Electromagnetism Units
In SI units, electric charge is expressed in coulombs, a separate unit which is additional to the "mechanical" units (mass, length, time), even though the traditional definition of the ampere refers to some of these other units. In natural unit systems, however, electric charge has units of 1/2 3/2 −1.
There are two main natural unit systems for electromagnetism:
- Lorentz–Heaviside units (classified as a rationalized system of electromagnetism units).
- Gaussian units (classified as a non-rationalized system of electromagnetism units).
Of these, Heaviside-Lorentz is somewhat more common, mainly because Maxwell's equations are simpler in Lorentz-Heaviside units than they are in Gaussian units.
In the two unit systems, the elementary charge e satisfies:
- (Lorentz–Heaviside),
- (Gaussian)
where ħ is the reduced Planck constant, c is the speed of light, and α≈1/137 is the fine-structure constant.
In a natural unit system where c=1, Lorentz-Heaviside units can be derived from SI units by setting ε0 = μ0 = 1. Gaussian units can be derived from SI units by a more complicated set of transformations, such as dividing all electric fields by, multiplying all magnetic susceptibilities by 4π, and so on.
Read more about this topic: Natural Units
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