Which instrument is used to measure the voltage across a component?

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

Answer: (C)

To measure the voltage across a component, you use a voltmeter. A voltmeter is connected across the two points of interest, effectively in parallel with the component, so it reads the potential difference between them without forcing current through the element. Its high internal resistance minimizes loading the circuit, which keeps the voltage reading accurate. By contrast, an ammeter is meant to measure current and is placed in series, which would alter the circuit if used to "read" voltage. An ohmmeter measures resistance by applying a small current and observing the response, not the voltage across a component. A wattmeter gauges power, typically requiring both voltage and current. So, for directly reading the voltage across a component, the voltmeter is the appropriate instrument.