 1
 0
 Homework Statement
 Prove that Ampere's law ( ∮ B dl = mu_0 x enclosed current ) can be rewritten in terms of free currents only like this : ∮ (1/mu_r) B dl = mu_0 x free enclosed current where mu_r is the relative permeability of the material.
 Homework Equations

Ampere's law : ∮ B dl = mu_0 x enclosed current
Ampere's law rewritten : ∮ (1/mu_r) B dl = mu_0 x free enclosed current
This is not really the assignment of my homework ( my assignment require me to find the magnetic field inside a small air gap on a toroide magnet wrapped with N turns of a wire that carry a current I ) . I'm at some point in the solution where I kind of need to use the rewritten Ampere's law to continue but I can't use it unless I prove it because it has not been proven in class. I couldn't find the proof anywhere so I was hoping to find a little help here !