Light enters a plane-parallel block of glass from the vacuum of space and leaves again into space through the opposite side (e.g.,in a space-borne instrument).What is the speed of light after it leaves the glass?
A) It is the same speed it was before it entered the glass.
B) The exit speed will depend on the thickness of the glass, becoming slower the thicker the glass.
C) It is faster than when it entered because it has passed through the dense glass.
D) It is slower because it has passed through the glass and been slowed by it.

Question

Quizplus · Accepted Answer

The speed of light in a vacuum is constant and does not change after passing through a medium like glass. Once it exits the glass and re-enters the vacuum, it returns to its original speed, which is the speed of light in a vacuum.

Light Enters a Plane-Parallel Block of Glass from the Vacuum