A charged particle of m and charge Q has acquired a certain velocity by passing through a potential di Iierence `U_o`. With this velocity it flies into the field of a parallel-plate capacitor, with the distance between the plates being L, the potential di fference bei ng U. The velocity of the particle is directed parallel to the plates. Where should the magnetic field that makes the particle move along a straight line in the capacitor be directed and what should its value be (the induction B) ?