If you want to measure electrical pressure in a circuit, which device would you use?

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

Answer: (D)

Electrical pressure is voltage, the potential difference between two points in a circuit. A voltmeter is used to measure that voltage, so it’s connected across the points where you want to know the pressure. Because it has very high input resistance, it draws almost no current and doesn’t disturb the circuit while you measure.

The other devices measure different things: an ammeter measures current and is placed in series in the path of the circuit; an ohmmeter measures resistance and is used on components or circuits that are powered off; a thermometer measures temperature. So for measuring electrical pressure, the voltmeter is the best choice.