Final answer:
The amplitude of an eddy current test indication depends on factors like the magnitude and direction of the induced eddy current and consequent magnetic damping, which are influenced by material properties and shape.
Step-by-step explanation:
The amplitude of the indication from a discontinuity during an eddy current test on the tubing is influenced by several factors. One primary factor is the magnitude and direction of the induced eddy current itself. As the moving conductor—such as a metal pendulum bob—passes through a magnetic field, eddy currents are generated, which in turn create magnetic fields that oppose the motion, thus causing magnetic damping. The amount of damping is affected by the metal's properties, its shape, and the strength of the magnetic field. For instance, objects with slotted metal demonstrate less effective eddy currents, which in turn produce less magnetic damping compared to solid metal objects.
In practice, these principles of eddy currents and magnetic damping have important applications in various areas, such as metal detectors, and braking systems in trains and roller coasters. In a metal detector, an eddy current induced in nearby metal changes the current within the secondary coil, resulting in a detection signal.