What is a circuit?

• A. A device that converts energy into light.
• B. A closed loop with no potential difference.
• C. A single wire carrying current.
• D. A system of conductors and components in which current can exist.

Answer: (D)

A circuit is a system of conductors and components arranged so current can exist and flow when a source provides a potential difference. In practice, this means there’s a complete path for electricity to travel from a power source, through wires and parts like lamps or resistors, and back to the source. The key idea is having a path plus a source to push the current through.

The other ideas are incomplete for different reasons: a device that converts energy to light is just one component of a circuit, not the whole network; a closed loop with no potential difference won’t drive current, so there’s no flow; and a single wire carrying current isn’t a complete circuit unless there’s a source and a return path to complete the loop.