alternating current [AC]

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(n.) In the United States, 120-volt electricity delivered by utility companies. It changes polarity from positive to negative 60 times per second. In other countries, the rate of alternation is often 50 cycles per second (cps). Direct current (DC), by contrast, is a continuous stream of current in one direction with polarity. The regular pulse of AC can be picked up by audio systems that are not well grounded, introducing an undesirable 60-cycle hum. Compare direct current.