Eddy Current Testing (ET) Level I Practice Test

In eddy current testing, the coil’s response is governed by impedance—the total opposition to current flow in the coil. This combines both resistance (losses in the coil itself) and reactance (the inductive opposition that depends on frequency). The inductive part is important, but it’s only part of the picture; the coil also has resistance, so the overall impedance is what actually changes when eddy currents are induced in the nearby material. When a conductive piece or a flaw alters the eddy currents, it changes how much current the coil “sees,” shifting the impedance. That change in impedance is what testers monitor to detect defects or variations in material properties. Flux density describes the magnetic field itself, not how much the current is opposed to flowing, and back voltage is the induced emf from changing current—related concepts, but not the total opposition used for defect detection.