Is permittivity/permeability ratio constant or not in media?

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SUMMARY

The ratio of permittivity to permeability is constant in a vacuum but varies in different media. In materials, the relative permittivity (ε_r) and relative permeability (μ_r) are independent and depend on the atomic, molecular, and bulk properties of the substance. For instance, water exhibits a relative permittivity of approximately 80 at low frequencies and about 1.8 at optical frequencies due to the polarization of water molecules. In contrast, relative permeability remains close to 1 across various frequencies, except in ferromagnetic materials.

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We have a constant ratio of them in vacuum. Is it same in a medium also? Or not? And in any case, what is the reason?
 
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In a medium, ##\epsilon## and ##\mu## are independent of each other, as far as I know. They depend on the atomic/molecular/bulk properties of the material.
 
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\epsilon_r (relative permittivity) is usually frequency-dependent, to a greater or lesser degree. A favourite example is water, whose \epsilon_r at very low frequencies is about 80, but at optical frequencies (around 5 \times 10^{14} Hz, is about 1.8. This is because water molecules are strongly polarised, and at low frequencies can align themselves strongly with the electric field. At high frequencies they can't flail about (librate?) fast enough to keep pace with the changing field. Except for ferromagnetic materials, \mu_r (relative permeability) is pretty much 1 at all frequencies.
 
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