Which instrument would you use to measure resistance in a de-energized circuit?

Which instrument would you use to measure resistance in a de-energized circuit?

• A. Ammeter
• B. Ohmmeter
• C. Voltmeter
• D. Multimeter

Answer: (B)

Measuring resistance relies on an instrument that injects a known test current and reads how much voltage appears across the component. An ohmmeter is designed for this task: you connect its leads to the circuit after removing all power, and it applies a small current to determine the resistance value. In a de-energized circuit, this approach gives a clean resistance reading without interference from live power sources. The other tools don’t fit as directly: an ammeter measures current in a circuit, not resistance. A voltmeter measures voltage and wouldn’t provide resistance information on its own. A multimeter can measure resistance when set to the ohms range, but the device specifically built for resistance measurements is the ohmmeter, making it the best choice here. Always ensure the circuit is fully de-energized and any stored charge is discharged before measuring.

Measuring resistance relies on an instrument that injects a known test current and reads how much voltage appears across the component. An ohmmeter is designed for this task: you connect its leads to the circuit after removing all power, and it applies a small current to determine the resistance value.

In a de-energized circuit, this approach gives a clean resistance reading without interference from live power sources. The other tools don’t fit as directly: an ammeter measures current in a circuit, not resistance. A voltmeter measures voltage and wouldn’t provide resistance information on its own. A multimeter can measure resistance when set to the ohms range, but the device specifically built for resistance measurements is the ohmmeter, making it the best choice here. Always ensure the circuit is fully de-energized and any stored charge is discharged before measuring.