Editing Light (section)

===Refraction===
{{Main|Refraction}}
[[File:Optical refraction at water surface.jpg|thumb|Due to refraction, the straw dipped in water appears bent and the ruler scale compressed when viewed from a shallow angle.]]

Refraction is the bending of light rays when passing through a surface between one transparent material and another. It is described by [[Snell's Law]]:

:<math>n_1\sin\theta_1 = n_2\sin\theta_2\ .</math>

where θ<sub>1</sub> is the angle between the ray and the surface [[Normal (geometry)|normal]] in the first medium, θ<sub>2</sub> is the angle between the ray and the surface normal in the second medium and n<sub>1</sub> and n<sub>2</sub> are the [[Index of refraction|indices of refraction]], ''n'' = 1 in a [[vacuum]] and ''n'' > 1 in a [[Transparency and translucency|transparent]] [[Chemical substance|substance]].

When a beam of light crosses the boundary between a vacuum and another medium, or between two different media, the wavelength of the light changes, but the frequency remains constant. If the beam of light is not [[orthogonality|orthogonal]] (or rather normal) to the boundary, the change in wavelength results in a change in the direction of the beam. This change of direction is known as [[refraction]].

The refractive quality of [[lens (optics)|lenses]] is frequently used to manipulate light in order to change the apparent size of images. [[Magnifying glass]]es, [[Glasses|spectacles]], [[contact lens]]es, [[microscope]]s and [[refracting telescope]]s are all examples of this manipulation.