ON APPROXIMATE FORMULAS FOR THE ELECTROSTATIC FORCE BETWEEN 2 CONDUCTING SPHERES

A series expression for the electrostatic force between two charged co nducting spheres having equal radii and charges is derived using the m ethod of electrical images. This expression is a special case of that for two spheres with arbitrary charges and radii, found by Maxwell usi ng zonal harmonics, Keeping in mind the use of approximate formulas fo r the interpretation of classroom measurements of the electrostatic fo rce between spheres, we comment on two incorrect approximate formulas and examine the contribution of the first few non-Coulomb terms of the comet formula by comparing with values obtained using a computational approach. (C) 1998 American Association of Physics Teachers.