Say you have a superconducting loop of copper. If there's an increasing magnetic field through it that induces an E field around the loop, how are the electrons moving when the field stops increasing? As I understand it the current is preserved. Is there some way to calculate the energy possessed by the electrons using the magnetic energy density? Could we take it a step further and calculate the speed that the electrons are moving by the kinetic energy equation? I suspect this a quantum mechanical problem that transcends the classical picture of electrons moving.