Electric force (${\mathbf{F}}_E=q\mathbf{E}$)

The electric force on an electric charge $q$ is ${\mathbf{F}}_E=q\mathbf{E}$, using the electric field of the other sources and excluding the charge's own self-field. Positive electric charge gives force along the electric field; negative electric charge reverses it. A field $\mathbf{E}=400N/C\hat{\mathbf{x}}$ therefore gives ${\mathbf{F}}_E=-8\times 10^{-7}\mathrm{N}\hat{\mathbf{x}}$ on $q=-2\mathrm{nC}$. This is the electric part of the Lorentz force; the magnetic contribution is $q\mathbf{v}\times \mathbf{B}$. ^[ref].

The electric force exerted by a time-independent electric field. For a point charge, the external field excludes its own singular self-field. The method of images evaluates conductor-induced forces by the image field at the physical charge's position; the fictitious images need not be physical charges in the conductor interior.