In it's simplest form it consist of, two inductive coils which are electrically separated but magnetically linked through a path of low reluctance. If one coil (primary) is connected to source of alternating voltage, an alternating flux is set up in the laminated core, most of which is linked with the other coil in which it produces mutually-induced e.m.f. (according to Faraday's Laws of Electromagnetic Induction. If the second coil (secondary) circuit is closed, a current flows in it and so electric energy is transferred (entirely magnetically) from the first coil to the second coil.