∇ · E = ρ / ε0
∇ x E = 0
where ρ is the volume charge density (C/m3), and ε0
is the permittivity of free space, which is 10-9/(36∏) (F/m).
These two postulates state that a static electric field is irrotational and its divergence is ρ / ε0.
ρ / ε0 can be used to determine whether a field is electrostatic field or not.
