Two plane metal plates 4 cm long are held horizontal 3 cm apart in a vacuum one being vertically one above other. The upper plate is at a p. d 300 volt and the lowered is earthed. Electrons having velocity of 10^7 m/s are injected horizontally midway between the plate and in a direction parallel to the 4cm edge. Calculate the vertical deflection of the electron beam as it emerges from the plates. (e/m=1.8 x 10^11Ckg^- 1).​