Suppose that instead of a harmonic oscillator, we have a metal in which the electrons move directly in response to the electric field, that is, there is a damping constant but no spring constant, so that ω₀ = 0. What is the susceptibility χ(ω) in the limit ω→ 0? Using the formula (3.8.7) for the reflectivity, what does this imply about the infrared reflectance of a metal? 

Show that if  Γ ≡ 1/τ , the solution is consistent with the formula J = σE, where σ is given by (5.8.6).

r] =r|| = t = t|| = zu - lu Tu + Tu 2n1 n + n (3.8.7)