Refractive index & dielectric constant

[Kolahal Bhattacharya]

We know,n=(rel.permittivityxrel.permeability)^(1/2)
For natural transperant mediums (to visible light of EM spectrum)are non-magnetic.So, rel.permeability=1
hence n=(dielectric constant)^(1/2)
Book says this is not valid for all materials,as dielectric constant is frequency dependent.Why yhis is not the case with vacuum?
As far as I know, we are familiar to r.i. s which are measured at the frequency of visible light.Book says dielectric constant are measured at much lower frequency.Why?why not we measure it at optical frequency?Wikipedia says static dielectric constant is a good approx.for altering field of low frequency--why?

 

[Andrew Mason]

We know,n=(rel.permittivityxrel.permeability)^(1/2)
For natural transperant mediums (to visible light of EM spectrum)are non-magnetic.So, rel.permeability=1
hence n=(dielectric constant)^(1/2)
Book says this is not valid for all materials,as dielectric constant is frequency dependent.Why yhis is not the case with vacuum?
As far as I know, we are familiar to r.i. s which are measured at the frequency of visible light.Book says dielectric constant are measured at much lower frequency.Why?why not we measure it at optical frequency?Wikipedia says static dielectric constant is a good approx.for altering field of low frequency--why?

There are no electric dipoles in empty space.

It is the electric dipoles (polar molecules) in the dielectric which reduce the applied field, but these do not respond quickly enough at light frequencies (the polar molecules can't turn quickly enough). So the dielectric strength has to be measured at lower frequencies.

AM

 

[kyle8921]

I can provide some information regarding the refractive index and dielectric constant. The refractive index (n) is a measure of how much light is refracted when passing through a material, and it is related to the dielectric constant (ε) by the equation n=(εμ)^1/2, where μ is the permeability of the material.

It is true that for natural transparent materials, the permeability is typically equal to 1, as they are non-magnetic. However, this does not necessarily mean that the dielectric constant is solely dependent on the frequency of light. While it is true that the dielectric constant can vary with frequency, this is not always the case. In vacuum, the dielectric constant is equal to 1, regardless of the frequency of light. This is because vacuum is considered an ideal insulator, with no free charges to respond to the electric field of light.

The reason why dielectric constants are often measured at lower frequencies, rather than optical frequencies, is due to practical reasons. It is easier and more accurate to measure dielectric constants at lower frequencies, as the effects of imperfections and impurities in the material are minimized. Additionally, some materials have a high dielectric constant at optical frequencies, making it difficult to accurately measure.

Lastly, while the static dielectric constant may be a good approximation for low frequency fields, it may not accurately represent the behavior of the material at higher frequencies. This is because at higher frequencies, the material may exhibit different properties and responses to the electric field. Therefore, it is important to consider the frequency dependence of the dielectric constant when studying the properties of a material.