Eddy current testing operates based on which fundamental principle?

Eddy current testing operates based on the principle of electromagnetic induction. This principle states that a changing magnetic field within a conductor induces electric currents, known as eddy currents, within that conductor. When an alternating current flows through an examination coil, it creates a varying magnetic field. As this magnetic field penetrates the conductive material being tested, it induces eddy currents. These currents flow in circular paths within the material.

The key aspect of this method is that the characteristics of the induced eddy currents can be influenced by the properties of the material, such as conductivity, permeability, and the presence of discontinuities like cracks or corrosion. By analyzing the changes in the eddy currents, operators can assess the integrity and structural characteristics of the material without physical contact or damage.

The other options listed, while related to electromagnetic phenomena, do not directly pertain to the principle by which eddy current testing operates, as they are concepts that describe different processes in electromagnetism and material behavior.