What is the key characteristic of a series circuit?

A series circuit is defined by the presence of a single path through which current flows. In this type of circuit, all components—such as resistors, capacitors, or bulbs—are connected end-to-end, so the same current flows through each component. If any part of the circuit fails or is disconnected, the entire circuit is interrupted, and current ceases to flow. This characteristic is fundamental to understanding how series circuits operate, distinguishing them from parallel circuits that allow for multiple paths for current flow.

The other aspects mentioned may apply to various circuits in general; however, they do not specifically identify the defining feature of a series circuit. For example, while series circuits can include either AC or DC components, this feature is not exclusive to them. Similarly, the requirement for a circuit breaker pertains to safety and circuit protection, not the basic operational nature of a series circuit.