AP Physics C — Magnetic Field inside and outside a coaxial cable

A Coaxial Cable is a cord that has an inner and outer conductor separated by an insulating medium. The conductors carry current in opposite directions.

For the coaxial cable with inner conductor radius and current , conductor radius , and outer conductor radius and current :

What is the magnitude of the magnetic field at a distance from the axis of the cable when , when , and when ?

When :

When :

When :

The current from both conductors cancel out since they move in opposite directions.