A very long solid cylinder with radius R has positive chargeuniformly distributed throughout it, with charge per unit volume ? . a) Derive the expression for the electric field inside the volume a distance r from the axis of the cylinder interms of the charge density. b) What is the electric field at a point outside the volume in terms of the charge per unit length ? in the cylinder? c) Compare the answers to parts (a) and (b) for r=R. d) Graph the electric field magnitude as a function of r from r=0 to r=3R.