3.3 Merits of Introducing Superconductivity
41
Fig. 3.11 Current and
internal magnetic flux
density when a longitudinal
magnetic flux density is
applied to a hollow
cylindrical superconductor
hollow region is completely shielded. On the other hand, the magnetic moment inside
the magnetic material is expressed as an assembly of small magnetizing current loops,
as shown in Fig. 3.12a. Since these currents cancel out between adjacent loops, the
magnetizing current remains also on the inner surface (see Fig. 3.10b). Thus, the
magnetic flux density appears in the hollow region without being shielded.
The above comparisons clearly show the analogy between the electric and
magnetic phenomena. That is, the difference between the electric charge and the
polarization charge is analogous to that between the current and the magnetizing
current. Hence, it can be said that the introduction of a superconductor is effective
to show this example.
Fig. 3.12 a Internal magnetizing current loops and b the resultant magnetizing current remaining
on the surfaces and the magnetic flux density in the hollow center when a longitudinal magnetic
flux density is applied to a hollow cylinder of magnetic material