Question 5: Explain the phenomenon of self-induction. Define the coefficient of self-induction and units?

## Definition of self-inductance

“Self-inductance (or simply inductance) is the property of a coil which opposes any changes in the amount of current flowing through it.”

This happens due to the self-induced emf in the coil by changing the current flowing in it.

#### Explanation of self-inductance

Consider a coil of N turns as shown in the figure. Let the AC current flowing in the coil is I. When the current flowing in the coil changes then the magnetic flux linking the coil also changes. This will set up an emf, called induced emf ε, in the coil. By Faraday’s Law

Here ∆Ф is the change in the linking flux in small interval of time ∆t. N is constant.

Now the flux linking the coil of N turns is proportional to the current in the coil.

By putting in the above equation (1).)

Here L is the coefficient of self-inductance or self-inductance.

#### Definition of coefficient of Inductance

From the above equation, coefficient of inductance L is,

Therefore, this can be defined as, “the ratio of the induced emf ϵ to the rate of change of current through the coil”.

Similarly, compare (1) and (2). So coefficient of inductance of a coil may be alternatively defined as the ratio of flux linkages of the coil to the current flowing in it.

#### Unit of inductance

Its unit is henry, denoted by H and is equal to volt. second per Amp. It can be defined as “The inductance of a coil is 1 H if an emf of 1 volt is induced in it when current through the coil changes at the rate of 1 ampere per second.”