What is a key characteristic of alternating current?

A key characteristic of alternating current (AC) is that it changes polarity 60 times per second, which corresponds to a frequency of 60 Hertz. This means that the electric current flows in one direction for a certain amount of time and then reverses direction, creating a continuous back-and-forth flow of electric charge. This characteristic is crucial for the operation of many electrical systems and devices, as it allows for the efficient transmission of electricity over long distances and enables the use of transformers to step voltage levels up or down.

In contrast, if current were to travel only in one direction, it would be classified as direct current (DC). The requirement for a transformer is not inherent to alternating current; while AC does utilize transformers for voltage conversion, it is not essential for the existence of AC itself. Additionally, AC does not maintain a constant voltage; it varies sinusoidally with time, which is fundamental to its alternating nature.