What is the primary distinction between alternating current (AC) and direct current (DC)?

The primary distinction between alternating current (AC) and direct current (DC) lies in how the current flows. AC is characterized by its ability to change direction periodically, which means that the flow of electric charge reverses back and forth. This alternating nature allows AC to be transmitted over long distances more efficiently than DC, which flows in a single, unidirectional manner.

When evaluating the answer choice provided, stating that AC flows in a single direction is not accurate, as it is actually DC that flows in this way. Therefore, recognizing that AC alternates direction is essential in understanding how AC operates in power systems.

Additionally, focusing on the other aspects helps clarify the differences. AC voltage can vary greatly, typically represented as an oscillating waveform, while DC maintains a constant voltage level over time. DC is often utilized in low-voltage applications such as batteries, whereas AC is more commonly employed for power transmission in homes and industries due to its efficiency in handling high voltage over distances. Thus, understanding these fundamentals provides a comprehensive view of the significant operational characteristics that differentiate AC from DC.