A co-axial cable consists of a thin inner current carrying conductor fixed along the axis of a hollow current carrying conductor. Let B₁ and B₂ be the magnetic fields in the region between the conductors and outside the conductor, respectively

${\mathrm{B}}_1\ne 0,{\mathrm{B}}_2\ne 0$ for conductors carrying equal currents in opposite directions

B₁ = B₂ for conductors carrying equal currents in same directions at distances x and 2x from the axis respectively.

${\mathrm{B}}_1\ne 0,{\mathrm{B}}_2=0$ For conductors carrying equal currents in opposite directions

${\mathrm{B}}_1\ne 0,{\mathrm{B}}_2\ne 0$ for conductors carrying equal currents in the same direction