Vacuum permittivity

Vacuum permittivity, denoted ε₀, is the physical constant that sets the strength of electric interactions in vacuum and relates electric fields to charge in Maxwell’s equations.

Coulomb's law: The law giving the electrostatic force between two point charges in terms of their charges and separation. In SI units, ε₀ sets the proportionality between charge and electrostatic force.
International System of Units: The internationally agreed system of measurement units, abbreviated SI. The SI system specifies how ε₀ is expressed and measured.
Electric charge: A property of matter that produces and responds to electromagnetic forces. Charge is the source quantity linked to electric fields through ε₀.
Relative permittivity: The dimensionless ratio of a material’s permittivity to vacuum permittivity. It describes a material relative to ε₀ rather than the vacuum constant itself.
Gauss's law: A relation stating that electric flux through a closed surface is proportional to the enclosed charge. Its vacuum form connects electric flux to charge through ε₀.
2019 redefinition of the SI base units: A revision that fixed values of seven defining constants to establish the SI units. It ended ε₀’s exact-value status by fixing the elementary charge instead.
Electric field: A vector field representing the force per unit positive test charge at each point. ε₀ connects electric field strength to charge in vacuum.
Permittivity of free space: A traditional name for vacuum permittivity, ε₀. This commonly used phrase names the same constant, not a separate quantity.
Maxwell's equations: Four equations describing how electric and magnetic fields are produced and how they change. ε₀ appears in the equations governing electric fields and electromagnetic waves.
Elementary charge: The magnitude of the electric charge carried by a proton, exactly fixed in the SI system. Fixing this charge made ε₀ experimentally determined rather than exact by definition.

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