Which statement about dispersion is true?

Which statement about dispersion is true?

• A. Dispersion is an optical property that varies by material.
• B. Dispersion is measured by the RI difference between the violet and red light rays in a material.
• C. Dispersion is not related to the refractive index.
• D. Dispersion is identical for all materials.

Answer: (B)

Dispersion is about how much a material bends different colors of light by different amounts when light passes through it. The key is that the refractive index changes with wavelength, so blue and violet light bend more than red light. To quantify this effect, we look at how much the refractive index differs between violet light and red light. This difference, n(violet) minus n(red), is a direct measure of a material’s dispersive power. The larger that Δn is, the more the colors spread apart and the more pronounced the fire or spectral separation you’ll see in a gemstone. Since dispersion hinges on how refractive index changes with wavelength, this measure is the most precise way to describe dispersion across materials. The other statements either misstate the relationship to refractive index or claim dispersion is the same for all materials, which isn’t the case.

Dispersion is about how much a material bends different colors of light by different amounts when light passes through it. The key is that the refractive index changes with wavelength, so blue and violet light bend more than red light. To quantify this effect, we look at how much the refractive index differs between violet light and red light. This difference, n(violet) minus n(red), is a direct measure of a material’s dispersive power. The larger that Δn is, the more the colors spread apart and the more pronounced the fire or spectral separation you’ll see in a gemstone. Since dispersion hinges on how refractive index changes with wavelength, this measure is the most precise way to describe dispersion across materials. The other statements either misstate the relationship to refractive index or claim dispersion is the same for all materials, which isn’t the case.