I understand that capacitors will charge until it’s “full” and voltage and current = 0 because no more electrons can go through. In AC circuits, capacitors will charge and discharge according to the ups and downs of the sin graph. But how does this filter noise?
Noise being different frequencies than the sin wave that we want?
In: Physics
A capacitor can accommodate AC signals because, as you say, they fill and empty and refill. It turns out this isn’t a binary thing, where DC is blocked and anything wave-shaped sails right through.
The impedance of a capacitor is 1/jωC where ω is the angular frequency of the signal and C is the capacitance. So if you have a really high-frequency signal the impedance is tiny, low-frequency sees higher impedance, and DC’s frequency is effectively zero so it sees a capacitor as an open circuit/brick wall.
So the higher frequency you are, the more capacitive circuits like you; you can use capacitance to make a “high-pass” filter where high frequencies go through and low freq/DC gets blocked. With inductors you can make low-pass filters which do the opposite (friendly to DC, block high frequency) and by combining those we can make band-pass filters where too high *and* too low freqs get blocked.
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