Question

Find the electric force experienced by a charge reduced to a unit area of an arbitrary conductor if the surface density of the charge equals σ.

Answer 1

Near the conductor  

This field can be written as the sum of two parts E₁ and E₂. E₁ is the electric field due to an infinitesimal area dS.

The remaining part contributes  both sides. In calculating the force on the element dS we drop E₁ (because it is a self-force.) Thus