alternating current

American  

noun

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

---

alternating current British  

noun

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

---

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

---

alternating current Cultural  

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

---

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

In conventional devices, microwave radiation induces an additional alternating current through the Josephson contact.

From Science Daily • Dec. 23, 2025

Once the construction is completed, it will convert 1,250 megawatts of clean energy from direct current to alternating current power that will be fed directly into the state's power grid.

From Reuters • Sep. 19, 2023

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 transmission line’s direct-current section allows efficient, long-distance electricity transfer with no tie-ins to other power lines, while the alternating current segment is less efficient but connects to the rest of the grid.

From Seattle Times • Jun. 20, 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