Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: New theorem of classical electromagnetism: equilibrium magnetic field
  and current density are zero inside ideal conductors   We prove a theorem on the magnetic energy minimum in a system of perfect, or
ideal, conductors. It is analogous to Thomson's theorem on the equilibrium
electric field and charge distribution in a system of conductors. We first
prove Thomson's theorem using a variational principle. Our new theorem is then
derived by similar methods. We find that magnetic energy is minimized when the
current distribution is a surface current density with zero interior magnetic
field; perfect conductors are perfectly diamagnetic. The results agree with
currents in superconductors being confined near the surface. The theorem
implies a generalized force that expels current and magnetic field from the
interior of a conductor that loses its resistivity. Examples of solutions that
obey the theorem are presented.

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The categories of this paper are: chem-ph
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The categories of this paper are: hep-ex
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The categories of this paper are: stat
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The categories of this paper are: q-fin
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The categories of this paper are: quant-ph
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The categories of this paper are: econ
7
The categories of this paper are: hep-th
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The categories of this paper are: adap-org
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The categories of this paper are: gr-qc
15
The categories of this paper are: nucl-ex
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The categories of this paper are: solv-int
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The categories of this paper are: atom-ph
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The categories of this paper are: astro-ph
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The categories of this paper are: hep-lat
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The categories of this paper are: eess
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The categories of this paper are: comp-gas