Specifically, suppose that one has a current density formula_1 that produces an electric field formula_2 and a magnetic field formula_3, where all three are periodic functions of time with angular frequency ω, and in particular they have time-dependence formula_4. Suppose that we similarly have a second current formula_5 at the same frequency ω which (by itself) produces fields formula_6 and formula_7. The Lorentz reciprocity theorem then states, under certain simple conditions on the materials of the medium described below, that for an arbitrary surface "S" enclosing a volume "V":