# Magnetic field around a wire ?

by cragar
Tags: field, magnetic, wire
 P: 2,468 Lets say we have an infinite current carrying wire and it is wrapped with a dielectric materiel. Lets say the dielectric is 1 cm in diameter around the wire. But lets say I want to find the B field when Im outside the dielectric, Could I just use amperes law . And when im inside the dielectric I would use the H field and then get B by using the magnetic susceptibility of the material . Is this correct .
 Sci Advisor PF Gold P: 1,777 Off the top of my head I think you can just use the standard magnetic field equation for an infinite wire. The boundary conditions require that the tangential H field be continuous. Since the B field will be described as $$\mathbf{B}(\rho) = \frac{\mu I}{2\pi\rho} \hat{\phi}$$ Since the fields are tangential to the inhomogeneity they will not be affected since they will automatically have continous H fields. So this is situation where Ampere's Law will give the correct result.
 P: 2,468 Thanks for your response , ok what if i wrapped a superconductor around the wire and cooled it with liquid nitrogen . And lets say the superconductor goes 1 cm around the wire . Outside the superconductor the B field would be zero , Would amperes law still work?