4.2.8 generators

• • Alternating current (AC) is generated by a rotating-coil generator, where a coil of wire is rotated inside a fixed magnetic field.
  • When the coil rotates, it cuts across the magnetic field lines on the diagram above and a p.d is induced.
  • The induced p.d causes a current to flow in the coil of wire.
  • The faster the coil cuts across lines, the greater the magnitude (size) of the induced p.d.

  
• In a dynamo, a coil of wire rotates and the magnet is fixed.

  • coil rotates, generates a p.d. in one direction.
  • split-ring commutator reverses the direction of the current every half-turn of the coil. makes sure that current is always moving in the same direction to keep the coil rotating.
  • potential difference is largest when coil and the magnetic field are parallel.
  • When the coil ‘cuts’ across the magnetic field at the fastest rate.
  • potential difference is zero when coil is perpendicular (at right angles) to the magnetic field.
  • When the coil does not ‘cut’ the field lines at all.

  
• The potential difference is largest when the coil and the magnetic field are in parallel.
• Induced Potential Varies With Time in a Dynamo

  
• Features of a rotating-coil generator

  • a rotating coil of wire
  • a fixed magnetic field
• A microphone uses the generator effect in the opposite way to a speaker.

  • The sound waves that hit the microphone make a coil inside a magnet vibrate.
  • The coil vibrates at the same frequency as the sound wave coming in.
  • This induces a potential difference and current in the coil.

  
• What does a microphone convert into electrical energy?

  Sound waves
• The coil of wire in a microphone vibrates at the same frequency as the sound wave coming in.
• Microphone

  • the sound waves that hit the microphone make a coil inside a magnet vibrate
  • the coil vibrates at the same frequency as the sound wave coming in
  • this induces a potential difference and current in the coil