Refractive index: Difference between revisions

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The refractive index may vary with wavelength. 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 | author = Kinsler, 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>
 
For [[lens]]es (such as [[eye glasses]]), a lens made from a high refractive index material will be thinner, and hence lighter, than a conventional lens with a lower refractive index. Such lenses are generally more expensive to manufacture than conventional ones.