An inductor is a passive two-terminal electrical component which resists changes in electric current passing through it. It consists of a conductor such as a wire, which is wound into a coil. When the current flowing through an inductor changes, the time-varying magnetic field induces a voltage in the conductor.

An inductor is characterized by its inductance. The inductance is the ratio of the voltage to the rate of change of current which has units of henries (H). Many inductors have a magnetic core made of iron or ferrite inside the coil. This serves to increase the magnetic field and thus the inductance.

Inductors are widely used in alternating current electronic equipment. They are also used to block the flow of AC current while allowing DC to pass. Inductors are designed for this purpose and are called chokes. They are often used in electronic filters to separate signals of different frequencies and in combinations with capacitors to make tuned circuits.

Inductance results from the magnetic field around a current-carrying conductor. The electric current through the conductor creates a magnetic flux proportional to the current. Any change in the current results in a voltage across the conductor which opposes the current change. The voltage across the terminal of an inductor is given by:

V = L (Di/dt)

Where

v is the voltage

L is the inductance

i is the current

t is the time