Induction Coil

—An induction coil is e entially a transformer with open magnetic circuit in which a pulsating direct current in the primary induces an alternating current of high voltage in the secondary. The primary usually consists of comparatively heavy insulated copper wire wound upon a core of annealed iron wire, and the secondary of fine wire is wound over the primary. _ Induction coils are used in X-ray work, wirele telegraphy, electrotherapy, internal combustion motor ignition, etc. Sometimes termed a spark coil.