Relativistic Electrodynamics revealed that the Lorentz-Formula for electromagnetic induction E = v X B - pertaining to the electric field strength E acting on a charge crossing a magnetic field B with relative velocity v - can be deduced from the more fundamental laws of Special Relativity.

Imagine a grounded stationary superconducting circuit carrying dc-current I with a straight wire section and an observer moving with velocity v parallel to that wire. This observer will simultaneously notice the magnetic field B surrounding the wire (which also exists in the laboratory rest frame) and an electrostatic field E= v X B inexistent in the laboratory rest frame, apparently emerging from that wire. However, the source of this electro*static field is not deducible from the Lorentz-Formula. Moreover, Maxwells field equations require that an electrostatic field E can only emerge from charges acting as sources of electrostatic flux. Hence also the electric field E = v X B must emerge from electrostatic charges located in the wire. With respect to the conservation of charge rule the required charging of the previously electrically neutral wire can only result from a disparity among the charge-densities of negative electrons and stationa*ry positive atomic nuclei in the wire. This apparent charge disparity has been shown to be a pure relativistic effect which may be called Differential Lorentz Contraction referring to the different variation of densities of the drifting conduction electrons and the statio*nary atomic nuclei, when observed from a moving frame of reference. Essentially, the charge-disparity in the wire is proportional to the current I and the relative velocity v of the observer. (The precise derivation of this charge disparity can be extracted from textbooks dealing with Special Relativity or Relativistic Electrodynamics. (See e.g. R. Feynman Lectures on Physics 2, Ch. 13-6.) The most comprehensive analysis is based on relativistic 4-potential and 4-current vector transformations.

With reference to the above observations the following 3 thought-experiments and questions can be formulated :

a) a) If the moving observer lets a small piece of (otherwise isolated) metal slide over the wire: Will that sliding piece of metal acquire the same (apparent) electrostatic potential as the wire and become electrostatically charged?

b) b) If the moving piece of metal is detached from the wire without change of velocity: Will that piece of metal retain the a.m. charge if it remains electrically isolated?

c) c) If that piece of metal is decelerated and stopped to rest in the laboratory frame: Will it conserve its a.m. charge?

Remark 1:

Electric charge is a relativistically invariant quantity being conserved during any acceleration or deceleration process. Hence it can be expected that if the first answer is yes, all further answers should also be yes.

Remark 2:

The a.m. piece of metal also is subjected to homopolar induction, which however only superimposes an electric dipole moment without affecting its total charge.