This course is a continuation of Physics 420. Topics include: angular momentum, basic properties and eigenvalues of angular momentum operator, addition of angular momentum, the two-particle problem and the hydrogen atom, hydrogenci wave functions, elements of matrix mechanics, spin wave functions, basis and representations, energy representations, angular momentum matrices, Pauli spin matrices, magnetic moment of an electron, addition of spins, time-independent perturbations theory, fine structure of hydrogen atom, Aeeman effect, time dependent perturbation theory, two-level system, emission and absorption of radiation, spontaneous emission, the variational principle and scattering theory.