When a Beam of Light, Which Is Traveling in Glass

Multiple Choice

When a beam of light, which is traveling in glass, strikes an air boundary, there is

A) a 90° phase change in the reflected beam.
B) no phase change in the reflected beam.
C) a 180° phase change in the reflected beam.
D) a 60° phase change in the reflected beam.
E) a 45° phase change in the reflected beam.