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
Famous quotes containing the word definition:
“I’m beginning to think that the proper definition of “Man” is “an animal that writes letters.””
—Lewis Carroll [Charles Lutwidge Dodgson] (1832–1898)
“It’s a rare parent who can see his or her child clearly and objectively. At a school board meeting I attended . . . the only definition of a gifted child on which everyone in the audience could agree was “mine.””
—Jane Adams (20th century)
“... we all know the wag’s definition of a philanthropist: a man whose charity increases directly as the square of the distance.”
—George Eliot [Mary Ann (or Marian)