Suppose a ray of light traveling in a material with an index of refraction n a reaches an interface with a material having an index of refraction n b . Which of the following statements must be true for total internal reflection to occur?

Check all that apply. A. The angle of incidence must be less than the critical angle. B. na = nbC. na > nbD. The angle of incidence must be greater than the critical angle. E. The angle of incidence must be equal to the critical angle.

C and D

Explanation: One of the first rule for total internal reflection to occur is that the ray must move from a dense to a less dense medium, hence refractive index of medium a must be greater than that of b.

When a ray moves from a dense to a less dense medium, the refracted ray moves away from the normal thus increasing the size of the angle of refraction (total internal refraction occurs when the angle of refraction is 90° and the angle of incidence at this point is known as the critical angle), hence the angle of incidence must be greater than the critical angle.

These points verifies option C and D