Direct and alternating current. An oscilloscope displays the potential difference from an alternating current (AC) source and a direct current (DC) source. The AC source on the right produces the sine wave, whereas the DC source produces a flat, constant, voltage. This has been set to be at the root mean square (RMS) value of the AC source. That is, it is at the value of the average absolute potential difference in the AC circuit. The average power produced by an AC source is the same as that of a DC source of the same current but with voltage at its RMS value. Hence the two lightbulbs are the same brightness.