The term DC is used to refer to power systems that use only one polarity of voltage or current, and to refer to the constant, zero - frequency, or slowly varying local mean value of a voltage or current. For example, the voltage across a DC voltage source is constant as is the current through a DC current source. The DC solution of an electric circuit is the solution where all voltages and currents are constant. It can be shown that any stationary voltage or current waveform can be decomposed into a sum of a DC component and a zero - mean time - varying component; the DC component is defined to be the expected value, or the average value of the voltage or current over all time.
what is the frequency of a dc voltage
zero zero