What defines a "circuit" in an electrical system?

A "circuit" in an electrical system is defined as an unbroken path through which current flows. This description captures the fundamental principle of how electrical circuits operate. For current to flow, there must be a continuous loop that allows electrons to move from a power source, through various components, and back to the source. The clarity of this definition is essential because it underscores the necessity of an uninterrupted pathway; any disconnection in this path would prevent current from flowing, thereby ceasing the operation of the circuit.

The other options do not accurately portray the definition of a circuit. A disconnected current source refers to a state where power cannot flow, which does not represent the concept of a circuit. A device that controls voltage relates to circuit components such as transformers or regulators but is not a definition of a circuit itself. Similarly, a protective element for equipment, like fuses or circuit breakers, serves to safeguard electrical devices but does not constitute the definition of a circuit. Understanding a circuit as an unbroken path is crucial for grasping how electrical systems function.