Which measurement is primarily used to detect an open circuit?

• A. Resistance
• B. Voltage
• C. Current
• D. Capacitance

Answer: (A)

Detecting an open circuit is all about continuity and resistance. An open path means there is no complete route for current, so the resistance along that path becomes effectively infinite. The best way to confirm this is to measure resistance with a meter in the ohms/continuity mode. If you read an extremely high value or OL, that indicates the circuit is open. If the resistance is low, the path is continuous; if it were near zero, you’d have a short instead.

Voltage measurements aren’t the primary tool here because they show potential difference, not whether the path is complete. A powered circuit could still display a voltage at a point even if part of the path is open, so it doesn’t reliably reveal continuity. Current measurement also isn’t ideal for diagnosing an open circuit, since it requires a closed loop to flow; asking a meter to read current in an open path simply yields zero, which doesn’t distinguish between a powered open circuit and a deliberately open one. Capacitance isn’t used to test for an open path and doesn’t indicate whether a circuit is continuous.

So, resistance measurement directly reveals whether the path is open: a very high or infinite reading signals an open circuit.