New formulation of the laws of reflection of light

摘要

A new formulation of the laws of reflection of light based on the particle model is presented, and it is shown the equivalence between the new and the classic formulations. The proposed formulation has a significant educational value, as it allows drawing analogies between the phenomena of light reflection and elastic collisions, which are very well known by students. The proposed formulation is: "If at one point on a surface whose orientation in space is defined by a unit vector k, strikes an incident ray corresponding to a plane wave (propagating through a homogeneous and isotropic medium) whose direction of propagation coincides with that from a unit vector u_i [expressed in terms of its components with respect to an orthonormal coordinate system, with one of its axis coinciding with the direction of k (u_i = u_(ix) i + u_(iy) j + u_(iz) k)], it will be reflected so that the unit vector whose direction coincides with that from the reflected ray, u_r, will only differ from the unit vector whose direction coincides with that from the incident ray, in the change of the sign of the component in the direction of k (u_i = u_(ix) i + u_(iy) j -u_(iz) k )". Stated in everyday language, is equivalent of saying that the reflection of light occurs as if the photons underwent perfectly elastic collisions with the surface in question. As an example, this formulation is applied for the resolution of the classic reflection problem of the three plane mirrors forming a trirectangular trihedron.