What is the definition of refractive index?

The definition of refractive index is the speed of light in a given material divided by the speed of light in a vacuum. This concept is fundamental in optics and describes how much the path of light is bent, or refracted, when it enters a material from air or another medium.

The refractive index is a dimensionless number that indicates how much slower light travels in a medium compared to its speed in a vacuum. If the refractive index is greater than 1, which it usually is for most materials, it signifies that light travels slower in that material. For example, water has a refractive index of around 1.33, indicating that light travels 1.33 times slower in water than in a vacuum.

This definition is crucial for understanding various optical phenomena, such as the bending of light, which is related to the principles of lenses, prisms, and other optical devices. The relationship defined by the refractive index is pivotal in fields ranging from physics and engineering to medical technology, where precise optical measurements can impact diagnostics and treatment methods.