What instrument is used to measure voltage?

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

Answer: (D)

A voltmeter is used to measure voltage because it is designed to measure the potential difference between two points. It has a very high internal resistance, so it draws only a tiny current and does not significantly affect the circuit—this is why it’s connected in parallel across the component or points where the voltage is to be measured.

In contrast, an ammeter measures current and is placed in series with the circuit, since current is the same through elements in a series path, and ammeters have low resistance to avoid dropping voltage. A galvanometer is a sensitive current-detecting device (the moving-coil element inside many meters); without additional components it mainly measures small currents, though it can be configured for different ranges. An ohmmeter measures resistance and uses its own internal source, so it’s used only when the circuit is de-energized to determine how much resistance a component has.