An electron is projected with an initial speed  $u=4\times {10}^{6}m{s}^{-1}$  into the uniform field between the parallel plates in figure. The direction of the field in vertically downward, and the field is zero except in the space between the plates. The electron enters the filed, at a point midway between the plates. If the electron just misses the upper plate as it emerges from the field, find the magnitude of the electric field in  $N{C}^{-1}$ (charge of electron $e=1.6\times {10}^{-19}$ and mass of electron $=9.1\times {10}^{-31}$  )