Editing Refractive index (section)

===Refraction===
{{Main|Refraction}}

[[File:Snells law.svg|thumb|alt=refer to caption|[[Refraction]] of light at the interface between two media of different refractive indices, with ''n''<sub>2</sub> > ''n''<sub>1</sub>. Since the [[phase velocity]] is lower in the second medium (''v''<sub>2</sub> < ''v''<sub>1</sub>), the angle of refraction ''θ''<sub>2</sub> is less than the angle of incidence ''θ''<sub>1</sub>; that is, the ray in the higher-index medium is closer to the normal.]]

When light moves from one medium to another, it changes direction, i.e. it is [[Refraction|refracted]]. If it moves from a medium with refractive index {{math|''n''{{sub|1}}}} to one with refractive index {{math|''n''{{sub|2}}}}, with an [[angle of incidence (optics)|incidence angle]] to the [[surface normal]] of {{math|''θ''{{sub|1}}}}, the refraction angle {{math|''θ''{{sub|2}}}} can be calculated from [[Snell's law]]:<ref>R. Paschotta, article on [https://www.rp-photonics.com/refraction.html refraction] {{webarchive|url=https://web.archive.org/web/20150628174941/https://www.rp-photonics.com/refraction.html |date=2015-06-28 }} in the [https://www.rp-photonics.com/encyclopedia.html Encyclopedia of Laser Physics and Technology] {{webarchive|url=https://web.archive.org/web/20150813044135/http://www.rp-photonics.com/encyclopedia.html |date=2015-08-13 }}, accessed on 2014-09-08</ref>
<math display="block">n_1 \sin \theta_1 = n_2 \sin \theta_2.</math>

When light enters a material with higher refractive index, the angle of refraction will be smaller than the angle of incidence and the light will be refracted towards the normal of the surface. The higher the refractive index, the closer to the normal direction the light will travel. When passing into a medium with lower refractive index, the light will instead be refracted away from the normal, towards the surface.