Why does a prism separate light into a spectrum of colors?

If all wavelengths of light were refracted by the same amount when entering and leaving a prism then there would be no separation of colors. The refractive index of all materials depends on the wavelength of light. In diamond the refractive index for blue is 1.594, for red 1.571. In flint glass the index varies from 1.528 to 1.514. In crown glass the variation is from 1.528 to 1.514, while in water it is only 1.340 to 1.331. In all cases the refractive index of blue is larger than that of red, so the blue light is refracted through a larger angle than the red. The large difference in diamonds accounts for their “flash.”


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