A potential difference is induced current carrying wire if the wire is moved inside a magnetic field (not parallel to) or a magnetic field changes near the current carrying wire. The strength of the induced potential difference depends on two things the speed at which the magnetic field changes or the current carrying wire is moved and the strength of the magnetic field.
The basic principle here is that the charges (current carrying wire) ‘cut’ through the field lines. So if you were to rotate a magnet inside a solenoid then intuitively you would induce a potential difference.

You must be able to recall the layout of a transformer. There are several important things you must remember about Transformers:-
  • The potential difference must be alternating.
  • In order to be able to change the output voltage there must be the difference in the number of turns between the primary and secondary solenoid.
  • A transformer changes the magnitude of the voltage.

Because P = VI and also considering that a moving charge causes friction (and therefore heat loss) in a wire, it seems sensible to make V as large as possible. For this, the National Grid uses step up and step-down transformers. The power loss is greatly reduced while still being able to make the potential difference safe for use in homes when it gets there.

Remember:-

primary voltage ÷ secondary voltage = no. turns the primary coil ÷ no. turns in the secondary coil

Vp ÷ Vs = np ÷ ns

You also need to recall:-

input power = output power

VpIp = VsIs

When the transformer is 100% efficient