Which type of current periodically changes direction in a conductor?

The correct answer is alternating current. Alternating current (AC) is characterized by the fact that its flow direction and magnitude change periodically over time. This is in contrast to direct current (DC), which flows consistently in one direction.

AC is commonly used in household electrical systems because it can be easily transformed to different voltages, making it efficient for long-distance power transmission. The periodic changes in the current direction are typically sinusoidal in nature, allowing for the efficient operation of electric motors and other devices.

The other types of current, such as direct current and steady current, maintain a constant direction and do not experience this periodic change. Static current is not generally a recognized term in electrical theory, as it implies a lack of movement rather than a changing flow of electricity.