transformers

• transformers change the size of the potential difference of an alternating current
• two coils or transformers

  primary and secondary coil joined with an iron core
• when an alternating p.d. is applied across the primary coil , it produces an alternating magnetic field
• as iron is a magnetic material , the core also becomes magnetised because the coil is producing an alternating magnetic field the magnetisation in the core also alternates a changing magnetic field induces a p.d. in the secondary coil
• power of a primary coil equation

  power = p.d. x current
• power equation

  power in primary coil = power in secondary coil if the secondary coil has more turns , the p.d. increases and the current decreases
• step-down transformers

  • step the voltage down
  • they have more turns on the primary coil than the secondary coil
• step-up transformers

  • step the voltage up
  • more turns on the secondary coil than the primary coil
• the transformer equation

  p.d. across primary coil number of turns

  (V) in primary coil

  —————————————— = —————————

  p.d. across secondary coil number of turns

  (V) in secondary coil
• a step-down transformer has a primary coil with 22000 turns and an input voltage of 1.6 V . The output voltage is 0.4 V . Calculate the number of turns on the secondary coil.

  5500 turns
• alternating current and the x axis


  always crosses the x axis
• direct current and the x axis


  never crosses the x axis
• transformer 


  a loop of iron with two coils that can be used to increase or decrease a potential difference