QUESTION #337

# The index of refraction for liquid water is 1.33. What is the index of refraction for ice? The physical density is changed, but is the optical density changed as well?

The index of refraction for ice is 1.31.

The index of refraction of a material is the ratio of the velocity of light in a vacuum to that in the material.

Meaning,

n = c/v

where 'n' is the index of refraction value of a material, 'c' is the speed of light in a vacuum, and 'v' is the speed of light in a material.

The net velocity of light in a material is decreased because of continual absorption and reemission of the light wave by atoms that it encounters. The light wave energy absorbed sets electrons in the atoms into vibrational motion. This energy is then reemitted as an electromagnetic wave with the same frequency of the original wave.

The index of refraction usually increases as the physical density of the material increases.

The optical density of a material relates to the sluggish tendency of the atoms of a material to maintain the absorbed energy of an electromagnetic wave in the form of vibrating electrons before reemitting it as a new electromagnetic wave. The more optically dense a material is, the slower light will move through the material.

To answer your question, the optical density of ice is less than that of water. Light travels through ice faster than it travels through water.