Suppose the field inside a large piece of magnetic material is B0, so that H0 = (1/?0)B0 ?? M.

(a) Now a small spherical cavity is hollowed out of the material (Fig. 6.21). Find the field at the center of the cavity, in terms of B 0 and M. Also find H at the center of the cavity, in terms of H0 and M.

(b) Do the same for a long needle-shaped cavity ranning parallel to M.

(c) Do the same for a thin wafer-shaped cavity perpendicular to M. Assume the cavities are small enough so that M, B0, and H0 are essentially constant. Compare Prob.4.16.

(a) Sphere (b) Needle (c) Wafer M