Which instrument is used to measure electrical resistance?

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

Answer: (D)

Measuring resistance relies on an instrument that applies a known stimulus and reads the response to compute R. An ohmmeter is designed for this purpose: it supplies a small current through the unknown resistance (usually from an internal battery) and measures the resulting voltage drop, or it measures current and uses Ohm’s law to display the resistance directly in ohms. This direct reading is what makes the ohmmeter the correct tool for determining resistance.

A voltmeter, by contrast, is meant to measure voltage across two points and is not calibrated to give resistance by itself. An ammeter measures current in a circuit, not resistance. A galvanometer detects small currents and is a sensitive component used in some meters, but it isn’t used alone to measure resistance.