We consider a transmission through the potential relief created by a split gate constriction (quantum point contact). Simultaneously, dc and ac voltages Vup (t) = V0 + V1 cos ?t and Vdw (t) = V0 + V1 cos (?t+?) are applied to the gates. We show numerically that the in-phase ac voltages (?=0) smear the conductance steps of the stationary conductance, while the antiphase ac voltages (?=p) only shift the conductance steps. Moreover, computation of currents in probing wires connected cross to the time-periodic quantum point contact reveals a net current for ? 0,p. This implies that the Schrödinger equation described by the electron transport under the effect of the time-periodic long electrodes is equivalent to the transmission in the crossed effective magnetic and electric fields, where the in-plane magnetic field b~? is directed along the transport axis and the electric field e~? is directed perpendicular to the plane of electron transport. Then the vector e×b gives rise to the galvanomagnetic current directed cross to the electron transport. © 2007 The American Physical Society.