Electrical impedance
As indicated by the formulas above, the impedance varies depending on the frequency, for example, at zero Hertz, or DC, the impedance of the inductor is zero, the same as a short-circuit, and the impedance of the capacitor is infinite, the same as an open-circuit. Most signals are the sum of many sine waves at various frequencies (see the fourier transform for more details), and each of them experience a different impedance.