show that electromagnetic waves in a vacuum are transversal waves. transversal waves mean that the electric and magnetic wave fields are always perpendicular to each other and to the direction of the wave propogation... but how does this link to a vacuum? and how can you show that a field is perpendicular? consider an electromagnetic plane wave and assume that it hits a boundary of a medium under a certain angle. assume that the dielectric constant, and magnetic permeability of the medium are given. what are the boundary conditions on the electric and magentic fields at the boundary of the medium? are there solutions for the plane waves that come in perpendicular to the boundary? (find them) a plane wave is a wave travelling in the x-direction and has no y- or z- dependence. hitting a medium under a certain angle= a case of oblique incidence? if the symbols were easier to type, i would write my answer, but to make sure, there are 4 boundary conditions for the case of it being parallel, in which #1 and #4 reduce to one common one and the third boundary condition also reduces. for the case of it being perpendicular, it should have some connection with being parallel, but what? i assume that since the electric and magnetic fields are already perpendicular to one another, that there will only be two boundary conditions because not both the electric and the magnetic field can be perpendicular to this medium... suppose that the medium would also contain a constant density of free electrons that respond to electric fields according to Ohm's law, describe the effect of the conduction electrons on the wave. putting a free charge on a conductor makes it flow out to the edges. magnetic fields in a conductor lag behind the electric field, thus energy is not equally shared between the electric and magnetic fields. HELP!