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
You can look at a capactor as a resistance with a low resistance at high frequency and high resistance at low frequency. In the case of DC it let nothing trough. To what degreree this happen at different freqiunsis depend on the capacitance of the
A simple filter do not filter out noise it blocks different frequencies to different amount. If you have a system where you for some reason have nose at a higher frequency then the signal you can filter it out with a filter that let low frequencies too and block high frequencies.
That would be called a low pass filter and a very simple open looks like [this](https://qph.cf2.quoracdn.net/main-qimg-7ab20326bdddb4a7a1e65322743ea15b) The capacitor let trough the high frequencies to ground but low frequencies continue on the upper line. You can look at it as a low frequency signal will change slow enough so the capacitor get changed to the same voltage with low delay compared to the length of a period. A high frequency signal will have a shorter period and then the capacitor will not get change fast enough so all change is used to change up the capacitor and do not pass on in the circuit
If you have noise at lower frequency then the signal you use a high pass filter and let the high frequencies trough. A simple filter will look like [this](https://qph.cf2.quoracdn.net/main-qimg-ac9b2cfe1b3c208700a1635062c40e8a)The resistor and capacitor is swapped.
Put a high pass filter after a low pass filter with appropriate component values and you can select a frequency range that can pass troug. That is called a band pass filter. [https://www.allaboutcircuits.com/uploads/articles/capacitive-band-pass-filter-circuit.png](https://www.allaboutcircuits.com/uploads/articles/capacitive-band-pass-filter-circuit.png)
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