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Vtile · (This post was last modified: 08-09-2021 05:53 PM by Vtile.)

IDEAL capacitor do block DC current as such allows AC current. Electronics as theory, like most theories them self is simplification of true world.

However, one question is that what is AC current. If something would change instantly the energy of such thing would be infinate. When capacitor charges it does not charge instantly there is a curve on voltage and current, what does happen is that in fact while charging the capacitor from DC current the actual thing that happen (slope) do have AC component (transient). The theory says AC does go through so what happens when you charge capacitor plates (electric field) from DC source?

The typical model which mostly is used as electronics and electrical analysis, is as known as centralised theory (iirc from work of Proteus Steinmetz), which assumes DC steady state (even witch AC). This is one reason GHz and above frequencies are sometimes considered as black magic. In fact many (persons who do practise the field) do say capacitors should be modeled as transmission line (one de-centralised theory).

This opinion is actually reasonable easy to rationally explain. If we assume that speed of light in vacuum is the speed limit of universe (approx. 300000000m/s), which is equivalent of velocity of 3.33 nanoseconds per meter. We also know that electricity is form of electromagnetic radiation. We also know that speed of light in another medium is always less than in vacuum (propagination factor). Now we have capacitor formed from two plates, whose dimensions are 0.01x1meters and contact point is at one end of plate. Propagination factor of plates is 1.5. In this case it takes 5 nanoseconds for the electric radiation to reach the another end of plate. This is of course simplification.

It is true dielectric can be also vacuum, then capacitor do not have dielectric absorption effect (slow dipoles in dielectric).

Electrons flow in circuit is considerably slower that electric field.

Unfortunately I notice my memory starts to deprecate on this fascinating subject.