Question
When a light ray travels from air into glass, which of the following statements is accurate after the light enters the glass?
  1. The ray bends away from the normal, and the speed decreases.
  2. The ray bends away from the normal, and the speed increases.
  3. The ray bends toward the normal, and the speed increases.
  4. The ray bends toward the normal, and the speed decreases.
Question by OpenStax is licensed under CC BY 4.0
Final Answer

(d)

Solution video

OpenStax College Physics for AP® Courses, Chapter 25, Problem 6 (Test Prep for AP® Courses)

OpenStax College Physics, Chapter 25, Problem 6 (AP) video thumbnail

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Video Transcript
This is College Physics Answers with Shaun Dychko. When a light ray travels from air into glass, it's going from a medium of index of refraction of approximately 1 to a medium with an index of refraction greater than 1 and it will refract towards the normal. So Θ r the angle of refraction is less than the angle of incidence in this case. So it's bending towards the normal so that narrows it down to options (c) and (d) and then the question is how about the speed? Well the index of refraction is an indication of speed because it's the ratio of the speed of light in a vacuum to the speed in the medium and so of course the speed can't be greater than (c)— this is the absolute maximum speed of anything— and this number when it's greater than 1, it means that v is less than c and the bigger this number is the less v must be since c is a constant. Okay! So the answer is (d): the ray bends towards the normal, and the speed decreases.