Demagnetizing Force.-It has already been mentioned that when a ferromagnetic body is placed in a magnetic field, the resultant magnetic force H, at a point within the body, is compounded of the force H o, due to the external field, and of another force, Hi, arising from the induced magnetization of the body.
Except in the few special cases when a uniform external field produces uniform magnetization, the value of the demagnetizing force cannot be calculated, and an exact determination of the actual magnetic force within the body is therefore impossible.
Since I =KH, we have KH I-KNI =KHo, (30) or H =Ho-NI, NI being the demagnetizing force H i.
Du Bois (Magnetic Circuit, p. 33), the demagnetizing factor, and the ratio of the length of the ellipsoid 2c to its equatorial diameter 2a (=c/a), the dimensional ratio, denoted by the symbol nt.
The demagnetizing force inside a cylindrical rod placed longitudinally in a uniform field Ho is not uniform, being greatest at the ends and least in the middle part.