A rectangular bar magnet is uniformly magnetised along its length
PHYSICS · Subjective · Fermi University Physics · Electricity, Magnetism & Electromagnetism · Magnetostatics · Magnetic materials
Electricity, Magnetism and Electromagnetism, Ch Magnetisation, bound currents and the auxiliary field H
Problem
A rectangular bar magnet is uniformly magnetised along its length, from its south end towards its north end. There is no winding and no free current anywhere. A three-panel figure is to be drawn, in a plane containing the magnet's long axis: one panel for B, one for H and one for M. Six candidate patterns, P1 to P6, are described; each is what one panel might show. P1 Lines forming closed loops, which inside the material run from the north end to the south end and outside run from the south end round to the north end. P2 Uniform arrows inside the material only, all of equal length, pointing from the south end towards the north end; nothing outside. P3 Lines that begin on the north end face, run out through the surrounding space to the south end face, and inside the material run from the north end to the south end. P4 Lines forming closed loops, which inside the material run from the south end to the north end and outside run from the north end round to the south end. P5 Uniform arrows inside the material only, all of equal length, pointing from the north end towards the south end; nothing outside. P6 Zero everywhere. Choose the pattern for each panel, and name in each case the law or definition that decides it. (a) The B panel. (b) The H panel. (c) The M panel.