Question

Electric field close to plane of charge is shown in figure. External electric field in V/m is

Answer 1

let external field be $E_o$
$E_1=E_o+\frac{\sigma }{2{ϵ}_o}=20$ --(1)
$E_2=\frac{\sigma }{2{ϵ}_o}-E_o=5$ --(2)
By (1) - (2) $E_o$ = 7.5