# Why 3 lines in Zeeman effect?

by Ruptor
Tags: effect, lines, zeeman
 P: 886 In the case of the normal Zeeman effect, we don't need to consider electron spin. Then you only need to care about the z component of angular momentum quantum number m. The allowable transitions in LS coupling have delta m = {-1, 0, or 1}. This gives you three lines.The presence of the magnetic field causes the energy of an "m" state to be shifted by $\mu_B B m$. This energy shift happens to both the upper levels and lower levels of the transition, so only the change in m matters.