Novel, first-principles approach to deriving Electromagnetic field transformations under oblique Lorentz-Boosts and arbitrary Spatial Rotations

The standard classic special relativistic transformation of the electromagnetic (EM) field under proper Lorentz transformations is revisited. As to the pure Lorentz-boosts, popular treatments on EM transformation contemplate ideal geometries generating special static charge and steady current distributions and in conjunction, invoke parallel and perpendicular (to the boost-velocity) components of the fields so engendered; the outcomes subsequently being suitably generalized. We demonstrate ab initio, the EM field transformation under arbitrary oblique uniform relative boost velocities from a broader, rigorous yet remarkably lucid perspective, exploiting the antisymmetry of the EM-field tensor and symmetry of the general Lorentz-boost transformation preemptively eliminating the labor of performing complicated matrix multiplications. Gratifyingly, this instructive exercise manifestly encompasses time varying fields and yields the transformation relations in a coordinate-free form. Further, the EM field transformation under proper, instantaneous 3D rotations is demonstrated to transform as a passive rotation of the coordinate axes, where the electric and magnetic fields transform independently as purely electric and magnetic fields, respectively. The present didactical exercise, amenable to be incorporated in graduate courses on relativistic electrodynamics, should serve as an excellent illustration on how powerful symmetry arguments simplify the otherwise tedious calculations while endowing complete generality to the connections obtained.

Salil K Bedkihal, Rajeev K Pathak · 2021