The Zeeman effect, which is a phenomenon
that describes the splitting of a single
in a magnetic field
into several closely spaced spectral lines. There are two different types of Zeeman effect, Normal
physicist Pieter Zeeman
won a share
of the Nobel Prize
in 1902 for discovering the former.
According to classical physics, a spectral line is formed when an electron moves from one discrete energy level to another inside the atom. Thus when the line is placed in an external magnetic field, the electron is given extra energy so that the original line splits into three – one at the original frequency of the line, one higher and one lower.
However, this did not explain the splitting of a single line into more than three sub-lines. It was not until the advent of quantum physics that the Zeeman effect was truly explained.
Two Dutch physicists, Samuel Goudsmit and George Uhlenbeck, in 1925 postulated the existence of spin angular momentum. An electron has an intrinsic magnetic moment due to its orbital angular momentum, L, associated with it; these can only be in certain alignments. They postulated that an electron also has spin angular momentum, S, associated it, where spin is either 0 or 1. The orbital angular momentum and spin angular momentum combine to make total angular momentum, J.
Therefore, the external magnetic field together with the intrinsic angular momentum of the electron combine to give extra energy thus the electron is able to move into a different energy level. Thus the classical effect is explained by the electrons have spin = 0 and the anomalous effect is explained by spin = 1.