Electromagnetic induction can create a voltage by movement of a conductor in a magnetic field. This voltage can make current flow. Transformers use electromagnetic induction to change the voltage of alternating currents.
A basic transformer is made from two coils of wire, a primary coil from the alternating current (ac) input and a secondary coil leading to the ac output. The coils are not electrically connected. Instead, they are wound around an iron core. This is easily magnetised and can carry magnetic fields from the primary coil to the secondary coil.