Hi everyone, My very first post after simply using physicsforums as a (very) handy FAQ resource. Okay, so my question is probably pretty simple, but I've been unable to find anything on here already. How does a complex dielectric constant imply the absorption of EM radiation? I understand that the frequency dependence of the dielectric constant can be expressed as a complex function, but can't seem to understand mathematically how the imaginary part of the function corresponds to a loss of energy (wave) to the medium (dielectric)... implying absorption. Three resources I've used seem to make the mathematical and physical arguments pertaining to my question too quickly for me to understand, so any help is greatly appreciated! Cheers, Adam.