Editing Refraction (section)

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

For light, refraction follows [[Snell's law]], which states that, for a given pair of media, the ratio of the sines of the [[angle of incidence (optics)|angle of incidence]] <math>{\theta_1} </math> and [[angle of refraction]] <math>{\theta_2} </math> is equal to the ratio of [[phase velocities]] <math display="inline">\frac{v_1}{v_2}</math> in the two media, or equivalently, to the [[refractive index|refractive indices]] <math display="inline">\frac{n_2}{n_1}</math> of the two media:<ref>{{Cite book|title=[[Principles of Optics]]|last=Born and Wolf|publisher=Pergamon Press INC.|year=1959|location=New York, NY|pages=37}}</ref>

<math display="block">\frac{\sin\theta_1}{\sin\theta_2} =\frac{v_1}{v_2}=\frac{n_2}{n_1}</math>


[[File:Pen in water.jpg|thumb|A pen partially submerged in a bowl of water appears bent due to refraction at the water surface.]]