What does the refractive index (n) measure?

The refractive index (n) is defined as the ratio of the speed of light in a vacuum to the speed of light in a specific material. This fundamental concept in optics highlights how light behaves as it travels through different media. When light enters a medium with a different refractive index, its speed changes, which in turn causes a change in direction, a phenomenon known as refraction.

The refractive index can be expressed mathematically as:

n = c / v

where "c" is the speed of light in a vacuum, and "v" is the speed of light in the material. A higher refractive index indicates that light travels slower in that medium compared to its speed in a vacuum, which has significant implications for optical applications, including lens design, fiber optics, and various imaging technologies.

Other options do not correctly describe what the refractive index measures. The speed of sound is unrelated to optics; the density of a material does not directly correlate with how light propagates; and the absorption rate pertains to how much light is absorbed rather than its refractive behavior.