alternating current(n = noun.phenomenon) ac, alternating electric current - an electric current that reverses direction sinusoidally; "In the US most household current is AC at 60 cycles per second"
is a kind of electrical energy, electricity
Antonym: direct current

   A current which periodically changes or reverses its direction of flow, especially an electric current that reverses direction sinusoidally, as is used for most domestic and industrial power requirements. Contrasted with direct curent. [Webster 1913 Suppl.]
"The common household current is alternating. Alternating current is easier than direct current to transform to high voltage and back, making long-distance transmission more efficient." [PJC]

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