Light enters the smooth,flat surface of a block of glass from the vacuum of space (e.g.,a spacecraft window).What is the speed of light inside the glass compared with that in a vacuum?
A) The speed will depend on the angle that the light ray makes with the perpendicular to the surface, becoming slower as the angle increases.
B) The speed will be the same because the speed of light is always constant, by definition.
C) The speed will be faster because the glass is denser than the vacuum.
D) The speed will be slower because the glass is denser than the vacuum.

Question

Quizplus · Accepted Answer

The speed of light inside the glass will be slower than the speed of light in a vacuum because the glass is denser than the vacuum. This decrease in speed is due to the optical properties of the glass and is known as the refractive index. The refractive index varies with wavelength, so the speed of light in the glass will also vary slightly depending on the color or wavelength of the light. However, in general, the speed of light in glass is about two-thirds of the speed of light in a vacuum.

Light Enters the Smooth,flat Surface of a Block of Glass