Thread: AC Circuit
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Nov7-12, 10:33 PM
P: 25
Recently, I've been studying AC circuits and have developed a couple questions. I think I worked out an answer to the first, but I don't know about the second.

First, since light bulbs in houses are powered by AC current, why do we not see them flicker? Assuming they obey Ohm's law, the current through them is in phase with voltage, and so it must be 0 twice every period. My guess is that 60 Hz or 50 Hz used in most countries is simply so fast that our eyes don't register the flicker?

Second, this question concerns complex impedance and inductors/ resistors in circuits. Let's say we have a variable inductor in series with a resistor. Supposedly this is an example of a light-dimmer, because if we increase the inductance, then there is a larger voltage drop across it because its reactance is jωL. What I don't understand is that since the voltage is AC, and the voltage across an inductor is L*dI/dt, wouldn't there be points in the cycle that the voltage across the inductor drops to 0, and then the voltage across the light bulb should increase a whole lot! So at least momentarily, why don't light bulbs change brightness oscillating between lighter and dimmer?

I guess that question also implies the question as to how impedance can be jωL (a constant) even though there are different voltage drops at different times across the inductor.

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