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?
3 = 30 L
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?
20 = 20 L
L = 1 Henry
Φ = 20mWb= 20 x 10-3
= 0.02 Wb
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
2. Number of turns in a coil
3. Cross section area of the coil wire
4. Length of the coil