Induced and permanent magnetism

Iron, steel, nickel and cobalt are magnetic materials. They are affected by magnets and are attracted to either pole of a magnet.

Permanent magnets

A permanent magnet is often made from a magnetic material such as iron. A permanent magnet always causes a force on other magnets, or on magnetic materials. Key features of a permanent magnet:

  • it produces its own magnetic field
  • the magnetic field cannot be turned on and off - it is there all the time

Bar magnets and horseshoe magnets are examples of permanent magnets.

Induced magnets

Iron filings are attracted to a bar magnet.
Iron filings are attracted to a bar magnet

Unlike a permanent magnet, an induced magnet only becomes a magnet when it is placed in a magnetic field. The induced magnetism is quickly lost when the magnet is removed from the magnetic field.

The iron filings in the image become induced magnets when they are near the bar magnet. Like all induced magnets:

  • they are only attracted by other magnets, they are not repelled
  • they lose most or all of their magnetism when they are removed from the magnetic field

Testing for magnetism

A permanent magnet can:

  • attract or repel another permanent magnet
  • attract a magnetic material (but not repel it)

This means that you can only show that an object is a permanent magnet by checking if it repels another magnet.