Consider an arbitrary shaped conductor at any point at which local charge density is $3\mathrm{nC}/{\mathrm{m}}^2$. The electric force  per unit area experienced by the conductor in the vicinity of specified point is

Consider the situation as illustrated in diagram. The electric force experienced by conductor per unit area is 

given by, $F=\frac{{\sigma }^2}{2{ϵ}_0}$ where $\sigma$ is local charge density. 

This term is also known as electric pressure. 

$\begin{array}{l}F=\frac{{\left(3\times {10}^{-9}\right)}^2}{2\times 8.85\times {10}^{-12}}\mathrm{N}/{\mathrm{m}}^2\\ =5.08\times {10}^{-7}\mathrm{N}/{\mathrm{m}}^2=0.51\mu \mathrm{N}/{\mathrm{m}}^2\end{array}$