Angel Avitia ’s Reviews > Geometrical and Trigonometric Optics > Status Update

Fermat’s principle states that light rays of a given frequency traverse the path between two given points in the least amount of time. When two points in space are connected by a ray, the ray represents the shortest time path.
tT=nZ/c+n'Z'/c
OPL=ctT=nZ+n'Z'
nSinI=n'SinI'
Refraction is caused by the change in speed experienced by a ray/wave when it enters a different medium.
nSinIi=n'SinI=-nSinIr
Ei=Er+Et