Which factor is essential for generating eddy currents in a conducting specimen?

The essential factor for generating eddy currents in a conducting specimen is the presence of conductive materials. Eddy currents are loops of electrical current that are induced within conductors by a changing magnetic field due to electromagnetic induction. For eddy currents to be generated, the material must be capable of conducting electricity, allowing the changing magnetic field to induce circular currents within it.

While the presence of an external magnetic field and high-frequency alternating current do play roles in the process, it is the conductivity of the specimen itself that enables those currents to flow. Without conductive materials, there would be no means for the eddy currents to circulate, making this characteristic the fundamental requirement for their generation.