Total Internal Reflection Summary
The maximum angle of refraction is 90°
The incident angle at which this occurs is called the critical angle.
At and beyond the critical angle no refraction happens, just internal reflection.
The critical angle for glass is around 42°.
Total internal reflection is used in optical fibres to transmit pulses of light.
Optical fibres can carry much more information than copper wires.
Periscopes use total internal reflection to look over things.
Binoculars use total internal reflection to shorten their length.