Exchange currents for systems of extended nucleons

A prescription for calculating the electromagnetic-exchange currents by requiring gauge invariance of the equations of motion is given within the framework of a nonrelativistic potential model. The obtained formula is applied to the one-meson exchange potential with spatially extended meson-nucleon vertices. It is shown that the minimal substitution in meson-nucleon vertices with hadronic form factors induces the additional exchange current. It is found that the current is identical with that derived by Gross and Riska from the continuity-equation constraint imposed on the dressed photon-meson vertex. (orig.)