The transformer — Explain

Explain the principle of operation of a simple iron-cored transformer.

An alternating current in the primary coil produces a changing (alternating) magnetic field in the soft-iron core. This changing field links with the secondary coil and, by electromagnetic induction, induces an alternating e.m.f. across it (producing a current if the secondary circuit is complete). A transformer only works with a.c., since a steady d.c. current would produce a constant field with no change to induce an e.m.f.