Step-by-step explanation:
It is given that,
Distance between two conducting plates, d = 21 cm = 0.21 m
Electrostatic force acting on the electron placed anywhere between the two plates,

(a) Let E is the electric field at the position of the electron. The electric force acting on a charged particle per unit charge is called electric field. It is given by :

q is the charge on electron

E = 20000 N
(b) The V is the potential difference between the plates. The relation between the potential difference and the electric field is given by :


V = 4200 volts
Hence, this is the required solution.