Induction Coil

Induction coil is an electrical transformer that produces high-voltage alternating current from lower voltage current. An induction coil has two windings of wire--a primary winding and a secondary winding that has more turns of wire than the primary one. If the current flowing in the primary winding is interrupted repeatedly, it creates a changing magnetic field around both windings. This changing field causes an electric current to flow in the secondary winding because of electromagnetic induction (see Electromagnetism). The voltage in this winding is much higher than that in the primary winding. This is because there are more turns of wire in the secondary winding for the field to act on.

From The World Book^™ Multimedia Encyclopedia ©1998 World Book, Inc., 525 W. Monroe, Chicago, IL 60661. All rights reserved.
World Book diagram.

The way the current supplied to the primary winding is interrupted depends on the type of coil. In induction coils used to fire the spark plugs in some automobile engines, for example, the primary current is interrupted by mechanical breaker points that are opened and closed by the car's distributor. In induction coils used to ignite gas stoves, jet engines, and oil burners, the primary current is broken by a magnetic vibrator similar to the type used in doorbells. Some induction coils use a transistorized electronic circuit to interrupt the primary current.

Contributor: Douglas M. Lapp, Ed.D., Director, National Science Resources Center, National Academy of Sciences/Smithsonian Institution.

Induction Coil

Master Index