N. 3 - 21 aprile 2001 - Giano Bifronte

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In the second case b), the standard Lorentz force is zero because,
according to SR, there are no fields outside the moving solenoid which
becomes also electrically polarized. However, the nonstandard
expression, which in a nonrelativistic formulation does not foresee
electric polarization, predicts an impulse
∫ fdt = -QAm ,
in the direction of v , of the same order of magnitude of that due to the
force QEm . Here, a non-null result favors the nonrelativistic
interpretation.
4 - Test of the fields produced by an open current
As mentioned in the Introduction, all the existing tests of the fields
produced by moving charges refer to charges moving in closed circuits
(closed currents). The magnetic field produced by an isolated moving
charge (open current) has never been tested.
If a charge is placed in the laboratory reference frame it produces a
static electric field in that frame. According to relativity a frame moving
with respect to the laboratory will experience also a magnetic field. In
fact, for relativity the moving charge forms a current and the charge and
current density transform as a four-vector. Thus, by Maxwell's
equations the current generates a magnetic field even though there is
only an electric field in the rest frame of the charge. In a nonrelativistic
interpretation of electrodynamics, a current may be defined as due to
charges moving in a closed circuit. Isolated charges may not form a true
current even if they move with respect to some observer (open current).
To many physicists the idea that open currents are not true currents
generating a magnetic field may seem to be untenable. However, we
recall that the physical behavior of charges moving in a closed circuit is
quite different than that of open currents. For example, the correct (for
relativity) expression of the force on a magnetic dipole has to take into
account the fact that the moving charges forming the dipole current are
linked to the closed loop forming the dipole m . There are internal
stresses contributing to the correct force on m that do not exist for open
currents. Thus it is not unreasonable to think that the forces acting on,
or the fields generated by, open currents may differ from those due to
closed currents. Furthermore, the motion of charges in a closed circuit is
a kind of absolute motion (with respect to the frame at rest with the