$($c$)$ An electrostatically deflected cathode ray tube has plane parallel deflecting plates which are $4$ cm long $2$ cm apart and the distance from their center to screen is $30$ cm $.$The final anode voltage is $3000$ V $.$Calculate the deflecting voltage required to cause the beam to strike the deflection plates and the corresponding deflection on the screen deflection on the screen. Evaluate the bandwidth of CRT$.$