A spherical conductor of radius R carries a total charge Q.
(a) Show that the magnitude of the electric field just outside the sphere is E = σ/ϵ0, where s is the charge per unit area on the conductor's surface.
(b) Construct an argument to show why the electric field at a point P just outside any conductor in electrostatic equilibrium has magnitude E = σs/ϵ0, where s is the local surface charge density.