Electromagnetism

• A current travelling along a wire produces a circular magnetic field around the wire.

  The magnetic field direction can be determined using the right hand grip rule.
• Motor

  • Current flows in the wire/coil.
  • This creates a magnetic field around the wire/coil.
  • This magnetic field interacts with the field from the permanent magnet.
  • This produces a force on the wire/coil which moves the wire/coil.
  • The split-ring commutator changes the direction of the current every half turn as it spins. This reverses the direction of the forces, allowing the coil to continue spinning.
• Loudspeaker

  • An alternating current from the source passes though the coils in the speaker.
  • This current is constantly changing direction and magnitude
  • This current creates a magnetic field around the coil
  • This field interacts with the magnetic field from the permanent magnets
  • Creating a constantly changing force on the coil.
  • This causes the coil to vibrate in and out as the direction of the force changes, moving the cone
  • The cone causes vibrations which we hear as sound waves.
• Fleming’s left hand rule.

  Thumb: force

  First finger: Magnetic Field

  Second finger: Current
• If you increase the magnitude of the current through a wire or the size of the magnet being used, you increase the force on the wire.

  If you change the direction of the current or reverse the poles of the magnet, you change the direction of the force on the wire