1) There, to see. The laws of reflection and refraction have been correctly enunciated at the preceding level, with beautiful gif in the F part. For a priori, eventually a link to this specific page of the lower level (hill). And as a result, in N-1 we will call the level still lower (flat).
2) On the other hand, it is perhaps time to reveal more about the inadequacies of geometric optics. Hill level, we said that light was transmitted through a dioptre according to the law of Snell-Descartes, and reflected upon a mirror. In fact, even on a dioptre, one part of the energy is eflected and the other is refracted. Even limited to the visible, we see that this distribution of energy depends on incidence angles (make look at the glass of a window, see through and see inside, make vary the angle of view relative to the normal for the crystal). It is important because this brings the parasitic images (Ghosts), and the antireflective layers of the correcting vessels or lens lenses for example. It is at this level we have to talk about this. But it is a link to the wave optics (rather part M of the course)
