• The AC impedance of a capacitor is called capacitive reactance. It decreases with increasing frequency. While Ohm's Law applies directly to resistors in DC or in AC circuits, the form of the current-voltage relationship in AC circuits in general is modified to the form: where I and V are the rms or "effective" values. The quantity Z is called impedance. For a pure resistor, Z = R. Because the phase affects the impedance and because the contributions of capacitors and inductors differ in phase from resistive components by 90 degrees, a process like vector addition (phasors) is used to develop expressions for impedance. More general is the complex impedance method.
  • 5-29-2017 It takes a few weeks to explain the basic concepts, and then it only takes one sentence to answer your question. Here is a free course in the basics: The answer is there is no dc current path through the capacitor. But you have to understand what impedance is for that to mean anything.

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