Transformers

• what does AC in a coil create

  a changing magnetic field
• what happens next

  the changing magnetic field cuts through secondary coil, induces a current in the secondary coil - which is AC

  if the current was DC, magnetic field it produced would be constant, not inducing anything in the secondary coil
• more coils on secondary:

  step up transformer

  because voltage will be increased, changing field will cut through more of the secondary wire - larger PD
• fewer coils on the secondary

  step down transformer - smaller PD forms on secondary
• when does this work

  only with current if the transformer is 100% efficient, unless this is stated - assume not