In a perpendicular electric field, the force acts on the electron in the opposite direction of electric field. Hence the deflection is in the plane of electric field. In this case, the speed of the electron changes and hence kinetic energy of the moving electron changes in the electric field. In a perpendicular to the plane of its direction of motion as well as of magnetic field. Hence the deflection of the electron beam is perpendicular to the plane of the magnetic field. In this case, the work done by the force due to magnetic field acting on the moving electron is zero. Therefore, the kinetic energy of the moving electron does not change in the magnetic field.
