**Chapter-6|Electromagnetic Induction (EMI)| NCERT 12th Physics:**

**Self Inductance:**

When a current flows through a coil, it produces magnetic field around it. When current changes, the magnetic field which is linked with the coil get changes, then flux will be change. Any change in flux will produces EMF. This phenomena of getting EMF is called self induction and this EMF is called self induced EMF.

In other words, If we change current in a coil, magnetic field changes and magnetic flux linked with the coil changes. This gives birth to induced EMF and induced current in the same coil, This phenomenon is called self inductance.

Let a coil of N turns carrying a current I. Let ΦB be the magnetic flux linked with the each turn of the coil.

The total flux linked with coil = NΦB

**Note: **L do not depends on ΦB or I. It depends upon dimensions, shapes, size of the coil, like resistance(R=V/I) and capacitance(C=Q/V).

If I=1A, then L=NΦB

Hence, the coefficient of self induction of a coil is equal to the number of magnetic flux linkage with the coil, when unit current is flowing through the coil.

If on changing the current in the coil, the back EMF induced in the coil be e, then by Faraday’s law.

The coefficient of self induction of a coil is numerically equal to the EMF induced in the coil, when the rate of change of current in the coil is unity.

* Self inductance opposes the change in current like inertia opposes the change in state, so it is also called inertia of electricity.

**Coefficient of Self Inductance of a Solenoid:**

Let l= Length of solenoid

A= Area of each turn of the solenoid

I= Current flows in solenoid

N= Total number of turns

n= Number of turns per unit length, Then

N= nl

Note: L depends on dimensions, shape and size of the coil.

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