Which instrument would you use to measure electric potential?

The tool used to measure electric potential is a voltmeter. A voltmeter is specifically designed to measure the voltage difference between two points in an electrical circuit. It is connected in parallel with the circuit component across which you want to measure the potential difference.

The operation of a voltmeter typically involves high internal resistance, which minimizes the effect of its connection on the circuit being measured. This allows for accurate readings without significantly altering the circuit's behavior.

In contrast, the other instruments have different functions: an ammeter measures current, a wavemeter is used to measure the frequency or wavelength of radio waves, and an ohmmeter is used to measure resistance in a circuit. None of these devices serve the purpose of directly measuring electric potential like a voltmeter does.