What effect earned Pieter Zeeman the 1902 Nobel Prize in Physics?

The Zeeman effect earned Pieter Zeeman the 1902 Nobel Prize in Physics.

Zeeman discovered that spectral lines split into multiple components when the light source is placed in a magnetic field. This observation showed that magnetic fields affect the motion and energy of charged particles inside atoms.

Hendrik Lorentz provided the theoretical explanation, and the two Dutch physicists shared the 1902 Nobel Prize. Their work helped establish the relationship between electromagnetism and atomic structure before quantum mechanics was fully developed.

The Zeeman effect is not the same as the Stark effect. The Zeeman effect involves an external magnetic field, whereas the Stark effect involves an external electric field. The splitting can be simple or more complicated depending on the atom’s angular momentum and the strength of the field, making the effect useful in spectroscopy and astrophysics.