What is alternating current (AC)?

Alternating current (AC) is defined as an electric current that reverses direction periodically. This characteristic is fundamental to the operation of most electrical systems and devices. In AC, the flow of electric charge changes direction at regular intervals, typically measured in hertz (Hz), which indicates how many times the current alternates per second.

This behavior contrasts with direct current (DC), where the electric charge flows in a single direction uninterrupted. In AC systems, the periodic reversal of current allows for the effective transmission of electricity over long distances and enables the use of transformers to step up or step down voltage levels. This makes AC particularly suitable for residential and commercial power distribution.

The other options do not accurately describe alternating current. An electric current that flows only in one direction corresponds to direct current, a constant current refers to DC as well but is characterized by its steadiness rather than periodic reversal, and short bursts of electrical flow describe more transient signals rather than a stable current form like AC. Thus, the definition of AC as an electric current that reverses direction periodically is essential for understanding its applications and behaviors in various electrical systems.