Fig 3F.3 - Variation of the Coulomb Interaction Energy with Distance Between Two Point Charges

The potential energy for two charges and its dependence on their separation is given by

Where r is the separation (nm), Q₁and Q₂ are charge (coulombs), ε is the permittivity (J^-1·C²·m^-1), ε₀ is the vacuum permittivity (J^-1·C²·m^-1), and ε_r is the relative permittivity.

To graph the potential energy (zJ) enter Q₁ and Q₂, relative permittivity and click New Plot. Note Q₁ and Q₂ are entered as integer multiples of the charge of an electron. Up to 5 plots can be displayed at one time. The Clear button will remove all plots. To see the parameters for each plot hit the Legend button. The Redraw button will refresh the graph. This is useful when the function domain (i.e., r ) has been changed. To see the value of each plot at a given point, move your cursor to the desired location then click.