What characterizes alternating current (AC)?

Alternating current (AC) is characterized by its periodic nature, meaning it changes direction and varies in magnitude over time. Unlike direct current (DC), which flows continuously in one direction, AC flows back and forth, usually following a sinusoidal waveform. This oscillation results in an average value of zero over one complete cycle, as the positive and negative values effectively cancel each other out.

This understanding of the periodic nature of AC is crucial in various applications, including power generation and transmission, where AC is preferred for its ability to be transformed to different voltages efficiently. This characteristic also allows AC systems to distribute electricity over long distances with reduced energy loss compared to DC systems.

The other options provide incorrect characterizations of AC. Continuous flow in one direction describes DC, while a constant value does not apply to AC because its voltage and current continually vary. Lastly, stating that AC is only used in batteries is misleading, as batteries typically store and supply DC. AC is widely utilized in power grids, household appliances, and various electronic devices.