The drift velocity equals the product of this quantity and mobility, and the Poisson equation is derived by eliminating this quantity by substitution. The displacement field equals the polarization density plus the product of this quantity and the permittivity. This quantity falls off with the cube of distance for dipole configurations. The path integral of it is equal to the time derivative of the magnetic flux, and its divergence is proportional to the charge density. For 10 points, name this 
The drift velocity equals the product of this quantity and mobility, and the Poisson equation is derived by eliminating this quantity by substitution. The displacement field equals the polarization density plus the product of this quantity and the permittivity. This quantity falls off with the cube of distance for dipole configurations. The path integral of it is equal to the time derivative of the magnetic flux, and its divergence is proportional to the charge density. For 10 points, name this physical quantity which when multiplied by a test charge gives an inverse-square force, a result of Coulomb's Law.
The drift velocity equals the product of this quantity and mobility, and the Poisson equation is derived by eliminating this quantity by substitution.
electric field [prompt on E-field]