Definition:CGS Unrationalised Electromagnetic System

Definition
The CGS unrationalised electromagnetic system of units is a system of measurement in the field of electromagnetism.

This is obtained by taking as the basis the equation for the Force between Infinite Parallel Straight Conductors carrying Steady Current:


 * $\mathbf F \propto \dfrac {2 I_1 I_2} r$

where:
 * $\mathbf F$ denotes the force between two parallel infinitely long conductors in a vacuum carrying steady currents $I_1$ and $I_2$
 * $r$ denotes the distance between $s_1$ and $s_2$.

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 current is the same in both conductors: $I_1 = I_2 = I$

The base unit of electric current is defined to be the electromagnetic unit:


 * the electric current $I$ such as to produce a force of $1$ dyne between the two conductors when positioned $1$ centimetre apart.

The constant of proportion plays the same role in this equation as the vacuum permeability of the SI system.

As a consequence of this, the vacuum permittivity works out as being $\dfrac 1 {c^2}$.