Alternating current

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In alternating current (AC, also ac) the movement of electric charge periodically reverses direction. In direct current (DC), the flow of electric charge is only in one direction.

AC is the form in which electric power is delivered to businesses and residences. The usual waveform of an AC power circuit is a sine wave. In certain applications, different waveforms are used, such as triangular or square waves. Audio and radio signals carried on electrical wires are also examples of alternating current. In these applications, an important goal is often the recovery of information encoded (or modulated) onto the AC signal.

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History

The first inventor to use alternating current was apparently Guillaume Duchenne, the developer of electrotherapy. In 1855, he announced that alternating was superior to direct current for electrotherapeutic triggering of muscle contractions.[1]

A power transformer developed by Lucien Gaulard and John Dixon Gibbs was demonstrated in London in 1881, and attracted the interest of Westinghouse. They also exhibited the invention in Turin in 1884, where it was adopted for an electric lighting system. Many of their designs were adapted to the particular laws governing electrical distribution in the UK.[citation needed]

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