Why does light refract?


Quick Answer

Light refracts because of the differential slowing of light of different wavelengths as it passes through a medium. This means that light, which is normally made up of various wavelengths of electromagnetic radiation, reacts to a medium such as liquid or glass by slowing down. This slowing is uneven, and the rate depends on the exact wavelength of light.

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Why does light refract?
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Full Answer

The theory of relativity imposes a maximum speed on light, but there is no restriction on how much it can be slowed as it passes through a medium. As light of diverse wavelengths enters a slow medium, the different wavelengths of light react to the change in medium by slowing at different rates. This bends the light, sometimes dramatically.

When refraction is done in a prism, whether natural or artificial, the result of this differential bending is that white sunlight gets spread out into its constituent colors. Each color is just a wavelength of light, and each can be isolated from the others by passing the light through a medium with a sufficiently high refractive index. When the refraction is done in a laboratory, the result is a spectrum that is useful to study. When the refraction is done by raindrops in the air, the result is a rainbow.

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