Magnetism and Electromagnetism

• inside a compass is a tiny bar magnet- the north pole of this magnet is attracted to the south pole of any nearby magnet (to the compass points in the direction of the magnetic field it's in)
• permanent magnets= produce their own magnetic field

  induced magnets= are magnetic materials that turn into a magnet when they're put into a magnetic field

  the force between permanent and induced magnets are always attractive
• when a current flows through a wire, a magnetic field is created around the wire

  the field is made up of concentric circles perpendicular to the wire, with the wire in the centre
• Fleming's left hand rule:

  thumb = movement

  index = magnetic field

  middle = current
• you can increase the strength of a magnetic field that a wire produces by wrapping the wire into a coil called a solenoid (this happens because the field lines around each loop of wire line up with each other) --> this results in lots of field lines pointing in the same direction

  
  

  the magnetic field inside a solenoid is strong and uniform (has the same strength and direction at every point in that region)
• you can increase the field strength of the solenoid even more by putting a block of iron in the centre (as the iron core becomes an induced magnet whenever the current is flowing)
• bar magnets = changes direction and it goes in and out
• the generator effect creates a p.d. in a conductor, and a current if the conductor is a part of a complete circuit

  this can be done by moving a magnet in a coil of wire or moving a conductor in a magnetic field
• alternators generate alternating current --> alternators rotate a coil in a magnetic field, their construction is pretty much like a motor

  as the coil spins, a current is induced- the current changes direction at every half term

  this produces an alternating potential difference