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Also see current, voltage, and direct current. In electricity, alternating current (AC) occurs when charge carriers in a conductor or semiconductor periodically reverse their direction of movement. Household utility current in most countries is AC with a frequency of 60 hertz (60 complete cycles per second), although in some countries it is 50 Hz. The radio-frequency (RF) current in antennas and transmission lines is another example of AC. An AC waveform can be sinusoidal, square, or sawtooth-shaped. Some AC waveforms are irregular or complicated. An example of sine-wave AC is common household utility current (in the ideal case).
Three cycles of an idealized North American 115 VAC, 60 Hz alternating current signal (black curve). Note that each cycle represents 16.67 milliseconds of time, because that is 1/60th of a second. curve actually goes from -170 V to +170 V in order to provide the average (RMS) value of 115 V.