What measurement tool is typically used to check the voltage across the terminals of a motor?

The correct choice is the voltmeter, which is specifically designed to measure the electrical potential difference, or voltage, across two points in an electrical circuit. When checking the voltage across the terminals of a motor, a voltmeter is connected in parallel with the terminals to obtain an accurate reading of the voltage supplied to the motor. This measurement is crucial for diagnosing motor performance and ensuring that it operates within the specified voltage range.

Regarding the other tools mentioned, an amperemeter measures the current flowing through a circuit, while an ohmmeter assesses resistance within a circuit. A frequency meter is used to measure the frequency of alternating current. Therefore, while these other instruments are essential for different measurements in electrical work, none of them fulfill the purpose of measuring voltage across motor terminals like a voltmeter does.