Electromagnetism

• Electromagnet


  A magnet formed by an electrical current. An electromagnet can be switched on and off.
• How an electromagnet works

  1. Electrical current flows through copper wire

  2. Creates a magnetic field

  3. Adding an iron core makes the magnetic field stronger
• Electromagnet


  • Coiling the wire more times around the iron core builds up the magnetic field and makes the electromagnet stronger
  • Electromagnets can be switched on and off - they are only magnets while current is flowing through the coil
  • Electromagnets can be made stronger or weaker
• When the power is on


  The electromagnet attracts magnetic metals
• When the power is off

  The magnetic field disappears and the metals drop
• Ways to increase the strength of an electromagnet

  • Using more turns on the coil of wire
  • Increasing the current through the wire
  • Adding a soft iron core
• Motor effect


  The force on a current-carrying wire near a permanent magnet causes the wire to move
• The motor effect is used in DC motors
• Loudspeakers


  Use the motor effect - a coil of wire attached to a cone is pushed and pulled by a magnetic field, causing the cone to vibrate and produce sound
• Microphones


  Use the generator effect - incoming sound causes a coil of wire to move near a magnet, generating an electrical output