What is the definition of Alternating Current (AC)?

Alternating Current (AC) is defined as a current that switches direction periodically. This means that the flow of electricity alternates between positive and negative directions at regular intervals, which is characteristic of AC systems used in most residential and commercial power supplies. The periodic switching allows for efficient energy transmission over long distances and enables the use of transformers to change voltage levels.

In contrast, a current that flows in one direction only is known as Direct Current (DC), which is typically used in batteries and electronic devices. The choice referring to constant voltage conveys a trait more aligned with specific power supply types rather than the nature of AC itself. Lastly, the idea that AC decreases resistance does not accurately represent its function or characteristics; rather, resistance pertains to the material's properties affecting the current's flow but does not define the current type. Therefore, the definition that captures the essence of AC is the one noting its ability to switch direction periodically.