## 12. Angular momentum

The quantum mechanics of angular momentum is fascinating. It is also very basic to much of quantum mechanics. It is a model for dealing with other systems of particles

In chapter 5.4, it was already mentioned that angular momentum of particles comes in two basic kinds. Orbital angular momentum is a result of the angular motion of particles, while spin is built-in angular momentum of the particles.

Orbital angular momentum is usually indicated by and spin angular momentum by . A system of particles will normally involve both orbital and spin angular momentum. The combined angular momentum is typically indicated by

However, this chapter will use as a generic name for any angular momentum. So in this chapter can indicate orbital angular momentum, spin angular momentum, or any combination of the two.

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