Where r is radii (m), q₁ and q₂ are charge (coulombs), is the permittivity (J^-1 C² m^-1), is the vacuum permittivity (J^-1 C² m^-1), and is the relative permittivity.

To graph the potential energy (J) enter the parameters (i.e., q₁, q₂, relative permittivity) and hit New Plot. 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 on/off 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 and hold.