**Coefficient of self induction**

When a current I flows through a coil, the magnetic flux (φ) linked with the coil is proportional to the current.

**φ α I or φ = LI**

where L is a constant of proportionality and is called coefficient of self-induction or self-inductance.

If I = 1A, φ = L × 1, then L = φ Therefore, the coefficient of self-induction of a coil is numerically equal to the magnetic flux linked with a coil when unit current flows through it. According to laws of electromagnetic induction.

**e = – dφ/dt = d/dt (LI)**

**or, e = – L (dI/dt)**

**If (dI/dt) = 1 A s ^{-1}, then L = − e**

The coefficient of self induction of a coil is numerically equal to the opposing emf induced in the coil when the rate of change of current through the coil is unity. The unit of self inductance is henry (H).

One henry is defined as the self-inductance of a coil in which a change in current of one ampere per second produces an opposing emf of one volt.