What is the Magnetic Field Inside a Cylindrical Coaxial Cable?

[Floriane Houenagnon]

Homework Statement

A portion of along,cylindrical coaxialcable is shown in the accompanying figure. A current I flows down the center conductor, and this current is returned in the outer conductor. Determine the magnetic field in the regions (a) r ≤r1, (b) r2 ≥r ≥r1, (c) r3 ≥r ≥r2, and (d) r ≥r3. Assume that the current is distributed uniformly over the cross sections of the two parts of the cable.

Relevant Equations

B∫dl = μI

Inner current = I1
Outer Current = I2

I = J*A
J = Current Density
A = Area

I have no idea where to start.

 

[quinoa19]

The problem is a straightforward application of Ampere's law:

(the magnetic field on the loop) x (loop length) = (permeability) x (total current inside the loop)

Try solving it first for only 1 wire with radius r1 and current I1 for r>r1.