What device is commonly used to measure electromotive force?

The device that is commonly used to measure electromotive force is the voltmeter. Electromotive force (EMF) refers to the voltage generated by a source like a battery or generator when no current is flowing in the circuit, essentially representing the potential difference. A voltmeter is specifically designed to measure this potential difference across two points in an electrical circuit.

When connected across a voltage source, the voltmeter provides a reading that indicates the amount of EMF present. It operates under the principle of having high internal resistance to prevent it from drawing significant current away from the circuit, thus allowing an accurate measurement of the voltage.

In contrast, an ammeter is used to measure electric current, an ohmmeter measures resistance, and a barometer measures atmospheric pressure. These devices serve different purposes and cannot measure voltage or EMF, which reinforces the importance of a voltmeter in measuring electromotive force accurately.