Functions to get electrostatic fields from known solutions (infinite charged wires, infinite charge sheet)

[qudsiramiz]

In addition to the Biot-Savart law solver proposed in #99 and other one in #100, we should have a way of calculating the electric fields resulting from simple charge distributions using Coulomb's Law. This would include the electric field from an finite/infinite linear charge (which has a simple exact solution) and the electric field resulting from an infinite sheet or dipole (which has a complicated exact solution) for boundary conditions at infinity. There might be other analytical solutions worth including, but these two are probably the most important ones.

This can get added to plasmapy.formulary.electrostatistics

PS: Was suggested by Daniel Prater