Inductance

Inductance is a property of an electric circuit that opposes any change in the current flowing in that circuit. A magnetic field surrounds every electric current. According to a principle of physics known as Lenz's law, this magnetic field acts to oppose changes in the electric current. Inductance refers to the reaction of the circuit to this magnetic field opposition.

Inductance has no effect on a steady direct current because the magnetic field around the conductor carrying this current does not change. But if the current flow changes or alternates, the magnetic field also changes. This changing magnetic field induces (creates) a voltage in the conductor that opposes any additional increase or decrease in the flow of current.

Inductance that occurs in one circuit is called self-inductance, and inductance between two circuits is mutual inductance. If a wire carrying a current is wound into a coil, the inductance is increased. Such a coil is called an inductance coil or a choke coil. Its inductance can be further increased by inserting an iron core into the coil. Inductance is measured in units called henrys.

Electrical engineers use inductance coils to control electricity. For example, because inductance opposes the flow of alternating current, an inductance coil can serve as a filter to keep alternating current out of direct current circuits. Inductance coils are also used in tuning circuits in radio or television receivers.

Contributor: Lynn W. Hart, Ph.D., Physicist, Principal Staff, The Johns Hopkins Univ. Applied Physics Laboratory.

Inductance

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