To measure resistance using an ohmmeter, the part must be

• A. Connected In The Circuit
• B. Isolated From The Circuit
• C. Grounded
• D. Powered

Answer: (B)

An ohmmeter works by sending a small test current through the part and measuring the resulting voltage to calculate resistance (R = V/I). For this to reflect the part’s true resistance, the component must be isolated from the rest of the circuit. If it stays connected, other paths—resistors, junctions, or even powered devices—alter the current distribution and the voltage that the meter reads, giving a reading that corresponds to a network rather than the individual part. To obtain an accurate measurement, power off the circuit and disconnect at least one lead so the meter only probes the component itself. Grounding or keeping it in the circuit would also distort the reading, and measuring while powered can damage the meter and the circuit.