What is the main characteristic of Alternating Current (AC)?

The main characteristic of Alternating Current (AC) is that it reverses or alternates its direction of flow. In an AC circuit, the voltage and current vary periodically, typically in a sinusoidal wave pattern. This means that the electrical current changes direction at regular intervals, which allows it to be transmitted efficiently over long distances. This property of alternating flow is fundamental to how AC is generated and distributed, especially in residential and commercial power systems.

In contrast, options like flowing in one direction only reflect the behavior of Direct Current (DC), where the flow is unidirectional. Using AC for digital electronics is generally less common; digital electronics typically operate on DC for reliable logic state representation. Additionally, stating that AC is always constant misrepresents its nature, as its defining feature is its variability in voltage and current over time, rather than maintaining a constant flow. Thus, the alternating nature of AC is what distinctly defines it in electrical engineering.