< Optics
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 θ1 and angle of refraction θ2 is equivalent to the ratio of phase velocities (v1 / v2) in the two media, or equivalently, to the opposite ratio of the indices of refraction (n2 / n1):

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 (n=1.00029) and water (n=1.33). To simplify calculations, the index of refraction of air is typically approximated to be n=1.00 (which is actually the index of refraction of a vacuum).

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 indices
Materialλ (nm)nRef.
Vacuum1 (per definition)
Air at STP1.000277
Gases at 0 °C and 1 atm
Air589.291.000293[1]
Carbon dioxide589.291.00045[2]

[3] [4]

Helium589.291.000036[1]
Hydrogen589.291.000132[1]
Liquids at 20 °C
Arsenic trisulfide and sulfur in methylene iodide1.9[5]
Benzene589.291.501[1]
Carbon disulfide589.291.628[1]
Carbon tetrachloride589.291.461[1]
Ethyl alcohol (ethanol)589.291.361[1]
Silicone oil1.52045[6]
Water589.291.3330[1]
Solids at room temperature
Titanium dioxide (Rutile phase )589.292.496[7]
Diamond589.292.419[1]
Strontium titanate589.292.41
Amber589.291.55[1]
Fused silica (also called Fused Quartz)589.291.458[1]
Sodium chloride589.291.544[8]
Other materials
Liquid helium1.025
Water ice1.31
Cornea (human)1.373/1.380/1.401[9]
Lens (human)1.386 - 1.406
Acetone1.36
Ethanol1.36
Glycerol1.4729
Bromine1.661
Teflon AF1.315[10]
Teflon1.35 - 1.38
Cytop1.34[11]
Sylgard 1841.4118[12]
PLA1.46[13]
Acrylic glass1.490 - 1.492
Polycarbonate1.584 - 1.586
PMMA1.4893 - 1.4899
PETg1.57
PET1.5750
Crown glass (pure)1.50 - 1.54
Flint glass (pure)1.60 - 1.62
Crown glass (impure)1.485 - 1.755
Flint glass (impure)1.523 - 1.925
Pyrex (a borosilicate glass)1.470[14]
Cryolite1.338
Rock salt1.516
Sapphire1.762–1.778
Sugar Solution, 25%1.3723[15]
Sugar Solution, 50%1.4200[15]
Sugar Solution, 75%1.4774[15]
Cubic zirconia2.15 - 2.18
Potassium Niobate (KNbO3)2.28
Moissanite2.65 - 2.69
Cinnabar (Mercury sulfide)3.02
Gallium(III) phosphide3.5
Gallium(III) arsenide3.927
Zinc Oxide3902.4
Germanium4.01
Silicon5903.96[16]

See also

  1. 1 2 3 4 5 6 7 8 9 10 11 Optics, Fourth Edition. Pearson Higher Education. 18 March 2003. ISBN 978-0-321-18878-6.
  2. ↑ Introduction to Geometrical and Physical Optics. McGraw-Hill Book Company, INC.. 1953.
  3. ↑ Handbook of Chemistry and Physics. Chemical Rubber Publishing Co.. 1957.
  4. ↑ Introduction to Optics, Third Edition. Pearson Prentice Hall. 2007. p. 221. ISBN 0-13-149933-5.
  5. ↑ Meyrowitz, R, A compilation and classification of immersion media of high index of refraction, American Mineralogist 40: 398 (1955)
  6. ↑ Silicon and Oil Refractive Index Standards
  7. ↑ RefractiveIndex.INFO - Refractive index and related constants
  8. ↑ College Physics, 6th Edition. Brooks/Cole. 2003. p. 692. ISBN 978-0-03-035114-3.
  9. ↑ "Refractive index of the human corneal epithelium and stroma". J Refract Surg. 11 (2): 100–105. 1995 Mar-Apr. PMID 7634138.
  10. ↑ "Teflon AF". http://www2.dupont.com/Teflon_Industrial/en_US/products/product_by_name/teflon_af/properties.html. Retrieved 2010-10-14.
  11. ↑ "Cytop". http://www.agcce.eu.com/CYTOP/TechInfo.asp. Retrieved 2010-10-14.
  12. ↑ "184 Silicone Elastomer" (PDF). Dow Corning. Archived from the original on 2013-03-14. http://web.archive.org/web/20130314075539/http://www1.dowcorning.com/DataFiles/090007c8802d7bc4.pdf. Retrieved 2012-12-11.
  13. ↑ "Poly(Lactic Acid): Synthesis, Structures, Properties, Processing, and Applications; Chapter 8: Optical Properties". http://onlinelibrary.wiley.com/doi/10.1002/9780470649848.ch8. Retrieved 2012-10-25.
  14. ↑ University of Liverpool. "Absolute Refractive Index". http://www.matter.org.uk/schools/Content/Refraction/absolute.html. Retrieved 2007-10-18.
  15. 1 2 3 "Manual for Sugar solution Prism". http://www.frederiksen.eu/fileadmin/user_upload/PDF/Export_Manuals/545920_AE_sugarsolution.pdf. Retrieved 2012-3-21.
  16. ↑ "Optical Properties of Silicon". http://pvcdrom.pveducation.org/APPEND/OPTICAL.HTM. Retrieved 2009-05-31.
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