What does the refractive index measure?

The refractive index is a measure of how much light slows down as it passes through a medium compared to its speed in a vacuum. It is defined as the ratio of the speed of light in a vacuum to the speed of light in the medium. When light enters a material with a different density, its speed changes, which causes the light to bend or refract. This bending can be described by Snell's Law, which relates the angle of incidence to the angle of refraction based on the refractive indices of the two media involved.

Understanding the refractive index is crucial in fields such as optics, where it helps explain phenomena like the bending of light through lenses and the altering of appearance in submerged objects. It essentially quantifies how much light is affected by the medium it travels through, making it a fundamental concept in physics and engineering.