Self Inductance
Whenever you change the current in a coil of wire, the magnetic field it produces will change. That will change the magnetic flux through the coil and hence produce a voltage across the coil. This phenomenon is called self-inductance, and the coil is referred to as an inductor.
The quantitative measure of this effect is the inductance
L
defined by
An inductor can store energy. The power (= energy / time) being
stored in an inductor is
This implies (by a little calculus) that the energy stored in an
inductor is
As an example, we can derive the inductance of a solenoid. The magnetic
field inside a solenoid of length
Therefore, the inductance L can be given in terms of the geometry of the solenoid.
Longer solenoids and solenoids with more cross-sectional area have more inductance. The strongest dependence is on the number of turns per unit length. One can also increase the inductance by using iron instead of a vacuum; in that case, the parameter m0 would be replaced by a larger value m .