Some remarkable charge–current configurations

Abstract

We investigate how different magnetization distributions interact with an external electromagnetic field. Strong selectivity to the time dependence of the external electromagnetic field arises for particular magnetizations and suggests that it can be used for practical applications. We review the properties of the known charge–current radiationless configurations. The radiation field of toroidal-like time-dependent current configurations is investigated. Infinitesimal time-dependent configurations are found outside which the electromagnetic field strengths disappear but the potentials survive. For a number of time dependences, their finite radiationless counterparts can be found. In these cases topologically nontrivial (unremovable by a gauge transformation) electromagnetic potentials exist outside the sources. The well-defined rule obtained for constructing time-dependent infinitesimal sources suggests the existence of finite nontrivial radiationless sources with a rather arbitrary time dependence. The latter can be used to carry out time-dependent Aharonov–Bohm-like experiments. Examples are given of nonstatic current configurations generating the static electric field and adequately described by the electric vector potential rather than by the scalar one.