Total Internal Refraction
At the border of two materials usually both reflection and refraction appears
In some peculiar situations however the refracted light is also reflected! --> reflection is total!
This can happen when light travels from a medium with bigger index of refraction to one with a smaller index of refraction, and the incident angle is big enough
for high enough ?1= ?0 --> ?2=900
if ?1> ?0 :no refracted ray --> total reflection