[UPSC CSE 2008] Nuclear Physics (Q153, 20M)

In the Lorentz model for dispersion, the uniform dielectric medium is assumed to be a collection of oscillators with number density N, natural frequency $ \omega_0 $ and decay constant $ \gamma $. Find the complex susceptibility $ \chi $ of such a medium. In the frequency dependence of the real part of $ \chi $ identify the regions of normal and anomalous dispersion.