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DemagnetizationEllipsoidally shaped magnets sustain uniform magnetization parallel to their principal axes. Let us call {$B_m, M, H_m$} the induction, magnetization and magnetic field inside the magnet, and {$B_o, H_o$} the induction and magnetic field outside the magnet, far form it, assuming that both are again uniform in these conditions. The demagnetization factor {$0\le N \le 1$} is defined by the relation between {$H_m$} and {$H_o$} {$ H_m=H_o-NM$} Hence {$ B_m=\mu_0(H_m+M) = \mu_0 [H_o + (1-N)M] $} The infininite cylinder has N=0 for the field parallel to its axis, and {$N=\frac 1 2$}, for the field perpendicular to its axis. The sphere has {$N=\frac 1 3$}. The infinite slab has {$N=0$} for field in its plane, and {$N=1$} for field perpendicular to it. As a consequence in this last case the internal induction is {$B_m=\mu_0H_o=B_o$}. |