Consider two charged parallel plates with infinite dimensions that are separated by a distance of .5m. Take one section of each of the plates such that the section is square with side 1m. The plates have charge densities of +s and-s. (A charge density describes the amount of charge per unit area. Visually, every part of the plate is charged, so field lines emanate from every part of the plate. In diagrams, drawing more or fewer field lines per unit area shows the relative strength of the field.) Since the sections under consideration are sections of infinite plates, fringing effects may be ignored (the field generated by the edges of the square sections).
