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Q&A What reactance actually is?

Reactance is the lossless part of impedance that stores and releases energy E=1/2 LI^2 or 1/2CV^2 . Much like a spring stores energy when compressed or expanded. L is a conductor that stores curr...

posted 2y ago by TonyStewart‭

Answer
#1: Initial revision by user avatar TonyStewart‭ · 2022-04-09T17:52:51Z (over 2 years ago)
Reactance is the lossless part of impedance that stores and releases energy E=1/2 LI^2 or 1/2CV^2 .  Much like a spring stores energy when compressed or expanded.

L is a conductor that stores current with charges flowing. Q=LI.

C is an insulator with some dielectric constant , Dk, relative to air measured with stationary charges Q=CV.

Losses are maybe modelled in series as DCR in L, or ESR in C when current flows with a source and/or load.  Without this there may be a shunt leakage loss in C.  For L as a conductor, such parallel R might be the work done by any moving solenoid or motor as P=V^2\R such that with no load or friction it is inductive mainly and only if you exclude DCR.

All conductors have inductance per unit length and increases when coiled and amplified when near high permeability material.
Since conductors have insulation around them , they also have capacitance to the nearest conductor.  Reactive or "characteristic" impedance is known here as Zo=sqrt(L/C) . This applies equally to lumped parts and "all "Transmission Lines", coax,CAT5, UTP etc...