motors and loudspeakers

• in a simple d.c ( direct current ) motor , a current-carrying coil sits between two opposite poles of a magnet
• simple electric motor


  because the current is flowing in different directions on each side of the coil , and each side of the coil is perpendicular to the magnetic field , each side will experience forces in opposite directions because the coil is on a spindle and the forces act in opposite directions on each side , it rotates
• the split ring commutator swaps the connections from one end of the coil to the other as it turns, so that the force always acts in the same direction.
• simple electric motor

  the direction of the motor can be reversed either by reversing the current or reversing the magnetic field
• simple electric motor

  to speed up the motor , increase the current , add more turns to the coil or increase the magnetic flux density
• how to figure out how a coil is rotating using flemings left hand rule:

  1. draw arrows to show the direction of the magnetic field lines and the current
  2. use the LHR on one side of the coil
  3. draw in the direction of the force ( motion ) for this side of the coil
• loudspeaker


  contains a coil of wire which is surrounded by one magnet and a magnet inside the coil
• how a loudspeaker works

  a.c. electrical signals are fed to the coil of wire which is wrapped around the base of the cone . The interaction between the magnetic field and the current in the coil forces the coil to move in one direction . The current changes direction forcing the coil back in the other direction . As the current continues to alternate , the coil moves back and forth . These movements make the cone vibrate . This creates pressure variations in the air ( e.g. sound )
• state three properties that could be changed to decrease the speed of an electric motor.

  decrease current / decrease number of turns on the coil / decrease the magnetic flux density