Magnets (CIE IGCSE Physics: Co-ordinated Sciences (Double Award))

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 easily 

Temporary (induced) magnetism

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

Electromagnets

• An electromagnet can be made by winding coils of wire around a soft iron core

• An electromagnet can be switched on and off

  • When the current is flowing the electromagnet is switched on

  • When there is no current flowing then the electromagnet is switched off 

Electromagnet diagram

Differences between permanent and electromagnets

• There are many differences between permanent and electromagnets
  • These differences affect how these types of magnets are used
• Permanent magnets are always magnetic
  
  • They cannot be switched on and off
• Electromagnets are sometimes magnetic
  • An electromagnet is turned on by switching on the current passing through the coils of wire
  • The electromagnet is turned off by switching off the current
• It is not possible to change the strength of a permanent magnet
• The strength of an electromagnet can be changed in several ways:
  • By increasing the current
  • By increasing the number of turns of the coil
  • By adding a soft iron core