Addition of angular momenta Lec-2 part 3

The addition of angular momenta is encountered in all areas of modern physics. Mastering its techniques is essential for an understanding of the various subatomic phenomena. For instance, the total angular momentum of the electron in a hydrogen atom consists of two parts, an orbital part L, which is due to the orbiting motion of the electron around the proton, and a spin part S which is due to the spinning motion of the electron about itself. The properties of the hydrogen atom cannot be properly discussed without knowing how to add the orbital and spin parts of the electron’s total angular momentum. In what follows we are going to present the formalism of angular momentum addition and then consider some of its most essential applications.