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Hello everyone, I'm new to this forum and electronics. I am teaching myself from the Electronics Fundamentals text by Floyd. It's a great book, although it occasionally leaves a question unanswered. I am also using MultiSim 10.1 to build and test circurts. My question is as follows:

If a capacitor an an AC circut alternately stores enegry and returns energy to the source it seems to me that the capacitor is only useful 50% of the time. I say this in reference to a DC capicator which in theory holds a charge until it's used. So if you remove the voltage source in an AC circut the capacitor may or may have a charge. I'm sure there is a good reason, could some one please explain.

Thanks in advance for any help in this matter......


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Most Helpful Member
You have the right idea, but I take issue with the "50% useful" statement. Since the goal of putting a capacitor in an AC circuit is to provide a path for an AC current, it is "useful" 100% of the time, regardless of the instantaneous state of charge at any given instant.

As to leaving a capacitor charged if it is suddenly disconnected from an AC circuit, yes, that can leave the capacitor charged with either polarity. It is common practice to put a high-value resistor across a capacitor in an AC Power circuit to discharge it (bleeder resistor) to minimize shock hazard...


Even an uncharged capacitor is useful. It lies in wait to accept excess charge that is undesirable in the curcuits 'downstream.' It is ready to pass a signal while blocking and DC that might be present. Or it might be cooperating with other elements in the circtuit to produce a signal, which just happens to be at the zero crossing level. Leave the caps in the circuit. They are always useful :D
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