Unlike the virial theorem for particles, for the electromagnetic field the virial theorem is written as follows: E k f + 2 W f = 0 , where the energy E k f = ∫ ∫ A α α j α α − − g d x 1 d x 2 d x 3 considered as the kinetic field energy associated with four-current j α α , and W f = 1 4 μ μ 0 ∫ ∫ F α α β β F α α β β − − g d x 1 d x 2 d x 3 sets the potential field energy found through the components of the electromagnetic tensor.