Electron scattering and charged pion photoproduction at 200MeV on 12C and I3C have been studied by the nuclear shell model to investigate M1 and E2 nuclear form factors of the isovector type. Starting with the Op-shell model of Hauge-Maripuu, the effects of core polarization by the M3 Y force and the one-pion-exchange current are taken into account. The effect of core polarization is found to be essential in both electron scattering and pion photoproduction, while the meson-exchange current, which also improves the calculated results, gives contributions of about 10 ~-15 ~.