When light travels from an optically denser medium to a rarer medium at the interface, it is partly reflected back into the same medium and partly refracted to the second medium. This reflection is called the internal reflection.
Total Internal Reflection (TIR) is the phenomenon of complete reflection of light back into the same medium for angles of incidence greater than the critical angle of that medium.
Conditions for TIR:
1.The incident ray must be in optically denser medium.
2. The angle of incidence in the denser medium must be greater than the critical angle for the pair of media in contact.
