a low permeability, while the other one has a very high one. We
will violate Faraday’s law unless the component of theHfield par-
allel to the boundary is a continuous function,H‖,1=H‖,2. This
means that ifμ/μois very high, the component ofB=μHpar-
allel to the surface will have an abrupt discontinuity, being much
stronger inside the high-permeability material. The result is that
when a magnetic field enters a high-permeability material, it tends
to twist abruptly to one side, and the pattern of the field tends to
be channeled through the material like water through a funnel. In
a transformer, a permeable core functions to channel more of the
magnetic flux from the input coil to the output coil. Figure j shows
another example, in which the effect is to shield the interior of the
sphere from the externally imposed field. Special high-permeability
alloys, with trade names like Mu-Metal, are sold for this purpose.
j/A hollow sphere withμ/μo = 10, is immersed in a uniform, externally imposed magnetic field. The
interior of the sphere is shielded from the field. The arrows map the magnetic fieldB. (See homework problem
47, page 755.)Section 11.7 Electromagnetic properties of materials 741