<P> In alternating current ( AC ) systems , the movement of electric charge periodically reverses direction . AC is the form of electric power most commonly delivered to businesses and residences . The usual waveform of an AC power circuit is a sine wave . Certain applications use different waveforms , such as triangular or square waves . Audio and radio signals carried on electrical wires are also examples of alternating current . An important goal in these applications is recovery of information encoded ( or modulated ) onto the AC signal . </P>
the type of electrical current in which electrons flow first in one direction then in the other is
alternating