Consider the refractive index of free electrons in copper, at frequencies around the plasma frequency, ωp in the Drude model. Write expressions for the reflectivity R at normal incidence as a function of frequency  in the vicinity of ωp. For copper the free electron relaxation time is 1.9 x10-14 s and the plasma energy is 7.8 eV.

Anonzero net force acts on a particle and does work. which one of the following statements is true? the kinetic energy of the particle changes, but the speed of the particle does not change. the kinetic energy of the particle does not change, but the speed of the particle does change. the kinetic energy of the particle changes, but the velocity of the particle does not change. the kinetic energy and the speed of the particle change, but the velocity of the particle does not change. the kinetic energy, speed, and velocity of the particle change.