The refractive index of material of prism is different for different colours of light because the speed of different colours is different inside the prism. Thus, the light of different colours is deviated through different angles, by a prism. What happens when a ray of ordinary light passes through the prism?
Why do red and blue light travel differently?
Why does blue light scatter more than red light?
What is Rayleigh scattering?
What would happen if a material lacked dispersion?
Why does light travel slower in a medium?
What is the difference between blue and red light?
How does velocity relate to wavelength?
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Why do red and blue light travel differently?
So the answer to your question is that red and blue are refracted differently because ultima tely they are made up of different wavelength photons, and though the individual photons all travel at speed c in vacuum inbetween the atoms of the medium (when measured locally), the interaction (scattering) between the photons and the atoms is wavelength dependent, and this causes the wavefront to slow down differently for different wavelength light.
Why does blue light scatter more than red light?
Since different wavelength photons scatter differently (because scattering is wavelength dependent) on the atoms of the medium, the wavefront will slow down differently in the case of different wavelength light. Blue wavelength photons have a shorter wavelength (relative to red wavelength) and so blue wavelength is a little bit closer to the size of the atoms in the medium, so blue will scatter more then red. The visible wavelength you are asking about is still much larger then the atoms' size in the medium, thus Rayleigh (elastic) scattering is the correspondent way, by the way this is the same reason the sky is blue.
What is Rayleigh scattering?
Rayleigh scattering (/ˈreɪli/ RAY-lee), named after the nineteenth-century British physicist Lord Rayleigh (John William Strutt), [1] is the predominantly elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the radiation. For light frequencies well below the resonance frequency of the scattering particle (normal dispersion regime), the amount of scattering is inversely proportional to the fourth power of the wavelength.
What would happen if a material lacked dispersion?
If a material lacked dispersion (had constant index of refraction across wavelength) then red and blue light would have the same velocity and refract with the same angle. Most materials, however, do exhibit dispersion. For example glass does which is why a prism can be used to decompose white light into it's various wavelength components.
Why does light travel slower in a medium?
But because there is interaction between the photons and the atoms in the medium, the wavefront slows down, this is what we mean when we say that light travels slower (relatively then in vacuum) in a medium.
What is the difference between blue and red light?
blue light meaning that red and blue light 1) have different velocities in the material and 2) refract at different angles at interfaces with the material.
How does velocity relate to wavelength?
Velocity is equal to the product of a wave's frequency times its wavelength and, as the frequency of light remains the same as it changes media, the only thing that does differ is the velocity and the wavelength. Snell's law states that v 2 v 1 gives us the refractive index of light. As the wavelength of different colors of light varies, so do their speeds (in a non-vacuum medium). The greater the wavelength, the greater the speed, causing a difference in the refractive index. As there is a difference in the wavelength of red (about 700 nm) and blue (about 500 nm), they have different speeds in the same medium (other than vacuum/air) leading to different refractive indexes.