An electrostatic CRT has parallel deflection plates 1.5 cm long and 6mm apart. The screen is 55cm from the centre of the deflecting plates. The deflecting and accelerating potentials are 150 V and 2.5 kilovolts respectively. Determine the:

 Ld = length of deflecting plates, m

 d = distance between deflecting plates,m

m = mass of the electron ,kg

L = distance between screen and the centre of the deflecting plates, m

Ea = accelerating voltage to the plates, volts

Ed = deflecting potential of the plates

(I) Velocity of the electron

Soln

Velocity of electron,  Vox = √{(2eEa)/(m)}

Ea = 2500 v

Ed = 150v

Ld = 1.5cm

L = 55cm

d = 6 mm

m = 9.1094 x 10^-31 kg

e = 1.6022 x 10^ -19 Coulombs

= {√ (2 x 1.6022 x 10^-19 x 2500)/(9.1094x 10^-31)}

= √ 8.794x 10^ 14

= 29655037.64 m/s

(II) Amount of deflection

D = {((L x Ld x Ed)/(2 x d x Ea)) x (m)}

    = {((0.55 x 0.015 x 150)/(2 x 6 x 10^-3 x 2500))}

    = 0.04125 m

(III) Deflection sensitivity

  

          = { ( Ld x L )/(2 x d x Ea)}

          = { ( 1.5 x 10^ -2 x 0.55)/(2 x 6 x 10^ -3 x 2500)}

          = 2.75 x 10^ -4 m/ volt

(IV) Deflection factor

           = 1/deflection sensitivity

            = 1/ ( 2.75 x 10^ -4)

            = 3636.3636 volt/meter