Easy one:
1) To step up the voltage using a transformer, the number of coils of the secondary coil wrapped around the iron core must be GREATER than the number of coils of the primary coil. Because the primary coil will supply AC current (changing magnetic flux) will have a relative motion with the secondary coil and induce an AC current in the secondary coil. The amount of magnetic flux threading the secondary coil is greater, as there are more turns, and Faraday's Law states that "induced emf = to the rate at which magnetic flux is changing with time"
2) To step down the voltage, oppositely, the number of coils of the secondary coil must be less than the number of Coils of the primary coil.
http://scienceaid.co.uk/physics/electricity/images/transformer.png
Can use the Vp / Vs = np / ns
V = emf or voltage
n = number of loops, turns, what ever
