Editing Magnetic quantum number (section)

== Effect in magnetic fields ==
The quantum number <math>m_l</math> refers, loosely, to the direction of the  [[angular momentum]] [[Vector (geometric)|vector]].  The magnetic quantum number <math>m_l</math> only affects the electron's energy if it is in a magnetic field because in the absence of one, all spherical harmonics corresponding to the different arbitrary values of <math>m_l</math> are equivalent.  The magnetic quantum number determines the energy shift of an [[atomic orbital]] due to an external magnetic field (the [[Zeeman effect]]) &mdash; hence the name ''magnetic'' quantum number.  However, the actual [[magnetic dipole moment]] of an electron in an atomic orbital arises not only from the electron angular momentum but also from the electron spin, expressed in the spin quantum number.

Since each electron has a magnetic moment in a magnetic field, it will be subject to a torque which tends to make the vector <math>\mathbf{L}</math> parallel to the field, a phenomenon known as [[Larmor precession]].