Minimizing postulation in a senior undergraduate course in   electromagnetism
  An approach to the teaching of electromagnetism to senior undergraduate students, designed for overcoming the fragmentation of the theory is described. As usual it starts from the static case, but it is strictly based on Helmholtz theorem of uniqueness of vector fields, on primary experimental observations upon the sources of electric and magnetic fields, on Lenz's law and on principles of superposition and reciprocity of interactions. Thereafter, without further postulation, all laws and rules arise in a procedure where electricity and magnetism parallel one another. Maxwell's equations are built up on a step-by-step basis, showing that electromagnetic field can be considered but a twofold linear vector field obeying the simplest principles of physical theories. It is shown that every system of units fits this formalism, provided suitable values are assigned to some constants arising therein from superposition principle. 
Nelson P. Andion