Definition
Three equivalent definitions of α in terms of other fundamental physical constants are:
where:
- e is the elementary charge;
- ħ = h/2π is the reduced Planck constant;
- c is the speed of light in vacuum;
- ε0 is the electric constant or permittivity of free space;
- or µ0 is the magnetic constant or permeability of free space;
- or ke is the Coulomb constant.
In electrostatic cgs units, the unit of electric charge, the statcoulomb, is defined so that the Coulomb constant, ke, or the permittivity factor, 4πε0, is 1 and dimensionless. Then the expression of the fine-structure constant becomes the abbreviated
an expression commonly appearing in physics literature.
Read more about this topic: Fine-structure Constant
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