magnets

• magnetic forces are strongest at the poles of the magnet
• when 2 magnets are brought close together they exert a force on each other:

  • 2 like poles repel
  • 2 unlike poles attract
• attraction and repulsion are examples of non-contact force
• a permanent magnet produces its own magnetic field
• if we bring a permanent magnet close to another permanent magnet, they can attract or repel
• an induced magnetic is a material that becomes a magnet when it is placed in a magnetic field

  = always the causes the force of attraction
• when an induced magnet is removed from the magnetic field it loses most / all of its magnetism quickly
• a magnetic field is the region around a magnet where a force acts on another magnet or on a magnetic material (iron/steel/cobalt/nickel)
• magnetic materials:

  • iron
  • steel
  • cobalt
  • nickel
• the force between a magnet and a magnetic material is always one of attraction
• the strength of the magnetic field depends on the distance from the magnet

  --> field is strongest at the poles (so closest field lines)
• finding direction of magnetic field:

  • compass, which contains a small bar magnet
  • first, place compass near North Pole of bar magnet and cross of North Pole of compass
  • move compass, so South Pole of compass is on cross, and draw another cross at North Pole of compass
  • continue until plotted a complete magnetic field line
  • connect all the dots with a line and show direction (N to S) with arrow
  • repeat starting at different points around North Pole of bar magnet
• the direction of a magnetic field at any point is given by the direction of the force that would act on another North Pole placed at that point

  the direction of a magnetic field line is from north to south
• where the magnetic field lines are closer together shows where the field is the strongest

  = poles
• evidence that the core of the earth must be magnetic:

  • a magnetic compass contains a small bar magnet
  • if we hold the compass, away from any magnets, then the needle always points NORTH to SOUTH
  • = earth has its own magnetic field
  • due to the earths core