| I = κH = | κH0 | = | 3κ | H0, |
| 1 + 4⁄3πκ | 3 + 4πκ |
(32)
Whence
| H = | 3 | H0 = | 3 | H0, |
| 3 + 4πκ | μ + 2 |
(33)
and
| B = μH = | 3μ | H0. |
| μ + 2 |
(34)
Equations (33) and (34) show that when, as is generally the case with ferromagnetic substances, the value of μ is considerable, the resultant magnetic force is only a small fraction of the external force, while the numerical value of the induction is approximately three times that of the external force, and nearly independent of the permeability. The demagnetizing force inside a cylindrical rod placed longitudinally in a uniform field H0 is not uniform, being greatest at the ends and least in the middle part. Denoting its mean value by Hi, and that of the demagnetizing factor by N, we have
H = H0 − Hi = H0 − NI.