spin angular momentum. The spin -factor is approximately two: . The magnetic moment of an electron is approximately twice what it should be in classical mechanics. The factor of two implies that the electron appears to be twice as effective in producing a magnetic moment as the corresponding classical charged body. The spin magnetic dipole moment is approximately one B because and the electron is a spin- particle (): The component of the electron magnetic moment is where s is the spin quantum number. Note that is a negative constant multiplied by the spin, so the magnetic moment is antiparallel to the spin angular momentum. The spin g-factor comes from the Dirac equation, a fundamental equation connecting the electron's spin with its electromagnetic properties. Reduction of the Dirac equation for an electron in a magnetic field to its non-relativistic limit yields the Schrödinger equation with a correction term, which takes account of the interaction of the electron's intrinsic magnetic moment with the magnetic field giving the correct energy. For the electron spin, the most accurate value for the spin -factor has been experimentally determined to have the value Note that this differs only marginally from the value from the Dirac equation. The small correction is known as the anomalous magnetic dipole moment of the electron; it arises from the electron's interaction with virtual photons in quantum electrodynamics. A triumph of the quantum electrodynamics theory is the accurate prediction of the electron g-factor. The CODATA value for the electron magnetic moment is Orbital magnetic dipole moment The revolution of an electron around an axis through another object, such as the nucleus, gives rise to the orbital magnetic dipole moment. Suppose that the angular momentum for the orbital motion is . Then the orbital magnetic dipole moment is Here L is the electron orbital -factor and B is the Bohr magneton. The value of L is exactly equal to one, by a quantum-mechanical argument analogous to the derivation of the classical gyromagnetic ratio. Total magnetic dipole moment The total magnetic dipole moment resulting from both spin and orbital angular momenta of an electron is related to the total angular momentum by a similar equation: The -factor J is known as the Landé g-factor, which can be related to L and S by quantum mechanics. See Landé g-factor for details. Example: hydrogen atom For a hydrogen atom, an electron occupying the atomic orbital