Which of the following best describes an open circuit?

• A. A circuit path that is not complete, so no current flows
• B. A circuit with zero resistance
• C. A closed loop with minimal resistance
• D. A perfectly balanced network

Answer: (A)

An open circuit happens when the conducting path is not complete, so the current cannot complete its loop back to the source. For current to flow, there must be a closed loop from the power source through the loads and back. When there’s a break—a switch left open, a broken wire, or a gap—the path isn’t continuous, the circuit’s effective resistance becomes infinite, and no current can flow despite the source applying a potential difference. You can think of the source trying to push electrons, but the break stops them, so the circuit sits “open.”

This is different from a circuit with zero resistance, which would create a short and drive a large current. It’s also different from a closed loop with minimal resistance, which would allow current to flow readily. And a perfectly balanced network describes a condition where voltages cancel in a bridge or network, not the presence or absence of a complete path.