What is the Index of Refraction?
Light moves at its maximum possible velocity in the absence of matter. For example, in space light travels approximately 186,000 miles per second. But the presence of matter slows light down; or more specifically, the forces which bind atoms slow light down. The Index of Refraction for any substance is the ratio of the velocity of light in a vacuum to its velocity in a given substance. The higher the index, the slower the velocity. Thus, if we say that a particular crystal has an index of refraction of 2.000 we mean that light would pass through a vacuum at twice the velocity that it can go through that crystal. Why do different substances have different refractive indices? As previously pointed out, the velocity of light through any material is retarded by forces binding its atoms and molecules. Therefore, the degree to which a particular beam of light is slowed depends both upon the types of atoms present (the chemical composition) and the nature of the arrangement of those atoms. Fo
