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electric constant[i¦lek·trik ′kän·stənt]
(or permittivity of free, or empty, space), the constant of proportionality ∊0 in Coulomb’s law, which gives the force of interaction between two point charges at rest.
In the International System of Units (SI), ∊0 = 10 7/4πC 2 farads per meter (F/m) = 8.85418782 ± 0.00000007 F/m, where c is the speed of light in m/sec. In the centimeter-gram-second (cgs) electrostatic system and in the Gaussian system, ∊0 is taken to be a dimensionless factor equal to unity.
In contrast to the dielectric constant ∊, which depends on the type of substance, temperature, pressure, and other parameters, the electric constant ∊0 depends only on the choice of a system of units.