Unit of inductance- self-inductance and mutual inductance- is Henry, abbreviated as H. It is named after the American physicist Joseph Henry. Most electrical coils have inductance properties. The change in the electric current or flux induces EMF in a coil. This property is called inductance.
The magnitude of induced EMF is proportional to the rate of change of the electric current. The higher rate of change of current causes more flux. As a result, more EMF induces in a coil.
The S.I unit of the inductance is Henry H. Its MKS unit is Kg m² s⁻² A⁻².
Definition of Henry
When a coil receives an alternating current, the flux induces in a coil. The varying flux induces EMF in a coil. The following formula shows the relationship between induced EMF and the rate of change of current.
From the above formula of inductance, if one volt induces in a closed circuit or a coil by variation of alternating current of 1 ampere per second, then the self-inductance of a coil is one Henry.
We can express Henry in another form as given below.
In the case of two coils mutually coupled, the mutual inductance of the coils is as below;
The mutual inductance(M) of mutually coupled coils is one henry if a varying current of 1 ampere per second in one coil induces one volt in another coil.
Thus, the SI unit of inductance is Henry(H).
Other units of Inductance
Henry is the big unit of inductance. There are other smaller units of inductance, such as millihenry(mH), micro-Henry(μH), and nano-Henry(nH).
The inductance of a coil having a value in the order of millihenry(mH) and micro-Henry(μH) has wide applications for radio and audio frequency range.
The inductance of a coil having a value in the order of nano-Henry(nH) has wide applications for a very high-frequency range.
Relation between the Different units of Inductance
| Units of Inductance | Units in Henry |
| 1 millihenry(mH) | 10-3 H |
| 1 micro-Henry | 10-6 H |
| 1 nano-Henry | 10-9 H |
| 1 pico-Henry | 10-12 H |