  By using the Debye screened potential a generalized version of Newton's Shell
Theorem is developed and analytical equations are derived to calculate i) the
potential of a charged sphere surrounded by electrolyte, ii) the potential of
two concentric charged spheres surrounded by electrolyte, and iii) the membrane
potential of a charged lipid vesicle surrounded by electrolyte with high ion
concentration. By numerical integration the potential of a lipid vesicle is
calculated at any electrolyte concentration.
