Refractive Index | Definition & Equation - Britannica

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External Websites

• University of Toronto Scarborough - Chemistry Online - Refractive Index Theory
• Al-Mustaqbal University - Refractive index (PDF)
• Introduction to Petrology - Light and Optics Part 2: Refractive Index, Polarized Light, Birefringence
• National Center for Biotechnology Information - Refractive Index
• California Institute of Technology - The Feynman Lectures on Physics - The Origin of the Refractive Index
• CORE - Two-dimensional refractive index profiling of optical fibers by modified refractive near-field technique (PDF)
• Weber State University - Refractive Index (PDF)
• University of Arizona - Wyant College of Optical Sciences - Refractive Index and Dispersion (PDF)
• IOPscience - Journal of Physics: Conference Series - Determination of refractive index on three mediums based on the principle of refraction of light (PDF)

refractive index physics Ask Anything Also known as: index of refraction, mutual refractive index, refractive constant(Show More) 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 Last updated Nov. 21, 2025 •History Britannica AI Ask Anything Table of Contents Table of Contents Ask Anything

refractive index, measure of the bending of a ray of light when passing from one medium into another. If i is the angle of incidence of a ray in vacuum (angle between the incoming ray and the perpendicular to the surface of a medium, called the normal) and r is the angle of refraction (angle between the ray in the medium and the normal), the refractive index n is defined as the ratio of the sine of the angle of incidence to the sine of the angle of refraction; i.e., n = sin i / sin r. Refractive index is also equal to the velocity of light c of a given wavelength in empty space divided by its velocity v in a substance, or n = c/v.

Also called: index of refraction (Show more) Related Topics: light refraction (Show more) On the Web: National Center for Biotechnology Information - Refractive Index (Nov. 21, 2025) (Show more) See all related content

Some typical refractive indices for yellow light (wavelength equal to 589 nanometres [10−9 metre]) are the following: air, 1.0003; water, 1.333; crown glass, 1.517; dense flint glass, 1.655; and diamond, 2.417. The variation of refractive index with wavelength is the source of chromatic aberration in lenses. The refractive index of X-rays is slightly less than 1.0, which means that an X-ray entering a piece of glass from air will be bent away from the normal, unlike a ray of light, which will be bent toward the normal. The equation n = c/v in this case indicates, correctly, that the velocity of X-rays in glass and in other materials is greater than its velocity in empty space.

This article was most recently revised and updated by Adam Augustyn.