Refractive index
Ratio of light speed in vacuum to that in a medium.
The refractive index (also called refraction index or index of refraction), often denoted n, is the ratio of the speed of light in vacuum (c) to the speed of light in a given optical medium (v), n=c/v. It determines how much the path of light is bent when entering a material, as described by Snell's law, and also influences reflection, total internal reflection, and Brewster's angle. The concept applies across the full electromagnetic spectrum and to wave phenomena such as sound.
- field
- Optics
- known_for
- Ratio of speed of light in vacuum to speed in a medium; determines refraction and dispersion
- symbol
- n (gradually prevailed over m and µ)
- typical_range_visible
- Between 1 and 2 for most transparent media
Lore & Background
At the same time he changed this value of refractive power into a single number, instead of the traditional ratio of two numbers.
Reader's Guide
The refractive index is a fundamental optical property that quantifies how much light slows down when passing through a material, relative to its speed in vacuum. It is central to Snell's law of refraction, which describes how light bends at interfaces, and also governs reflection intensity, total internal reflection, and Brewster's angle. The refractive index varies with wavelength, causing dispersion—the splitting of white light into colors—observable in prisms, rainbows, and chromatic aberration in lenses. For absorbing materials, a complex-valued refractive index is used, with the imaginary part handling attenuation. The concept extends beyond visible light to the entire electromagnetic spectrum and even to sound waves. In practical applications, high refractive index materials allow for thinner, lighter lenses, while plastics offer lower density alternatives. The refractive index can be less than 1 for phase velocities exceeding the speed of light in vacuum, as occurs near resonance frequencies, in plasmas, and for X-rays.
Did You Know?
- Gases at atmospheric pressure have refractive indices close to 1 due to their low density.
- For visible light, most transparent media have refractive indices between 1 and 2.
More in Electromagnetism And Waves 1-23
Spotted an error? Know more?
This is a living reference — every entry is fact-audited, and reader corrections feed straight into our audit queue. Suggest an edit · See this site's audit record