  A new operator for pion photo- and electroproduction has been developed for
nuclear applications at photon equivalent energies up to 1 GeV. The model
contains Born terms, vector mesons and nucleon resonances ($P_{33}(1232)$,
$P_{11}(1440)$, $D_{13}(1520)$, $S_{11}(1535)$, $F_{15}(1680)$, and
$D_{33}(1700)$). The resonance contributions are included taking into account
unitarity to provide the correct phases of the pion photoproduction multipoles.
The $Q^2$ dependence of electromagnetic resonance vertices is described with
appropriate form factors in the electromagnetic helicity amplitudes. Within
this model we have obtained good agreement with the experimental data for pion
photo- and electroproduction on the nucleon for both differential cross
sections and polarization observables. The model can be used as a starting
point to predict and analyze forthcoming data.
