An interesting, useful and low-cost oscillator has been presented. It is a spring–magnet system
whosemotion isweakly coupled to a nearby non-magnetizable conductive plate by the Foucault
(eddy) currents induced in the plate that set a dragging on the magnet. This oscillating
magneto-mechanical system can be easily set up with parts and materials readily available
in an introductory physics teaching laboratory. A single piece of equipment, a digital-storage
oscilloscope, is required to do the experiments described above. This system is an example
of a damped harmonic oscillator and its oscillation parameters can be set without difficulty.
It may be seen in figure 6 that our experimental curve agrees with the theoretical curve. They
depart slightly when the distance b becomes small (less than 10 mm), i.e. when the magnet
naturally rests in equilibrium quite near the metallic plate at the start. This small departure can
be explained by the failure of the single-dipole approximation we assumed at the beginning
of section 2 for such small distance. However, using a higher order approximation for the
magnetic field means a set of rather lengthy and cumbersome relations, and the gain in
accuracy would be not that much; therefore we stood by the simpler dipole approximation that
has given us acceptable agreement with the experimental data we took. We have shown both
theoretically and experimentally that this simple system can be applied to measure both the
electrical conductance and the thickness of a conductive plate with good accuracy (error∼2%).
We found that 1% error in measuring the distance b leads to a ∼3% error in the value of the
plate conductivity.
This magneto-mechanical system lends itself to further investigations with simple minor
modifications, for instance by boring an orifice in the plate one can allowthe magnet to oscillate
up-and-down through the plate (this work is now completed and will be published elsewhere).
Finally, the magneto-mechanical system presented here is an excellent experiment for senior
undergraduate physics and engineering laboratories, as well as for classroom demonstrations.
The level of readership is therefore from undergraduate to graduate students, as well as for
any university teaching physicist.