Self-inductance is the ration between the induced electromotive force (EMF) across a coil to the rate of change of current through this coil. Self-inductance is related term to self induction phenomenon because self-induction generates self-inductance. We denote self-inductance or Co-efficient of with English letter L. Its unit is Henry (H). First, we have to know what self-induction is. Self-induction is the phenomenon by which in a coil, the change in electric current produces an induced electromotive force across this coil itself. This induced electromotive force (E) across this coil is proportional to the current changing rate. The higher the rate of change in current causes higher value of emf.
We can write that, But the actual equation is
Why there is Minus (-) sign? According to Lenz’s Law, this induced emf across this coil is always opposite to the direction of the rate of change of current. When the current (i) flows through a coil some electric flux produces inside the coil. At that moment of self-induction phenomenon, the induced emf generates to oppose this rate of change of current in that coil. So their values are same but sign differs.
Video Presentation of Self Inductance
But in AC circuit, the alternating effect of current always causes the self-induction in the coil, and a certain value of this self-inductance gives the inductive reactance (XL = 2πfL) depending on the value of supply frequency.
In the electrical circuit the coils those are used known as inductor having inductance values of L1, L2, L3 etc. and when they are series combined then equivalent inductance of them is calculated as When they are in parallel, then