Chapter 12, Problem 85AP

, A ray long, thick, cylindrical wire of radius R carries a current density J that varies across its cross-section, The magnitude of the current density⁷ at a point a distance r from the center of the wine is given by $J=J_0\frac{r}{R}$ where $J_0$ is a constant. Find the magnetic field (a) at a point outside the wire and (b) at a point inside the wire. Write your answer in terms of the net current I through the wire.