In Fig. 28-58, an electron of mass m, charge e, and low (negligible) speed enters the region

Question:

In Fig. 28-58, an electron of mass m, charge e, and low (negligible) speed enters the region between two plates of potential difference V and plate separation d, initially headed directly toward the top plate. A uniform magnetic field of magnitude B is normal to the plane of the figure. Find the minimum value of B such that the electron will not strike the top plate.