Inductor

An inductor, also called a coil, is a passive two-terminal electrical component which resists or opposes any changes in electric current passing through it. It consists of a conductor such as a wire, usually wound into a coil. When a current flows through it, energy is stored temporarily in a magnetic field in the coil. When the current flowing through an inductor changes, the time-varying magnetic field induces a voltage in the conductor, according to Faraday’s law of electromagnetic induction, which opposes the change in current that created it.

Inductor Symbol

Inductor Circuit

The current, i that flows through an inductor produces a magnetic flux that is proportional to it. But unlike a Capacitor which oppose a change of voltage across their plates, an inductor opposes the rate of change of current flowing through it due to the build up of self-induced energy within its magnetic field.

In other words, inductors resist or oppose changes of current but will easily pass a steady state DC current. This ability of an inductor to resist changes in current and which also relates current, i with its magnetic flux linkage, NΦ as a constant of proportionality is called Inductance which is given the symbol L with units of Henry, (H) after Joseph Henry.

L = NΦ / I

where, N = number of turns in coil

          Φ = flux in weber

           I = current in ampere

Because the Henry is a relatively large unit of inductance in its own right, for the smaller inductors sub-units of the Henry are used to denote its value.

The voltage across inductor is given by:

V = L di/dt

Where, L is the self inductance and di/dt is the rate of change of current.

The current through an inductor is given by:

I = 1/L ∫V.dt

The energy stored in an inductor is given by:

W = Li²/2