Physics/Essays/Fedosin/Fine structure constant
< Physics < Essays < FedosinIn physics, the fine structure constant (usually denoted α, the Greek letter alpha) is a fundamental physical constant, namely the coupling constant characterizing the strength of the electromagnetic interaction. Being a dimensionless quantity, it has constant numerical value in all systems of units. Arnold Sommerfeld introduced the fine-structure constant in 1916.
The current recommended value of α is 7.29735257×10−3. [1]
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 vacuum permittivity;
- or µ0 is the vacuum permeability;
- 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.
Additional notes
Main source of the article is Wikipedia article fine-structure constant.
Many of articles in Wikiversity make reference to the fine structure constant, or discuss its relationship to other physical quantities. Examples are:
- Planck scale
- Stoney scale
- Strong gravitational constant
- Selfconsistent gravitational constants
- Selfconsistent electromagnetic constants
- Gravitational characteristic impedance of free space
- Magnetic coupling constant
References
- ↑ "CODATA Value: fine-structure constant". The NIST Reference on Constants, Units, and Uncertainty. US National Institute of Standards and Technology. June 2011. Retrieved 2011-06-23.