  An electromagnetic analysis is presented for experiments with strong
permanent disc magnets. The analysis is based on the well known experiment that
demonstrates the effect of circulating eddy currents by dropping a strong
magnet through a vertically placed metal cylinder and observing how the magnet
is slowly falling through the cylinder with a constant velocity. This
experiment is quite spectacular with a super strong neodymium magnet and a
thick metal cylinder made of copper or aluminum. A rigorous theory for this
experiment is provided based on the quasi-static approximation of the Maxwell
equations, an infinitely long cylinder (no edge effects) and a homogeneous
magnetization of the disc magnet. The results are useful for teachers and
students in electromagnetics who wish to obtain a deeper insight into the
analysis and experiments regarding this phenomenon, or with industrial
applications such as the grading and calibration of strong permanent magnets or
with measurements of the conductivity of various metals, etc. Several
experiments and numerical computations are included to validate and to
illustrate the theory.
