The mechanism of electromigration is discussed from the perspective of electromagnetism, rather than from the traditional view of momentum exchange owing to collisions between electrons and diffusing ions. It is suggested that, from the perspective of conservation of momentum, the momentum transferred to the diffusing ions is related to the Maxwell stress, and the effective charge is proportional to the density of the net charge within the volume element. It is also suggested that, from Poynting’s theorem, the energy associated with electromigration is related to the work done by the electric field, and the conversion of the nonelectrostatic energy from the electric power source into the chemical energy of the diffusion system. From both perspectives, the effective driving force can be shown to have a square dependence on the current density. Therefore, it is suggested that the effective charge number is linearly related to the current density.