Topic 12 - Magnetism

• Magnets

  Made of iron, cobalt, and nickel
• Magnetic poles


  • Like poles repel
  • Unlike poles attract
• Magnetic materials


  Can be magnetized permanently or made into temporary/induced magnets
• Making a needle magnetic


  1. Stroking a magnet past it

  2. Sticking it through a piece of cork
• Paper clips and a steel nail are not normally magnetic
• Magnet and magnetic material


  Magnetic material experiences a force in the magnetic field
• Induced magnetism


  Attaching a magnet to a nail concentrates the field lines, turning the nail into a temporary magnet
• Removing the magnet makes the nail no longer magnetic
• Stronger magnets like nickel or cobalt can pick up more paperclips
• Bar magnets


  • Have magnetic field lines associated with them
  • Field lines travel from north to south
  • Field lines do not cross
  • Closer together lines = greater field strength
• Showing magnetic field lines


  1. Cover a bar magnet with paper

  2. Sprinkle iron filings over the paper
• The Earth has a magnetic field that can be shown by a compass
• The Earth's north pole is actually a magnetic south pole
• Magnetic field around a current-carrying wire


  • Stronger nearest the wire
  • Stronger with greater current
• Determining direction of magnetic field around a wire

  Use right-hand or corkscrew rule
• Current in a wire


  Produces a magnetic field that interacts with a magnet, causing a "kicking wire effect"
• Fleming's left-hand rule


  Shows the relative directions of field, current, and resulting force
• Calculating magnetic field strength


  1. Use formula F = BIL

  2. Measure current, length, and force
• Solenoid


  Coil of wire that produces a strong, uniform magnetic field inside and weaker field outside
• Electric motor


  Uses the motor effect - forces on current-carrying wires in a magnetic field to cause rotation
• Electric motor operation


  Commutator allows continuous application of forces to rotate coil