What does the index of refraction measure?

The index of refraction is a fundamental property of materials that quantifies how much light slows down and bends, or refracts, when it passes from one medium to another. This bending of light occurs due to a change in speed as light enters a new medium, which can be quantified using the index of refraction. Mathematically, the index of refraction (n) is defined as the ratio of the speed of light in a vacuum to the speed of light in the material. A higher index indicates that light travels slower in that medium relative to vacuum, resulting in greater bending when light transitions between two different media.

Understanding the index of refraction is crucial in optics, as it determines how lenses and other optical components focus and manipulate light. This property is also why phenomena like total internal reflection occur, allowing technologies such as fiber optics to function effectively.