Magnets (Cambridge (CIE) IGCSE Physics): Revision Note

Induced magnetism

Magnetic materials

• Very few metals in the periodic table are magnetic

• The magnetic metals are:

  • iron

  • cobalt

  • nickel

  • steel is an alloy which contains iron, so it is also magnetic

• Magnetic materials (which are not magnets) will always be attracted to the magnet, regardless of which pole is held close to it

• Bringing a material close to a known magnet will determine if the material is magnetic, non-magnetic or if it is a magnet itself

  • It is a magnet if it is repelled by the known magnet

  • It is a magnetic material if it is attracted to the known magnet

  • It is a non-magnetic material if it is neither attracted nor repelled by the known magnet

Types of magnets

• There are two types of magnets:

  • permanent magnets

  • induced (also called temporary) magnets

Permanent magnets

• Permanent magnets are made out of permanent magnetic materials, for example, steel

• A permanent magnet will produce its own magnetic field

  • It will not lose its magnetism

Temporary (induced) magnets

• An induced magnet is a material with a soft iron core that becomes a magnet temporarily when it is placed in a magnetic field

  • Induced magnetism always causes a force of attraction between the permanent magnet creating the magnetic field and the induced magnet 

  • When this happens it is said that the material has been magnetised

  • This means that the end of the material closest to the magnet will have the opposite pole to that of the magnet pole closest to the material

• When removed from the magnetic field, the material will lose its induced magnetism quickly and become unmagnetised

  • Some objects such as paperclips or needles (made from steel) can be magnetised and will remain magnetic for a while

  • Other objects, such as electromagnets or transformers (which are made from soft iron) will be unmagnetised (no longer magnetised) as soon as the cause of the induced magnetism is removed