Plasma is a mixture of charged particles and neutral particles. The mixture is quasineutral. Plasma is characterized by two independent parameters for each of the particle species. These are particle density and temperature. There are some applications where the thermal effects are unimportant. Such a plasma is called a cold plasma. A Lorentz plasma is a further simplification of the medium. In this model, it is assumed that electrons interact with each other only through collective space charge forces and that heavy positive ions and neutral particles are at rest. Plasma can be modeled as a dielectric. However, its dielectric constant depends on the frequency of the signal. This dependence makes it highly dispersive and leads to a qualitative difference in the properties of waves scattered by a temporal change in the electron density of the plasma medium as compared with such scattering by a pure dielectric.