Refraction and Lenses - Mission RL6 Detailed Help

When light moving through water reaches the boundary with air at an angle of incidence equal to the critical angle, the light ray will ____. List all that apply ... .

Click the button below to play an audio file.

Requirements for Total Internal Reflection (TIR):
Two requirements must be met for total internal reflection to occur. First, light must be in the more dense medium heading toward the boundary with the least dense medium. Second, light must be approaching the boundary with an angle of incidence that is greater than the value of the so-called critical angle.

Many beginning students of physics become quite confused by the concept of a critical angle and its relationship to total internal reflection. It is a commonly held wrong belief that TIR occurs when the incident angle is equal to the critical angle. But don't be fooled! The incident angle must be greater than the critical angle for total internal reflection to occur. When the incident angle is equal to or less than the critical angle, both reflection and refraction occur.

Definition of Critical Angle:
The critical angle is the largest angle of incidence for which refraction can occur for a particular boundary. When light is incident toward a boundary with a less dense medium at the critical angle, light refracts into the new medium with an angle of refraction of 90 degrees.