*What is Self Inductance? Definition and Explaination*

*What is Self Inductance? Definition and Explaination*

**The coil opposes the change of current flowing through it.This property of the coil is called Self- Inductance. The opposition offered by a coil depends on the rate of change of the current. The more the rate of change of current, the more the opposition. Why this opposition of current take place? The opposite polarity voltage is induced across the coil and the magnitude of the voltage induced across the coil depends on the rate of change of current and the self inductance of the coil. The induced EMF in a coil always opposes the applied voltage.**

The voltage induced in the current carrying conductor is

## **Expression for Self Inductance**

The self inductance of the coil can be found by following expression.

If e= 1 Volt, dI/dt = 1 amp/sec, then L= 1 Henry

The coil has inductance of 1 Henry, if voltage induced in the coil is 1 volt when the current flowing through the coil changes at a rate of 1 Ampere/second.

The basic unit of inductance is Henry(H) after Joseph Henry.

** 1 Henry = 1 Weber per Ampere**

**Solved problems of self Inductance**

**In a coil, when current current changes from 5 A to 2 A in time 0.1 s,induced EMF is 3 Volts. What is the self inductance of the coil?**

E=-L(dI/dt)

3=-L[(2–5)/(0.1–0)]

3= -L(-3/0.1)

3 = 30 L

L= 3/30

**L = 0.1 Henry**

**What is the self inductance of a coil when a change of current from 0 to 1A in 0.05s induces an emf of 20 volts?**

E=-L[(I2-I1)/(t2-t1)]

20=-L[(0–1)/(0.05–0)]

20= -L(-1/0.05)

20 = 20 L

L= 20/20

**L = 1 Henry**

**An inductor coil has 400 turns of copper wire which produce a magnetic flux of 20mWb when DC current 10 amperes flows through the coil. What is the self inductance of the coil?**

Φ = 20mWb= 20 x 10

^{-3}

^{ }

^{= 0.02 Wb}

**Φ**/ I

**L= 0.8 Henry**

**The self inductance of a coil can also be expressed as;**

I = Current flowing through the coil

**Factors on Self Inductance Depends **

^{-7 })

**1. Permeability of the core**

2. Number of turns in a coil

3. Cross section area of the coil wire

4. Length of the coil

2. Number of turns in a coil

3. Cross section area of the coil wire

4. Length of the coil