What is the difference between permanent and temporary magnets?

Permanent magnets retain their magnetic properties for a long time, while temporary magnets only exhibit magnetism under certain conditions.

Permanent magnets are made from materials, often metals, that are inherently magnetic. These materials, such as iron, nickel, and cobalt, have a structure that allows them to retain their magnetic properties over a long period of time, even when they are not in a magnetic field. This is due to the alignment of their magnetic domains, which are small, magnetically aligned areas within the material. When these domains are aligned in the same direction, the material becomes magnetised. This alignment is usually achieved through a process called magnetisation, which involves exposing the material to a strong magnetic field. Once magnetised, a permanent magnet will retain its magnetism indefinitely, unless it is demagnetised by heat, hammering or other forces.

Temporary magnets, on the other hand, are not inherently magnetic but can become magnetised when exposed to a magnetic field. These materials, such as soft iron, have a structure that allows their magnetic domains to align in the presence of a magnetic field, but this alignment is temporary. Once the magnetic field is removed, the domains return to their original, random orientations, and the material loses its magnetism. This makes temporary magnets useful in applications where magnetism needs to be switched on and off, such as in electric motors or generators.

In summary, the main difference between permanent and temporary magnets lies in their ability to retain magnetism. Permanent magnets maintain their magnetic properties for a long time, while temporary magnets only exhibit magnetism when in a magnetic field and lose it once the field is removed.