How filter capacitors work is based on the principle of capacitive reactance. Capacitive reactance is how the impedance (or resistance) of a capacitor changes in regard to the frequency of the signal passing through it. Resistorsare nonreactive devices. This means that resistors offer the same resistance to a. Being that capacitors have offer very high resistance to low frequency signals and low resistance to highfrequency signals, it acts as a high pass filter,. In the same way that capacitors can act as high-pass filters, to pass high frequencies and block DC, they can act as low-pass filters, to pass DC signals and block AC. Instead of placing the. To see how a capacitor acts as a filter, you can conduct an experiment with relative ease. All you have to do is take a capacitor, any value or.