What is the main difference between AC and DC?

The main distinction between alternating current (AC) and direct current (DC) lies in the nature of how electricity flows. AC alternates direction, meaning that the current changes its flow periodically, allowing it to reverse itself back and forth. This characteristic is particularly useful for efficiently transmitting electricity over long distances, as it can be easily transformed to higher or lower voltages using transformers.

On the other hand, DC flows in one constant direction, providing a steady and unidirectional flow of electric charge. This makes DC more suitable for applications that require stable and constant voltage, such as batteries and electronic devices.

The other points offered in the choices provide some context but do not capture the fundamental difference as effectively as the alternation of current flow does. For instance, while it is true that AC can travel longer distances than DC due to its ability to be transformed to higher voltages (which minimizes losses during transmission), this is a consequence rather than a fundamental difference. Thus, the defining characteristic effectively underscores the operational distinction between AC and DC.