If a component in a circuit is opened, an ohmmeter reading across the network tends to be:

• A. Infinite resistance.
• B. Zero ohms.
• C. Twenty ohms.
• D. One megaohm.

Answer: (A)

Opening a component breaks the conducting path, so there is no complete path for current to flow. An ohmmeter applies a test voltage and measures the current to calculate resistance (R = V/I). When the circuit is open, the current is essentially zero, so the calculated resistance becomes infinite. Practically, the meter will show OL or a reading indicating infinite resistance. This contrasts with a short (near zero ohms) or a real finite resistance (like twenty ohms); even a very large finite value, such as one megaohm, isn’t appropriate here because the open circuit prevents any current flow at all.