{"id":476,"date":"2026-07-13T21:08:10","date_gmt":"2026-07-13T21:08:10","guid":{"rendered":"https:\/\/physicsfundamentalsinfo.com\/blog\/?p=476"},"modified":"2026-07-13T23:30:12","modified_gmt":"2026-07-13T23:30:12","slug":"dispersion-of-light","status":"publish","type":"post","link":"https:\/\/physicsfundamentalsinfo.com\/blog\/waves\/dispersion-of-light\/","title":{"rendered":"Dispersion of Light and Prisms"},"content":{"rendered":"\n
Definition<\/div>

\n\nDispersion of light is the splitting of white light into its constituent colours when it passes through a transparent medium such as a glass prism, because the refractive index \u2014 and therefore the speed and bending of light \u2014 depends on its wavelength. Shorter wavelengths (violet) slow and bend the most; longer wavelengths (red) bend the least.\n\n<\/p><\/div>\n\n

Look at a rainbow arcing over wet fields, or the buried flash of colour deep inside a cut diamond, and you are watching one quiet rule of physics at work. White light is not a single thing \u2014 it is a bundle of colours travelling together, and the right piece of glass or water can pull them apart.<\/p>\n\n

That unbundling is dispersion. It is why a cheap glass prism throws a spectrum across your wall, why the sky answers a rainstorm with colour, and why the lens in a phone camera has to fight faint coloured fringes. Once you understand the mechanism, you start to see it everywhere.<\/p>\n\n

What Is Dispersion of Light?<\/h2>\n\n

Dispersion of light is the separation of white light into its component colours as it passes through a medium, caused by the refractive index of that medium changing with wavelength. Because each colour bends by a slightly different amount, they emerge fanned out into a spectrum instead of staying blended.<\/p>\n\n

Isaac Newton settled the question in the 1660s. Passing sunlight through a prism, he saw the familiar band of red, orange, yellow, green, blue and violet. The clever part came next: a second prism recombined the colours back into white light. That proved the prism was not adding<\/em> anything \u2014 the colours were inside the white light all along, waiting to be spread out.<\/p>\n\n

The visible spectrum runs from roughly 400 nm (violet) to 700 nm (red). Each of those wavelengths corresponds to a colour your eye reads, and \u2014 crucially \u2014 to a slightly different refractive index inside glass. Hold that one idea and the rest of dispersion follows.<\/p>\n\n<\/rect><\/polygon>Glass prism<\/text>A<\/text><\/line><\/line>White light<\/text><\/line><\/line><\/line><\/line><\/line><\/line><\/line>Red<\/text>Yellow<\/text>Blue<\/text>Violet<\/text><\/svg>\n\n

White light entering a prism is bent twice. Violet is deviated most and red least, so the beam leaves fanned into a spectrum.<\/p>\n\n

The Formulas Behind Dispersion of Light<\/h2>\n\n

Dispersion has no single master equation \u2014 it emerges from the law of refraction fed by one fact: the refractive index n<\/strong> is a function of wavelength. Start with Snell’s law, which governs how any ray bends at a boundary.<\/p>\n\n

n1<\/sub> sin \u03b81<\/sub> = n2<\/sub> sin \u03b82<\/sub><\/div>\n\n