Editing Refractive index (section)

===Reflectivity===
Apart from the transmitted light there is also a [[reflection (physics)|reflected]] part. The reflection angle is equal to the incidence angle, and the amount of light that is reflected is determined by the [[reflectivity]] of the surface. The reflectivity can be calculated from the refractive index and the incidence angle with the [[Fresnel equations]], which for [[normal incidence]] reduces to<ref name = bornwolf />{{rp|44}}

<math display="block">R_0 = \left|\frac{n_1 - n_2}{n_1 + n_2}\right|^2\!.</math>

For common glass in air, {{math|''n''{{sub|1}} {{=}} 1}} and {{math|''n''{{sub|2}} {{=}} 1.5}}, and thus about 4% of the incident power is reflected.<ref name=ri-min>{{cite web |last=Swenson |first=Jim |quote=Incorporates Public Domain material from the [[U.S. Department of Energy]] |title=Refractive Index of Minerals |series=Newton BBS / Argonne National Laboratory |publisher=US DOE |date=November 10, 2009 <!--[http://www.newton.dep.anl.gov/]--> |url=http://www.newton.dep.anl.gov/askasci/env99/env234.htm|access-date=2010-07-28 |url-status=live |archive-url=https://web.archive.org/web/20100528092315/http://www.newton.dep.anl.gov/askasci/env99/env234.htm |archive-date=May 28, 2010}}</ref> At other incidence angles the reflectivity will also depend on the [[polarization (waves)|polarization]] of the incoming light. At a certain angle called [[Brewster's angle]], ''p''-polarized light (light with the electric field in the [[plane of incidence]]) will be totally transmitted. Brewster's angle can be calculated from the two refractive indices of the interface as <ref name=Hecht/>{{rp|245}}
<math display="block"> \theta_\mathsf{B} = \arctan \left( \frac{n_2}{n_1} \right) ~.</math>