ABSTRACT
The study of propagation of light in geometric optics includes the concept of rays and wavefronts. A ray, a mathematical abstraction, is considered to be a line perpendicular to the wavefront, and can essentially be thought of as a thin pencil of light. A ray can be thought of as a propagation of energy in the limit of wavelength going to zero. Fermat's principle enunciated by Pierre de Fermat can be used to determine the path of light rays. Light rays travel in straight lines in a homogeneous isotropic medium since the optical path connecting any two points in such a medium is minimum only for a straight line. This simple principle can be used to derive the laws of reflection and refraction. The chapter derives Snell's law of refraction using Fermat's principle. This law of refraction is considered to be the fundamental law of geometric optics.
