Vector potential, electromagnetic induction and "physical meaning"

TL;DR

This paper revisits Blondel's 1914 experiment to argue that the vector potential, not magnetic flux variation, is the true physical agent behind electromagnetic induction, emphasizing the importance of gauge choices and theoretical interpretation.

Contribution

It clarifies the physical significance of the vector potential and challenges the conventional flux-based explanation of electromagnetic induction.

Findings

The vector potential is the physical agent in electromagnetic induction.

The Lorenz gauge provides the physically meaningful potentials.

Gauge transformations do not alter the physical fields but affect the interpretation.

Abstract

A forgotten experiment by Andr\'e Blondel (1914) proves, as held on the basis of theoretical arguments in a previous paper, that the time variation of the magnetic flux is not the cause of the induced $emf$: the physical agent is instead the vector potential through the term $-\partial\vec A/\partial t$ (when the induced circuit is at rest). The "good electromagnetic potentials" are determined by the Lorenz condition and retarded formulas. Other pairs of potentials derived through appropriate gauge functions are only mathematical devices for calculating the fields: they are not physically related to the sources. The physical meaning of a theoretical term relies, primarily, on theoretical grounds: a theoretical term has physical meaning if it cannot be withdrawn without reducing the predictive power of a theory or, in a weaker sense, if it cannot be withdrawn without reducing the descriptive proficiency of a theory.