#406Total Internal Reflection Tank

A single ray is injected into a glass tank and marched wall to wall, reflecting specularly at each face. At every bounce its incidence angle is tested against the critical angle θc = asin(1/n): beyond it the wall reflects totally and the beam races on undimmed, below it a slice of light leaks out and the trapped ray fades — so the zigzag lives or dies on the geometry. Three slightly dispersed wavelengths are marched separately, fanning the path into a chromatic ribbon over the water tint. Scroll to change the refractive index (and with it the critical angle); hover to aim the entry beam.