In an experiment to determine e/m using Thomson's method, electrons from the cathode accelerate through a potential difference of 1.5 kV. The collimated beam of electrons is made to enter a region of crossed electric and magnetic fields, both perpendicular to beam direction. Two parallel plates 2.0 cm apart held at a potential difference of 400 V provide the electric field. while a magnetic field of `8.6 xx 10^(-4)T` is produced by Helmholtz coils arrangement. The beam hits the fluorescent screen at the end of the tube undeflected. Determine the charge to mass ratio of electron.