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`epsilon_0 = 8.854187817" x "10^-12 "C"^2 /( J*m )`

8.85418782E-12

The physical constant, `epsilon_0`, is commonly called the **vacuum permittivity**, **permittivity of free space**, or **electric constant**. The permittivity of free space is the value of the absolute (not relative) dielectric permittivity of the classical vacuum. This constant relates the units for electric charge to mechanical quantities such as length and force.

This constant is usually represented in farads per meter `"F"/m`, and sometimes in units of `C^2 /( J*m )`.

This is an exactly known value, as it is derived from two exactly known constants:

`epsilon_0 = 1/(mu_0 *c^2)`