The term induction coil, in current usage, usually refers to a passive electrical device used to produce high voltage pulses from a low voltage DC supply. It consists of two coils of copper wire wound around an iron core. One coil is made of coarse wire, the other of many turns of fine wire. Electrical current is passed through the first coil, which creates a magnetic field, storing energy. When the current is interrupted the magnetic field collapses, releasing the energy from the second coil as a high voltage spike.

The induction coil was discovered in early experiments with electricity, probably by Nicholas Callan in 1836, and well developed by Heinrich Ruhmkorff . It remains in common use as the ignition coil or spark coil in ignition system of internal combustion engines. A small version is used to trigger the flash tube in cameras.

The term is also used for a coil carrying high-frequency AC current and intended to induce some effect such as in induction heating or zone melting.

Induction Coil was also the title of William Stanley’s patent of 1885 which was however the prototype of the modern transformer.