Why the electric field at the outer surface of a hollow charged conductor is normal to the surface?

Show that the electric field at the surface of a charged conductor is proportional to the surface charge density.

The electric field intensity at the surface of a charged conductor is

Why must electrostatic field at the surface of a charged conductor be normal to the surface at every point ? Give reason.

The electric field intensity on the surface of a charged conductor is

Why the surface of an isolated charged conductor is an equipotential surface ?

Why electric fields just outside the surface of a conductor is perpendicular to the surface?

Obtain an expression for electric field at the surface of a charged conductor.