Non-Destructive Testing (NDT) Practice Test

Which of the following does NOT describe eddy currents?

1. They are induced by a static magnetic field

2. They can create heat within conductive materials

3. They flow in closed loops

4. They are affected by the conductivity of the material

The correct answer is: They are induced by a static magnetic field

The concept of eddy currents is fundamentally linked to the principles of electromagnetism. Eddy currents are created when a changing magnetic field induces electrical currents within a conductor, not by a static magnetic field. When a conductor is exposed to a changing magnetic field, the variation in the magnetic field causes the electrons in the conductive material to move, resulting in circular paths, or "eddy currents." This phenomenon is governed by Faraday's Law of Electromagnetic Induction. In addition, eddy currents have practical implications, such as generating heat due to the resistivity of the material they flow through. This heat can be beneficial in applications like induction heating but can also lead to losses in efficiency in certain contexts. Moreover, the strength and behavior of these currents are indeed significantly affected by the electrical conductivity of the material through which they flow, as higher conductivity allows eddy currents to circulate more freely. Given this understanding, "They are induced by a static magnetic field" is not a correct characterization of eddy currents, as it misrepresents the fundamental principle driving their generation.