What does an open circuit on a line look like on a test?

• A. Short circuit with loud current flow.
• B. Infinite resistance and no signal on the line.
• C. Normal resistance with a continuous signal.
• D. Low resistance and strong signal.

Answer: (B)

An open circuit means there is a break in the conducting path of the line, so no current can flow. On test equipment this presents as infinite resistance because there’s no complete path for current. Since no current reaches the line to energize the headset, there will be no signal. The other scenarios describe faults or proper operation: a short circuit shows very low resistance with heavy current; a healthy line shows normal resistance with a continuous signal; a near-short with strong signal isn’t an open. So infinite resistance with no signal is the correct depiction of an open circuit.