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**Calculating wavelength in a media**

Hi

Trying to get how to calculate the wavelength of an electromagnetic wave in a media and I am getting confused about the permittivity.

I know the formula:

v

_{phase}= c/(sqrt(ε

_{r}*μ

_{r}))

where v

_{phase}is the phase velocity.

c is the speed of light in a vacuum.

ε

_{r}is the relative permittivity.

μ

_{r}is the relative permability.

Then to get the wavelength we do like this:

λ = v

_{phase}/f

where λ is the wavelength and f the frequency.

This is all well and good, but isn't there a real and imaginary part to the permittivity? Is only the real part used or is the entire complex number used in which case you end up with a complex distance??

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