alternating current

American  

noun

1. an electric current that reverses direction at regular intervals, having a magnitude that varies continuously in sinusoidal manner. ac

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alternating current British  

noun

1. Compare: direct current.   AC.  a continuous electric current that periodically reverses direction, usually sinusoidally

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alternating current Scientific  

/ ôl′tər-nā′tĭng /

1. 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.

2. Compare direct current See Notes at current Tesla

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alternating current Cultural  

1. An electric current (see also current) in which the flow reverses periodically. (Compare direct current (DC).)

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Discover More

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

Compare meaning

How does alternating-current compare to similar and commonly confused words? Explore the most common comparisons:

• direct current vs. alternating current

Example Sentences

To transform the medium-voltage alternating current that the grid serves to most end users into higher-voltage direct current, Nvidia suggests companies use solid-state transformers instead of the old kind.

From Barron's • Jun. 4, 2026

The solution emerged in the late 1880s through the bitter "War of the Currents," when George Westinghouse and Nikola Tesla championed alternating current.

From The Wall Street Journal • Apr. 24, 2026

Researchers used what is called "transcranial alternating current stimulation" to modulate brain activity.

From Science Daily • Mar. 15, 2024

The Boat Time YouTubers have invested in a more efficient inverter, which turns the direct current generated by their solar panels into the alternating current used by the grid.

From BBC • Aug. 21, 2023

The lamps that laced every building and walkway produced the most elaborate demonstration of electric illumination ever attempted and the first large-scale test of alternating current.

From "The Devil in the White City" by Erik Larson