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: vphase = c/(sqrt(εr*μr)) where vphase is the phase velocity. c is the speed of light in a vacuum. εr is the relative permittivity. μr is the relative permability. Then to get the wavelength we do like this: λ = vphase/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??