2 plane parallel conducting plates are held horizontal,one above the other in a vacuum.Electrons having a speed of 6×10^6 m/s and moves normally to the plates enter the region between them through a hole in the lower plate which is earthed.What potential must be applied to the other plate so that the electrons just fails to reach it?What is the subsequent motion of these electrons? (ratio of charge to mass of electron= 1.8×10^(11) Ckg^(−1) )