Which of the following is used to assess the voltage of a structure relative to surrounding soil?

The voltmeter is specifically designed to measure the electric potential difference, or voltage, between two points in an electrical circuit. In the context of assessing the voltage of a structure relative to the surrounding soil, a voltmeter can be used to check for stray voltage or potential differences that might affect the integrity of the structure or the safety of personnel.

By connecting the voltmeter's probes to the structure and the ground, you can determine the voltage level present which can be critical for evaluating corrosion potential in cathodic protection systems. Understanding this voltage helps in assessing the effectiveness of the cathodic protection measures implemented on metal structures to mitigate corrosion.

Other options, while related to electrical measurements, are not suited for measuring voltage in this specific context. An ammeter is used for measuring current, a galvanometer detects small currents and is not typically used for voltage measurements, and a multimeter, while versatile and capable of measuring voltage, current, and resistance, is not as specialized for directly assessing the voltage of a structure against surrounding soil as a voltmeter would be.