Correct Answer - D
d. `E = sigma/(2epsilon_0)`
`F = E dr = (sigma d A sigma)/(2epsilon_0)`
`P = F/(dA) = sigma^2/(2epsilon_0)`
`Force = PpiR^2 = sigma^2/(2epsilon_0)piR^2`
`=Q^2/(16pi^2R^4) (piR^2)/(2epsilon_0) = Q^2/(32piepsilon_0R^2)`
`= ((20 xx 10^(-6)) xx 9 xx 10^(9))/(8(1.5 xx 10^(-2))^2) = 2000N`.