Magnetic Field inside and outside wire

[Chip90]

Homework Statement

There is a wire with current I ,charge density j, and radius R. Find the Magnetic Field outside the wire (a>r) and inside the wire (a<r).

Homework Equations

Biot- Savart or Amperes law

I=JdotA

The Attempt at a Solution

Not sure how to attempt it or which equation to use. From my previous question about solenoids, I know that Magnetic Field only depends on length of L, not radius of wire..

 

[Mindscrape]

Once you are inside the wire the total current depends on r in the way that you are still adding in more current to your amperian loop as you slowly go through the wire. Once you leave the wire, the amount of current enclosed in the amperian loop stays the same, and so the current does not depend on r in this case.

 

[Chip90]

ok so to find the inner B field, I use

which would lead me to say

B=Uo*I/ 2*pi*r

and for the outer

B=Uo*I/L