Non-Destructive Testing (NDT) Practice Test

The principle of eddy current testing mainly relies on which physical concept?

1. Static electricity

2. Magnetism

3. Thermal conductivity

4. Electromagnetic induction

The correct answer is: Electromagnetic induction

The principle of eddy current testing is fundamentally based on electromagnetic induction. This concept involves the generation of electric currents, known as eddy currents, within a conductor when it is exposed to a changing magnetic field. When an alternating current flows through a coil, it creates a time-varying magnetic field around it. If a conductive material is placed within this magnetic field, the changing magnetic lines induce circular currents in the material, which are the eddy currents. These eddy currents produce their own magnetic fields, which can affect the original magnetic field and lead to measurable changes in impedance of the coil. By analyzing these changes, inspectors can assess various properties of the material, including its electrical conductivity, thickness, and even the presence of flaws or cracks. The other options do not correlate with the operating principles of eddy current testing: static electricity refers to stationary electric charge, magnetism is a broader term that doesn’t specifically encompass the induction process as utilized in this testing method, and thermal conductivity relates to the ability of a material to conduct heat, which is not a factor in the electromagnetic processes decisive for eddy current testing.