Fundamentals of Engineering Electromagnetics 1st Edition by David Cheng

Exercise 17

A long, round wire of radius a and conductivity is coated with a material of conductivity 0.1
a) What must be the thickness of the coating so that the resistance per unit length of the uncoated wire is reduced by 50%
b) Assuming a total current I in the coated wire, find J and E in both the core and the coating material.