What you’re describing is magnetic shielding. If we ignore end effects – where the wire enters the Fe cylinder – external B fields will not produce a force on the wire, but will cause realignment of the Fe atomic spins on the surface of the cylinder. ….. in theory. Robert If a single conductor is enclosed in an iron cylinder, such that all the field is enclosed within the magnetic material. will the motive force of external fields still apply? Like as with the twin conductors of the above definition, for example.. Philip.