Inductance is a property of an electric circuit that opposes any change in the current flowing in that circuit. Every electric current creates—and is surrounded by—a magnetic field. A magnetic field is the influence that a magnet—in this case, the flowing current—creates in the region around it. If the current in the circuit changes, so does the magnetic field. The changing magnetic field, in turn, produces an electric field, which creates an electromotive force, also called voltage. The force always “pushes” against the change in current. The unit of measure for inductance is called the henry (H) to honor the American physicist Joseph Henry.
Inductance in a circuit is called self-inductance if it is caused only by its own changing magnetic field. But magnetic fields from other circuits nearby can also cause inductance in a circuit, called mutual inductance.
If a wire carrying a current is wound into a coil, the magnetic field is strengthened inside the coil. Stronger magnetic fields produce more electromotive force. Thus, the coil increases inductance. Such a coil is called an inductor or inductance coil. Inserting an iron core into the coil further concentrates and strengthens the magnetic field and thus the resulting inductance.
Engineers and scientists use inductors to control the flow of current in circuits. For example, inductance opposes alternating current (AC), current that regularly reverses its direction of flow, in circuits. But inductance has no effect on direct current (DC), which does not alternate. Thus, inductors can serve as filters to keep alternating current out of direct current circuits. Inductors are also used in tuning radio and television receivers and in many other electric devices.
