What is the characteristic of alternating voltage?

The characteristic of alternating voltage is that it can periodically reverse direction. Alternating voltage, or AC voltage, is defined by its ability to change polarity and flow in both directions over time. This is a fundamental feature of AC, making it suitable for various applications, especially in power transmission and distribution systems. As a result, alternating voltage is utilized for most household and industrial electrical systems, providing a versatile means of delivering energy.

In contrast, the other choices describe characteristics that do not apply to alternating voltage. For instance, a constant voltage over time refers to direct current (DC), which maintains a steady voltage without reversing. The mention of unidirectional flow also pertains to DC, as it is the type of current that flows in only one direction. Lastly, the application of voltage solely in DC circuits is incorrect since alternating voltage is widely used in AC circuits. Understanding these distinctions is crucial for grasping the fundamental differences in electrical theory and the functioning of various electrical systems.