Which feature distinguishes AC from DC in terms of polarity?

The distinguishing feature between alternating current (AC) and direct current (DC) in terms of polarity is that DC has a constant direction of flow. In a DC circuit, the electric charge flows in one direction only, maintaining a consistent polarity. This is characteristic of battery-powered devices, where the positive and negative terminals do not change, resulting in a continuous and stable flow of electricity in the same direction.

In contrast, AC changes its direction periodically. The polarity of AC switches between positive and negative, meaning its current alternates rather than flows steadily in one direction. This alternation leads to the varying voltage levels observed in AC systems. The fact that DC maintains a constant direction is what fundamentally sets it apart from AC regarding polarity.