1. The problem statement, all variables and given/known data The index of refraction is given by n^2 = (N q / ε m) (1 / (ω0^2 - ω^2 + iγω)) Where N is the electron density, q is the charge of an electron, ε is the permittivity of free space, m is the mass of an electron, ω0 is the resonant frequency, ω is the incident frequency, and γ is the friction coefficient. Consider the case of a free electron with a friction coefficient given by interactions with positive ions. What is n^2 for this case? 2. The attempt at a solution I'm not super sure how to approach this problem. I figure that ω0 has to be 0 for free electrons, but I'm not sure what to do with the friction term. A gentle nudge in the right direction would be greatly appreciated.