alternating current
Americannoun
noun
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An electric current that repeatedly changes its direction or strength, usually at a certain frequency or range of frequencies. The term is also used to describe alternating voltages. Power stations generate alternating current because it is easy to raise and lower the voltage of such current using transformers; thus the voltage can be raised very high for transmission (high voltages lose less power as heat than do low voltages), and lowered to safe levels for domestic and industrial use. In North America, the frequency of alternation of the direction of flow is 60 Hz, or 60 cycles per second. In other parts of the world it is 50 Hz.
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Compare direct current See Notes at current Tesla
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In the United States, most household current is AC, going through sixty reversal cycles each second. Electric motors in household appliances are designed to work with current at this rate of reversal.
Etymology
Origin of alternating current
First recorded in 1830–40
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Example Sentences
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
For efficiency reasons, data centers are transitioning to using more direct current, or DC, electric systems, as opposed to the alternating current that most of the broader electric grid uses.
From Barron's • Apr. 29, 2026
Unlike DC, alternating current could travel vast distances before being safely lowered for household use.
From The Wall Street Journal • Apr. 24, 2026
In conventional devices, microwave radiation induces an additional alternating current through the Josephson contact.
From Science Daily • Dec. 23, 2025
One of the first West Coast reinforced concrete structures, the steam plant originally powered the Interurban Railway between Seattle and Tacoma and supplied direct current for Seattle streetcars and alternating current for Georgetown.
From Seattle Times • Oct. 26, 2023
On the other side was Westinghouse Electric Company, with a bid to wire Jackson Park for alternating current, using patents that its founder, George Westinghouse, had acquired a few years earlier from Nikola Tesla.
From "The Devil in the White City" by Erik Larson
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
