Snell's Law | Definition, Formula, & Facts - Britannica

Ask the Chatbot Games & Quizzes History & Society Science & Tech Biographies Animals & Nature Geography & Travel Arts & Culture ProCon Money Videos Snell’s law Introduction References & Edit History Related Topics Images & Videos Contents Science Physics Matter & Energy CITE verifiedCite While every effort has been made to follow citation style rules, there may be some discrepancies. Please refer to the appropriate style manual or other sources if you have any questions. Select Citation Style MLA APA Chicago Manual of Style Copy Citation Share Share Share to social media Facebook X URL https://www.britannica.com/science/Snells-law Feedback External Websites Feedback Corrections? Updates? Omissions? Let us know if you have suggestions to improve this article (requires login). Feedback Type Select a type (Required) Factual Correction Spelling/Grammar Correction Link Correction Additional Information Other Your Feedback Submit Feedback Thank you for your feedback

Our editors will review what you’ve submitted and determine whether to revise the article.

External Websites

• LSU Scholarly Repository - Snell's law of refraction observed in thermal frontal polymerization (PDF)
• Nature - Scientific Reports - The role of Snell�s law for a magnonic majority gate
• Hamilton College - Snell�s Law
• The Physics Classroom - Snell's Law
• The University of Southern Mississippi - The Aquila - Snell's Law of Refraction Observed in Thermal Frontal Polymerization (PDF)
• BCCampus Publishing - The Law of Refraction � Snell�s Law
• New York University - Department of Physics - Snell�s law
• MIT OpenCourseWare - 2D and 3D Waves, Snell's Law
• Engineering LibreTexts - Snell's Law

Snell’s law physics Ask Anything Homework Help Written and fact-checked by Britannica Editors Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree.... Britannica Editors History Britannica AI Ask Anything Table of Contents Table of Contents Ask Anything

Snell’s law, in optics, a relationship between the path taken by a ray of light in crossing the boundary or surface of separation between two contacting substances and the refractive index of each. This law was discovered in 1621 by the Dutch astronomer and mathematician Willebrord Snell (also called Snellius). The account of Snell’s law went unpublished until its mention by Christiaan Huygens in his treatise on light. In the Figure, n1 and n2 represent the indices of refraction for the two media, and α1 and α2 are the angles of incidence and refraction that the ray R makes with the normal (perpendicular) line NN at the boundary. Snell’s law asserts that n1/n2 = sin α2/sin α1.

Because the ratio n1/n2 is a constant for any given wavelength of light, the ratio of the two sines is also a constant for any angle. Thus, the path of a light ray is bent toward the normal when the ray enters a substance with an index of refraction higher than the one from which it emerges; and because the path of a ray of light is reversible, the ray is bent away from the normal when entering a substance of lower refractive index.

Key People: Willebrord Snell (Show more) Related Topics: refraction (Show more) See all related content

The reason light is refracted in going from one medium to another is shown in the Figure. According to Huygens’s principle, each point on a wave front of light is a source of new wavelets. A parallel beam, consisting of the three rays R1, R2, and R3, is incident on a boundary plane AF separating two media of indices n1 and n2, and it has a plane wave front ABC. In this example, the speed of light is greater in the first medium than in the second (n1 is less than n2). Consequently, according to Huygens’s principle, the radius of the wavelets in the first medium is greater than the radius in the second. By the time a point C on the wave front ABC has moved from C to F on the plane, the point A of the wave front has moved a distance of only AD in the second medium. A plane DEF tangent to the new wavelets represents the new wave front, and lines perpendicular to it represent the paths taken by the rays in the second medium.

More From Britannica optics: Graphical ray tracing The Editors of Encyclopaedia Britannica This article was most recently revised and updated by Erik Gregersen.