What distinguishes an arc from a spark?

The correct option highlights that an arc is specifically characterized by its length and duration compared to a spark. An arc refers to a continuous discharge of electricity that occurs across a gap and can sustain itself over a greater distance, while a spark is typically a brief and sudden discharge of electricity.

In contrast to the misconception that sparks could be analogous to thrown metal particles, the distinction lies in the nature of the electrical discharge. An arc can generate significant heat and maintain a flow of current, leading to a lasting plasma state, whereas a spark is a fleeting event that does not persist. Therefore, the critical difference is that arcs are longer and sustained discharges, indicating a more robust and continuous electrical flow. This understanding is essential for recognizing the distinctive features of electrical phenomena in contexts such as fire investigations.