in ac fields permittivity becomes complex quantity and has real and imaginary parts. in metals (may be few exceptions but i dont know) imaginary part is always positive and represents loss factor or energy absorbed. why the plot of imaginary part of dielectric constant as function of energy is exponentially decaying curve (it decreases with the increase in energy)?secondly img. part of dielectric constant is also related to conductivity so can we infer that energy lost to the metals appears as conductivity? but then it is directly proportional to conductivity but conductivity plots (as function of energy again) show structures. finally permittivity becomes complex because ac fields are complex or their is any other reason? i am studying electrodynamics of continuous media of landau and lifgarbagez.