induction coil

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A transformer, often used in automotive ignition systems, in which an interrupted, low-voltage direct current in the primary is converted into an intermittent, high-voltage current in the secondary.

from The Century Dictionary.

• noun In electricity, an apparatus for producing currents by induction, and for utilizing them. It consists essentially of two coils wound on a hollow cylinder, within which is a core formed of a bar of soft iron or a bundle of soft iron wires. One of the coils (see induction, 6), called the primary coil, of comparatively coarse wire, is connected with the battery by means of an arrangement for making and breaking connection with it, so as to produce temporary currents; the other, the secondary coil, of very fine wire, is wound round the first, but carefully insulated from it, and in it is generated a current by induction every time the current begins or stops in the primary coil. The currents produced by the induction-coil may have a very high electromotive force and hence great power of overcoming resistance. With a very large induction-coil, in the construction of the secondary coil of which nearly 300 miles of wire were used, sparks over 40 inches in length have been obtained. The induction-coil is often called the Ruhmkorff coil, or inductorium. See transformer.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun a transformer that produces a high voltage alternating current pulse from a low voltage direct current supply, especially such a device in the starter motor of an automobile

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a coil for producing a high voltage from a low-voltage source