The reason the speed of light is different for different colors and different in a refractive medium, such as glass, is because the speed of propagation of light depends on the electromagnetic properties of the medium, which, in turn, sometimes depend on the frequency of the propagating wave. This phenomenon is called dispersion.
Recall that light is an electromagnetic wave which propagates in vacuum with the speed `c=3*10^8 m/s` . When the light enters...
The reason the speed of light is different for different colors and different in a refractive medium, such as glass, is because the speed of propagation of light depends on the electromagnetic properties of the medium, which, in turn, sometimes depend on the frequency of the propagating wave. This phenomenon is called dispersion.
Recall that light is an electromagnetic wave which propagates in vacuum with the speed `c=3*10^8 m/s` . When the light enters different medium, its speed reduces by the factor of
`n=1/sqrt(epsilon*mu)` , where `epsilon` is the dielectric constant and `mu` is relative magnetic permeability of the medium. These quantities indicate how the medium responds to the external electromagnetic field.
The factor n is called the index of refraction of the medium. The index of refraction of the air (which is where we usually see visible light), it is very close to 1. In the common refractive media, such as glass or water, the index of refraction changes with the frequency of the incident visible light, because the electromagnetic properties of these media, measured by `epsilon` and `mu` , are affected differently by the electromagnetic waves with different frequencies. So, the speed of each color in the refractive medium will be
`v=c/(n(f))` , where n(f) is the index of refraction different for each color, or frequency, of light.
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