A closed path containing a magnetic flux. The path is clearly delimited only if it consists mainly or wholly of ferromagnetic or other good magnetic materials; examples include transformer cores and iron parts in electrical machines. The design of these parts can often be assisted by analogy with electrical circuits, treating the magnetomotive force as the analogue of e.m.f., the magnetic flux as current, and the reluctance as resistance. There is, however, no actual flow around a magnetic circuit.