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induction coil[in′dək·shən ‚kȯil]
A device for producing a high-voltage alternating current or high-voltage pulses from a low-voltage direct current. The largest modern use of the induction coil is in the ignition system of internal combustion engines, such as automobile engines. Devices of similar construction, known as vibrators, are used as rectifiers and synchronous inverters. See Ignition system
The illustration shows a typical circuit diagram for an induction coil. The primary coil, wound on the iron core, consists of only a few turns. The secondary coil, wound over the primary, consists of a large number of turns.
Induction coils of a different type are used in telephone circuits to step up the voltage from the transmitter and match the impedance of the line. The direct current in the circuit varies in magnitude at speech frequencies; therefore, no interrupter contacts are necessary. Still another type of induction coil, called a reactor, is really a one-winding transformer designed to produce a definite voltage drop for a given current. See Reactor (electricity)
inductorA coil of wire that generates a magnetic field when current is passed through it. The strength of the magnetic field is measured in henrys (H). When the current is removed, as the magnetic field disintegrates, it "induces" a brief current in the opposite direction of the original. Thus "electromagnetic induction" is caused by the opening and closing of a DC circuit or the continuous changing of directions in an AC circuit.
An induction coil impedes the flow of high-frequencies in an AC circuit, which is why inductors are used as surge protectors, choking off any high-frequency shifts. The tiny donuts placed on the end of signal cables and the load coils placed into telephone networks are examples. See electromagnetic induction.