Glossary term
Inductance
The property of an electrical conductor or circuit by which changing current produces magnetic flux and induced voltage.
Definition
quantityInductance is the property of a circuit or conductor that relates changing current to magnetic flux linkage and induced voltage.
A current flowing through a conductor creates a magnetic field. When current changes, the magnetic field changes and induces a voltage opposing that change. Inductance quantifies this effect. It is central to motors, transformers, inductors, relays, solenoids, transmission lines, switching converters, filters, and electromagnetic compatibility.
Inductance links electrical current to magnetic field energy. When current flows, magnetic flux is produced around the conductor or through a magnetic core. If the current changes, the changing flux induces a voltage that opposes the change:
where L is inductance. The unit is the henry. One henry produces one volt when current changes at one ampere per second.
Inductance can also be understood through flux linkage:
where \lambda is flux linkage. For a coil, flux linkage depends on number of turns, geometry, magnetic permeability, air gaps, and core saturation.
Energy storage and impedance
An inductor stores energy in a magnetic field:
This stored energy must go somewhere when current is interrupted. That is why relay coils, motors, solenoids, and switching converters require flyback paths, clamps, snubbers, or controlled switching. Opening an inductive circuit abruptly can produce high voltage transients.
In sinusoidal AC analysis, ideal inductive impedance is:
Inductive reactance increases with frequency, so inductors tend to oppose rapid current changes. This makes them useful in filters, energy storage, current smoothing, and electromagnetic interference control.
Self and mutual inductance
Self-inductance describes voltage induced in a circuit by its own changing current. Mutual inductance describes voltage induced in one circuit by changing current in another. Transformers, coupled inductors, wireless power systems, and many noise-coupling problems rely on mutual inductance.
Parasitic inductance appears in every conductor, trace, lead, package, and cable. At high switching speeds, even small parasitic inductance can create voltage overshoot, ringing, ground bounce, electromagnetic emissions, and device stress. Layout is therefore part of inductance design.
Common mistakes
A common mistake is treating inductance as ideal and constant. Real inductors have winding resistance, core loss, parasitic capacitance, saturation, temperature effects, frequency-dependent losses, and current ratings. Another mistake is ignoring current path geometry. Loop area often controls unwanted inductance more than conductor length alone. Good design states the operating current, frequency range, saturation current, core material, winding resistance, thermal limit, and measurement condition.