomes a temporary magnet with an opposite pole at the near end, and opposite poles attract.