  This paper uses an alternative approach to study the monochromatic plane wave
propagation within dielectric and conductor linear media of
plane-parallel-faces. This approach introduces the time-averaged Poynting
vector modulus as field variable. The conceptual implications of this formalism
are that the nonequivalence between the time-averaged Poynting vector and the
squared-field amplitude modulus is naturally manifested as a consequence of
interface effects. Also, two practical implications are considered: first, the
exact transmittance is compared with that given by the Beer's Law, employed
commonly in experiments. The departure among them can be significative for
certain material parameter values. Second, when the exact reflectance is
studied for negative permittivity slabs, it is show that the high reflectance
can be diminished if a small amount of absorption is present.
