Definition:CGS Unrationalised Electrostatic System
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Definition
The CGS unrationalised electrostatic system of units is a system of measurement in the field of electromagnetism.
From Coulomb's Law of Electrostatics, the force between two stationary charged particles $a$ and $b$ is given by:
- $\mathbf F_{a b} \propto \dfrac {q_a q_b {\mathbf r_{a b} } } {r^3}$
where:
- $\mathbf F_{a b}$ is the force exerted on $b$ by the electric charge on $a$
- $\mathbf r_{a b}$ is the displacement vector from $a$ to $b$
- $r$ is the distance between $a$ and $b$.
- the constant of proportion is defined as being positive.
Let us arrange it such that:
- $\mathbf F$ is expressed in dynes
- $r$ is expressed in centimetres
- the constant of proportion is taken to be $1$
- the charge is the same on both charged particles: $q_1 = q_2 = Q$
The base unit of electric charge is defined to be the electrostatic unit:
- the electric charge $Q$ such as to produce a force of $1$ dyne between the $a$ and $b$ when positioned $1$ centimetre apart.
The constant of proportion plays the same role in this equation as the vacuum permittivity of the SI system.
As a consequence of this, the vacuum permeability works out as being $\dfrac 1 {c^2}$.
Sources
- 1964: Milton Abramowitz and Irene A. Stegun: Handbook of Mathematical Functions ... (previous) ... (next): $2$. Physical Constants and Conversion Factors