Page "Electronvolt" Paragraph 21

The dimensions of momentum units are M < sup > 1 </ sup > L < sup > 1 </ sup > T < sup >-1 </ sup >.

The dimensions of energy units are M < sup > 1 </ sup > L < sup > 2 </ sup > T < sup >-2 </ sup >.

Then, dividing the units of energy ( such as eV ) by a fundamental constant that has units of velocity ( M < sup > 0 </ sup > L < sup > 1 </ sup > T < sup >-1 </ sup >), facilitates the required conversion of using energy units to describe momentum.

In the field of high-energy particle physics, the fundamental velocity unit is the speed of light c. Thus, dividing energy in eV by the speed of light in vacuum, one can describe the momentum of an electron in units of eV / c.