Total Internal Reflection

[b]Total Internal Reflection[/b] occurs when light bend so much away from the [b]normal[/b], when it [b]refracts[/b], that it ends up coming back and instead reflects off of the surface, back into the material. The light effectively gets trapped inside of the material. [b]In glass, Total Internal Reflection occurs at 42[degree][/b]. The point where it reflects internally (42[degree] for glass), is called the critical point. The light which goes towards the surface to exit the material is the [b]incidence ray[/b], the one that gets totally internally reflected. To work out the angle for Total Internal Reflection: [code] Critical Angle = [img src='https://res.cloudinary.com/deylrqt2d/image/upload/v1487981850/refractive_index_equations_2_azd5zg.svg'] [/code] [b]Note that this is calculating the critical angle when light goes from a more dense substance into a less dense one, the other way round will not work.[/b] Another way to look at it is to say that Total Internal Reflection occurs when the light refracts away from the normal, until it is 90[degree] or more. (Also note that before this critical angle, light is both refracted, and partially reflected, causing multiple [b]ghost[/b] images). [h3]Examples of Total Internal Reflection[/h3] [img style='width:100vw' src='https://res.cloudinary.com/deylrqt2d/image/upload/v1487982058/6479bfbbce38595157f4ff1cd0111190edacd806_cgcrdc.gif'] [img src='https://res.cloudinary.com/deylrqt2d/image/upload/v1487982058/refr-180dev-prism_dbegf6.jpg']