Fig. 2 and Fig. 3 show the effect of applied field on droplet diameter and formation frequency. The application of the electric potential to the nozzle leads to the reduction of the drop diameter and an increase of the dripping frequency. The droplet diameter is not significantly affected by the flow rate [13]. However, the flow rate does affect the dripping frequency. This implies that drop formation in this mode is governed essentially by a quasi-static force balance, i.e. the liquid inertia has negligible effect on droplet formation. Therefore increasing the flow rate merely increases the droplet frequency as clearly observed in Fig. 3. This features forms the basis of modelling described below.