speakers and microphones

• microphones

  a device that converts sound waves into electrical signals - use generator effect to induce a changing current from the pressure variations of sound waves
• headphones

  contain small loudspeakers - use reverse effect to microphones - motor effect variations in an electric current cause variations in an electric field produced by an electromagnet which causes a cone to move , which creates pressure variations in the air and form sound waves
• describe how a speaker produces sound

  • current in the coil creates a magnetic field
  • the magnetic field interacts with the permanent magnets generating a force which pushes the cone outwards
  • the current is made to flow in the opposite direction
  • direction of magnetic field reverses
  • force on cone now pulls it back in
  • this repeatedly alters the current direction which makes the cone vibrate in and out
  • the cone vibrations vide pressure in the air - sound waves
• describe how a moving coil microphone works

  • pressure variations in sound waves cause the flexible diaphragm to vibrate
  • vibrarions in diaphragm causes vibrations in coil
  • coil moves in relation to a permanent magnet so a potential difference is induced in the coil
• the coil is part of a complete circuit so the induced potential difference causes a current to flow around the circuit

  the changing size and direction of induced current matches the vibrations of the coil

  the electrical signals generated match the pressure variations in the sound waves