Refractive index: Difference between revisions

Revision as of 23:49, 22 July 2025

Revision as of 09:45, 5 August 2025

Line 7:

The refractive index, <math>n</math>, can be seen as the factor by which the speed and the [[wavelength]] of the radiation are reduced with respect to their vacuum values: the speed of light in a medium is {{math|1=''v'' = c/''n''}}, and similarly the wavelength in that medium is {{math|1=''λ'' = ''λ''₀/''n''}}, where {{math|''λ''₀}} is the wavelength of that light in vacuum. This implies that vacuum has a refractive index of 1, and assumes that the [[frequency]] ({{math|1=''f'' = ''v''/''λ''}}) of the wave is not affected by the refractive index.

The refractive index may vary with wavelengthwavelenth. This causes white light to split into constituent colors when refracted. This is called [[dispersion (optics)|dispersion]]. This effect can be observed in [[Prism (optics)|prisms]] and [[rainbow]]s, and as [[chromatic aberration]] in lenses. Light propagation in [[Absorption (electromagnetic radiation)|absorbing]] materials can be described using a [[complex number|complex]]-valued refractive index.<ref name="Attwood">{{cite book|title=Soft X-rays and extreme ultraviolet radiation: principles and applications|author=Attwood, David |page=60|isbn=978-0-521-02997-1|year=1999|publisher=Cambridge University Press }}</ref> The [[Imaginary number|imaginary]] part then handles the [[attenuation]], while the [[Real number|real]] part accounts for refraction. For most materials the refractive index changes with wavelength by several percent across the visible spectrum. Consequently, refractive indices for materials reported using a single value for {{mvar|n}} must specify the wavelength used in the measurement.

The concept of refractive index applies across the full [[electromagnetic spectrum]], from [[X-ray]]s to [[radio wave]]s. It can also be applied to [[wave]] phenomena such as [[sound]]. In this case, the [[speed of sound]] is used instead of that of light, and a reference medium other than vacuum must be chosen.<ref name=Kinsler>{{cite book | last = Kinsler | first = Lawrence E. | title = Fundamentals of Acoustics | url = https://archive.org/details/fundamentalsacou00kins_265 | url-access = limited | publisher = John Wiley | year = 2000 | isbn = 978-0-471-84789-2 | page = [https://archive.org/details/fundamentalsacou00kins_265/page/n151 136]}}</ref> Refraction also occurs in oceans when light passes into the [[halocline]] where salinity has impacted the density of the water column.