Transformers

• Transformers


  Change the size of a potential difference (pd). They will only work with alternating current
• How transformers work


  1. Alternating pd applied across primary coil

  2. Iron core magnetises and demagnetises quickly

  3. Changing magnetic field induces alternating pd in secondary coil

  4. If secondary coil is in a complete circuit, current is induced
• Ratio between primary and secondary potential differences


  Same as the ratio between the number of turns on the primary and secondary coils
• Step-up transformers


  • Have more turns on the secondary coil than the primary coil
  • Step the potential difference up (increase it)
• Step-down transformers


  • Have more turns on the primary coil than the secondary
  • Step the potential difference down (decrease it)
• Transformers are almost 100% efficient
• For a given power

  A high pd is needed for a low current to reduce energy wasted heating wires and surroundings
• The transformer equation can be used to work out the number of turns needed to increase the pd (and decrease the current) to the right levels for power transmission in the national grid