It has recently been suggested that the plasmasphere of the Earth is peeled off near midnight (at L= 4.5 for Kp = 1-2) by 'Plasma Elements Interchange Motion' driven by centrifugal or inertial forces. McIlwain's(1974) convection electric field model E3H with a variable scale factor f has been used to calculate different plasmapause positions and shapes. The new theoretical models obtained with f∼-1.2 are in agreement with observations of whistlers and of the PROGNOZ satellites, for periods of very low geomagnetic activity (i.e. Kp < 1). Furthermore the numerical models corresponding to f∼-0.7 fit qualitatively the observations of the plasmasphere and plasmapause when the geomagnetic activity has a higher constant level (i.e. 2 <Kp< 4). A tentative relation between f and Kp is deduced.