Which type of current periodically reverses direction?

Alternating current (AC) is the type of current that periodically reverses direction. This means that the flow of electric charge changes its polarity over time, flowing in one direction during one phase of the cycle and then reversing to flow in the opposite direction in the next phase. This alternating pattern is represented as a sine wave in electrical diagrams, which helps to visualize the change in direction and magnitude over time.

In contrast, direct current (DC) flows only in one direction, maintaining a constant polarity. Constant current refers to a current that remains unchanged over time but does not involve directional reversals. Pulsating current, while it varies in amplitude and can change at certain intervals, does not inherently reverse direction like alternating current does. Thus, the characteristics of AC make it particularly suitable for power distribution systems and many electronic devices, further clarifying why alternating current is the correct answer in this context.