Which instrument is used to measure resistance?

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

Answer: (C)

Measuring resistance requires a device that can apply a known current to a component and sense the resulting response so the resistance can be read. An ohmmeter is built for this purpose. It contains a small internal battery and a meter; when you connect it across a component with the power off, the meter pushes a known current through the component and either directly displays the resistance or enables a calculation from the measured current and voltage. This is different from other meters: an ammeter measures current by being placed in series in a circuit, a voltmeter measures voltage by being placed in parallel, and a wattmeter measures power by combining current and voltage (and sometimes phase information). So for resistance, the appropriate instrument is the ohmmeter.