Inductance is a measure of the amount of magnetic flux produced for a given electric current. The term was coined by Oliver Heaviside in February 1886. The SI unit of inductance is the henry (symbol: H), in honour of Joseph Henry. The symbol L is used for inductance, possibly in honour of the physicist Heinrich Lenz.
The inductance has the following relationship:
where; L is the inductance in henrys, i is the current in amperes, Φ is the magnetic flux in webers. Strictly speaking, the quantity just defined is called self-inductance, because the magnetic field is created solely by the conductor that carries the current.
When a conductor is coiled upon itself N number of times around the same axis (forming a solenoid), the current required to produce a given amount of flux is reduced by a factor of N compared to a single turn of wire. Thus, the inductance of a coil of wire of N turns is given by:
where, is the total 'flux linkage'.