Increase in current expands the field & decrease in current reduces it. A
change in current produces
change in the electromagnetic field. This induces a voltage across the coil according to Faradays laws of
Electromagnetic Induction.
Induced Voltage V = L
V = Voltage across inductor in volts
I = Current through inductor in amps
di = v dt
Integrating both sides,
Power absorbed by the inductor P = VI = Li
Energy stored by the inductor
W=
=
dt =
W =
Conclusions:
1) V = L
The induced voltage across an inductor is zero if the current through it is constant. That
means an inductor acts as short circuit to dc.
2) For minute change in current within zero time (dt = 0) gives an infinite voltage across the
inductor which is physically not at all feasible. In an inductor, the current cannot change abruptly. An
inductor behaves as open circuit just after switching across dc voltage.
3) The inductor can store finite amount of energy, even if the voltage across the inductor is zero.
4) A pure inductor
never dissipates energy, it only stores it. Hence
it is also called as a non
–
dissipative passive element. However, physical inductor dissipates power due to internal resistance.
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