How do eddy currents levitate objects in the jumping ring and floating tube experiments?

[chanderjeet]

Can someone explain the role of eddy currents that produce levitation such as in the floating tube expt or the jumping ring? How is the jumping ring altered to achieve stability? i.e raising the ring a fixed distance above the coil? Like in maglev transportation...or is it just dependent on the strength of the magnetic field?

 

[Bob S]

You have not given us a fuller description of the eddy current "jumping ring" or "floating tube", but based on my experience with eddy currents, the force comes about because of the inducing magnetic field B interacting with currents produced by the inducing dB/dt in conductors. The force is in a direction to push the conductor (conducting loop) to a region of lower B and dB/dt. This is (was) the basis for the popular repulsion-start single-phase electrical motors manufactured up until about WW II.

I have seen sheets of aluminum in 500-Hz oscillating vertical magnetic fields (+/- 2000 Gauss) align along the field lines to minimize the energy loss (heat dissipation).
Bob S