Electric motirs

• Coil of wire in a magnetic field

  A coil of wire carrying a current in a magnetic field tends to rotate

  
• Why the coil in an magnetic field rotates

  Current in the one side of the coil causes a downward force, and current in the other side of the coil causes an upward force

  
• Electric motor


  A device that uses the motor effect to produce a turning effect in a coil of wire

  
• DC motor


  An electrical motor that uses direct current to produce a turning effect

  
• Direct current (dc)


  An electric current that flows in one direction only

  
• What happens when the coil is vertical in the magnetic field

  It moves parallel to the magnetic field lines and produces no force
• Reasons why the coil continues to rotate when it is vertical

  Due to the momentum of the motor and the split ring commutator
• Split-ring commutator


  Part of a dc motor that reverses the direction of the current every half turn

  
• Function of the connecting brushes

  Reconnect with the commutator after a half turn

  
• Why the connecting brushes are needed

  Allow the current to flow in the opposite direction through the wire in the coil so that each side of the coil is now near the opposite magnetic pole and the coil continues to rotate

  
• (higher-tier only)

  Headphones and loudspeakers

  Electrical devices that use the motor effect to produce sound

  
• (higher-tier only)

  How headphones and loudspeakers work

  Variations in an electric current cause variations in the magnetic field which causes a cone to move and create pressure variations in the air (sound waves)