what is total internal reflection, and how is it related to the critical angle?
The minimum angle at which total internal reflection occurs is known as the critical angle (for Perspex this is about 43Ë). At any angle greater than the critical angle, total internal reflection occurs and the light ray obeys the normal rules for reflection (i.e. angle of incidence = angle of reflection). 1  Page. 2  1. 3  2.
Total Internal Reflection and the Critical Angle. If a ray of light is leaving a denser medium, it will bend away from the normal. As can be seen from the above diagram, as the angle of incidence inside the material increases the angle of refraction increases to a point at which it leaves the material at 90Ë.