Inductors

When there is a current in the inductor, a magnetic field is created. Any change in current causes the magnetic field to change, this in turn induces a voltage across the inductor that opposes the original change in current.

A length of wire turned into a coil works as an inductor.

Inductance (L)

For an ideal inductor:

Here the is the voltage difference between the inductor, and is the current through the inductor.

The polarity is such as to oppose the change in current.

Energy stored

Suppose voltage across an inductor rises from to during a time period of seconds.