Magnetism

• Magnets have two poles (do not confuse this when positive and negative whihc is used to describe charges rather than poles)

  • north pole
  • south pole
• Law of magnetism:

  • like poles repel
  • unlike poles attract
  • magnetic materials (NOT MAGNETS!!!) can attract either pole
• Law of magnetism

  A) attract

  B) repel

  C) attracted to either pole

  
• There’s a neutral point in the blank area between two alike poles

  
• Electricity & magnetism are two aspects of the same thing

  • magnetic fields are electric fields when an electrically charged object starts moving
  • an electron current can create magnetism
• When two magnets are held together there is a force between that is either pushing or attracting them together

  • the closer the pole, the greater the force between
• Magnets produce magnetic fields

  • magnetic field - the area around a magnet where another magnet or magnetic material will experience a non-contact force
• Only a magnet can repel another magnet

  • the force between a magnetic material and a magnet is always attractive, no matter the pole
• Magnetism is a non-contact force as objects don’t need to touch eachother to feel that force
• The electrons in a material itself can be considered as tiny magnets and can help identify whether a material is magnetic or not

  • if all the poles of the tiny magnets align, then the substance is magnetic
  • if all the poles of the tiny magnets do not align, then the substance isn’t magnetic as the magnetic fields cancel each other out
• Tiny magnets:

  A) magnetic material

  B) non-magnetic material

  
• Magnetic material becomes magnetised when under the influence of a magnetic field (induced by the magnet) and all the tiny magnets shift to match with the corresponding pole e.g. south pole of tiny magnets in the magnetic material shifts to match with the permanent magnet’s north pole

  • magnetic materials go back to their unmagnetized state when the permanent magnet is removed

  
• Magnetic materials

  • always experience an attractive force when placed in a magnetic field
  • still attracted to a magnet when unmagnetised
  • can be magnetised to form a magnet
• Non-magnetic materials

  • don’t experience a force when placed in a magnetic field
• Permanent magnets are usually made out of steel as they tend to stay magnetised
• Uses of permanent magnets:

  • compasses
  • school lab experiments
  • toys
  • fridge magnets
• • Electromagnets - using electricity to create a magnet from a current-carrying wire
  • magnetism can be switched on and off
  • soft iron is the metal normally used for electromagnets as it can easily become a temporary magnet
• Uses of electromagnets:

  • MRI scanners
  • speakers and earphones
  • recycling
  • mag-lev trains
• How do you test if a material is magnetised using a bar magnet

  If one end of the material is attracted to one end of the bar magnet and the other end of the material is repelled to another end of the bar magnet