Magnetic field inside coaxial conductor

[Shukie]

Homework Statement

The problem asks us to find the magnetic field inside a coaxial conductor that consists of an aluminum wire of radius r1 surrounded by a cylindrical aluminum shell of inner radius r2 and outer radius r3. I know how to do this, but it also says that there is oil flowing between r1 and r2 to carry away heat. Does this change anything about the direction and/or magnitude of the magnetic field?

 

[supratim1]

the oil will have a different value of magnetic permeability, which you must take into account.