Self inductance

SELF INDUCTANCE

Consider a circuit through which the current changes. So, the flux linking with the circuit also changes. According to Faraday's law of induction an e.m.f. is induced in the circuit. This e.m.f. is equal to rate of change of flux linkage.

i.e., e = N dϕ / dt ... (1)

Also e is proportional to time rate of change of current i.e., e∝ di / dt.

(or) e = L di/dt … (2)

From equations (1) and (2), we can write,

L di/dt = N dϕ / dt … (3)

(or) L = N dϕ/di …. (4)

If the permeability is constant then, we can write that,

L = Nϕ/I .... (5)

ubai A

L is called self inductance of the circuit.

Definition of L

The self inductance of a coil is defined as flux linkage in that coil per 1 ampere current in the same coil. It is also defined as the weber turns per ampere current in the coil. L is measured in Henry.

Here, N = No. of turns of the coil

ϕ = Magnetic flux in webers

i = current in amperes

[Note: (i) According to Lenz's law, - sign is to be given to the right hand side of the expressions shown in equations (1) & (2).

(ii) The terms N, & and i are confined to only one coil to define 'L']