Consider a cylindrical wire of radius R (indefinitely long) that
carries a total steady current I such that there is a constant
current density j across the profile of the wire (for the first
part of this task, consider just a current density in vacuum)
a) in order to calculate the magnetic induction it is suitable
to work in cylindrical coordinates. Considering Boundary conditions
at ρ→∞, the magnetic induction ca be written as B=B_ρ (ρ,φ,z) e_ ρ
+ B_ φ(ρ,φ,z)e_...