Spin and Addition of Angular Momenta

In this section, we discover that elementary particles, such as electrons or quarks, possess internal degrees of freedom. In other words, a wavefunction alone is no longer sufficient to describe them. Let us consider again the hydrogen atom ( \(Z=1\) ) from the previous chapter and immerse it in a spatially uniform magnetic field \(\textbf{B}\) . As we know, due to the presence of the magnetic field, the Hamiltonian changes. In Eq. ( 4.60 ), we precisely derived the form of the Hamiltonian that suits our case, i.e., that of a particle exposed to a uniform magnetic field.