Final answer:
Total internal reflection occurs when light hits the boundary between two media at an angle greater than the critical angle, and it is completely reflected back into the medium with the higher index of refraction.
Step-by-step explanation:
When light passes from a medium with a higher index of refraction to a medium with a lower index of refraction at an angle greater than the critical angle, a phenomenon called total internal reflection occurs. This condition means that none of the light escapes into the second medium; instead, all of it is reflected back into the first medium. The condition is defined by having an incident angle greater than the critical angle, which is the angle of incidence that results in an angle of refraction of 90°. For total internal reflection to take place, the index of refraction in the second medium must be less than that of the first. When light reflects during total internal reflection from a medium with a higher index of refraction, a 180° phase change, or a λ/2 shift, occurs, affecting the wave characteristics of the light.