What forms the basis of the signal that locators respond to?

• A. A static electric field
• B. A thermal gradient
• C. An electromagnetic field created by alternating current in the conductor
• D. A radio signal

Answer: (C)

Locators pick up the electromagnetic field that surrounds a buried conductor when current flows through it. When the line carries alternating current, this field changes over time, creating a signal the receiver’s coil can detect. That changing electromagnetic field is what lets you locate and trace the line underground. A static electric field wouldn’t provide the time-varying signal the instrument needs, a thermal gradient isn’t involved in locating, and while other systems can use different signals, the fundamental basis here is the electromagnetic field generated by the conductor’s alternating current.