What type of current periodically reverses direction in an electrical circuit?

Alternating current periodically reverses direction in an electrical circuit.

In an alternating-current system, the voltage and current typically vary with time, often in a sinusoidal pattern. The most common power-grid waveform repeatedly changes polarity, allowing energy to be transmitted and distributed through transformers.

Direct current, by contrast, maintains one direction of flow. Batteries supply direct current, while household outlets in many countries supply alternating current. Electronic devices often convert incoming alternating current to direct current using rectifiers and power supplies.

Nikola Tesla and George Westinghouse were major figures in the development and promotion of alternating-current systems during the late nineteenth century. The practical advantage of AC transmission is that transformers can efficiently raise voltage for long-distance transmission and lower it for consumers. Frequency varies by region; 50 and 60 hertz are the two dominant standards.