Question

Define self-inductance of a coil interms of

1. magnetic flux and
2. induced emf

Answer 1

Self-inductance or simply inductance of a coil is defined as the flux linkage of the coil when 1A current flows through it.
When the current i changes with time, an emf is induced in it. From Faraday’s law of electromagnetic induction, this self-induced emf is given by

`epsilon = - ("d"("N"Φ_"B"))/"dt" = - ("d"("Li"))/"dt"`

`therefore epsilon = - "L" "di"/"dt"` or L = `(- epsilon)/("di"//"dt")`

The negative sign in the above equation means that the self-induced emf always opposes the change in current with respect to time. If `"di"/"dt"` = 1 As^-1, then L = - ε.
Inductance of a coil is also defined as the opposing emf induced in the coil when the rate of change of current through the coil is 1 A s^-1.