Optics/Refraction

thumb|right|When light travels from one medium to another, it bends. Refraction is the change in direction and phase velocity of a wave due to a change in the medium in which the wave is traveling. A wave which undergoes this phenomenon is said to have been refracted. This phenomenon is most commonly observed when a wave passes from one medium to another at any angle other than 90° or 0°. Refraction is described by Snell's law (also known as the Snell–Descartes law and the law of refraction), which states that for a given pair of media and a wave with a single frequency, the ratio of the sines of the angle of incidence and angle of refraction is equivalent to the ratio of phase velocities in the two media, or equivalently, to the opposite ratio of the indices of refraction : When a wave travels across an interface and into a medium with a higher index of refraction, the wave bends towards the normal. If a wave travels across an interface and into a lower index of refraction, the wave bends away from the normal. If a wave travels across an interface and into a medium with the same index of refraction, the direction of the wave's propagation does not change. The two most common indices of refraction used when first exploring the topic of refraction are air () and water (). To simplify calculations, the index of refraction of air is typically approximated to be (which is actually the index of refraction of a vacuum). thumbnail|right|Demonstration of no refraction at angles greater than the critical angle. As the angle of incidence increases, the angle of refraction also increases. There comes a point in which the angle of refraction is 90° and means that the wave refracts parallel to the interface. This angle is called the critical angle and for angles greater than or equal to the critical angle, refraction does not take place and all of the light is reflected; this phenomenon is called total internal reflection and will be covered in the next section. + Some representative refractive indicesMaterialλ (nm)nRef.Vacuum 1 (per definition) Air at STP 1.000277 Gases at 0 °C and 1 atmAir589.291.000293 Alfred Zajac Hecht, Eugene; Cummings, Eugene Optics, Fourth Edition Pearson Higher Education 18 March 2003 978-0-321-18878-6Carbon dioxide589.291.00045 Morgan Introduction to Geometrical and Physical Optics McGraw-Hill Book Company, INC. 1953 Hodgman Selby, Weast Handbook of Chemistry and Physics Chemical Rubber Publishing Co. 1957 Pedrotti Pedrotti, Pedrotti Introduction to Optics, Third Edition Pearson Prentice Hall 221 2007 0-13-149933-5 Helium589.291.000036Hydrogen589.291.000132Liquids at 20 °C Arsenic trisulfide and sulfur in methylene iodide 1.9Meyrowitz, R, A compilation and classification of immersion media of high index of refraction, American Mineralogist 40: 398 (1955)Benzene589.291.501Carbon disulfide589.291.628Carbon tetrachloride589.291.461Ethyl alcohol (ethanol)589.291.361Silicone oil 1.52045Silicon and Oil Refractive Index StandardsWater589.291.3330 Solids at room temperatureTitanium dioxide (Rutile phase )589.292.496RefractiveIndex.INFO - Refractive index and related constantsDiamond589.292.419Strontium titanate589.292.41Amber589.291.55Fused silica (also called Fused Quartz)589.291.458Sodium chloride589.291.544 Raymond A. Serway Faughn, Jerry S. College Physics, 6th Edition Brooks/Cole 692 2003 978-0-03-035114-3 Other materialsLiquid helium 1.025Water ice 1.31Cornea (human) 1.373/1.380/1.401 Patel S Marshall J, Fitzke FW 3rd. Refractive index of the human corneal epithelium and stroma J Refract Surg. 11 2 100–105 1995 Mar-Apr 7634138 Lens (human) 1.386 - 1.406Acetone 1.36Ethanol 1.36Glycerol 1.4729Bromine 1.661Teflon AF 1.315 http://www2.dupont.com/Teflon_Industrial/en_US/products/product_by_name/teflon_af/properties.html Teflon AF 2010-10-14Teflon 1.35 - 1.38Cytop 1.34 http://www.agcce.eu.com/CYTOP/TechInfo.asp Cytop 2010-10-14Sylgard 184 1.4118 http://www1.dowcorning.com/DataFiles/090007c8802d7bc4.pdf 184 Silicone Elastomer Dow Corning Product Information PDF 2012-12-11 http://web.archive.org/web/20130314075539/http://www1.dowcorning.com/DataFiles/090007c8802d7bc4.pdf 2013-03-14PLA 1.46http://onlinelibrary.wiley.com/doi/10.1002/9780470649848.ch8 Poly(Lactic Acid): Synthesis, Structures, Properties, Processing, and Applications; Chapter 8: Optical Properties 2012-10-25Acrylic glass 1.490 - 1.492Polycarbonate 1.584 - 1.586PMMA 1.4893 - 1.4899PETg 1.57PET 1.5750Crown glass (pure) 1.50 - 1.54Flint glass (pure) 1.60 - 1.62Crown glass (impure) 1.485 - 1.755Flint glass (impure) 1.523 - 1.925Pyrex (a borosilicate glass) 1.470http://www.matter.org.uk/schools/Content/Refraction/absolute.html Absolute Refractive Index 2007-10-18 University of LiverpoolCryolite 1.338Rock salt 1.516Sapphire 1.762–1.778Sugar Solution, 25% 1.3723http://www.frederiksen.eu/fileadmin/user_upload/PDF/Export_Manuals/545920_AE_sugarsolution.pdf Manual for Sugar solution Prism 2012-3-21Sugar Solution, 50% 1.4200Sugar Solution, 75% 1.4774Cubic zirconia 2.15 - 2.18Potassium Niobate (KNbO3) 2.28Moissanite 2.65 - 2.69Cinnabar (Mercury sulfide) 3.02Gallium(III) phosphide 3.5Gallium(III) arsenide 3.927 Zinc Oxide3902.4Germanium 4.01Silicon 590 3.96http://pvcdrom.pveducation.org/APPEND/OPTICAL.HTM Optical Properties of Silicon 2009-05-31 See also A-level Physics (Advancing Physics)/Refraction