Geometrical optics describes light propagation using wavefronts and rays. Wavefronts are surfaces passing through points of a wave that have the same phase and amplitude. Rays describe the direction of wave propagation as a vector perpendicular to the wavefront.

1. Geometrical Optics
In describing the propagation
of light as a wave we need to
understand:
wavefronts: a surface passing
through points of a wave that
have the same phase and
amplitude.
rays: a ray describes the
direction of wave propagation.
A ray is a vector perpendicular
to the wavefront.