Physics II / Magnetic Materials
Practice question · Fill in the blanks

Complete the description of how the two auxiliary fields parallel one another.

In a dielectric the displacement field hides the ______ charge so that Gauss’s law counts only free charge. In a magnetic material the ______ field plays the same role, hiding the bound ______ so that Ampère’s law counts only free ______.

Word bank: bound · auxiliary H · currents · current · polarisation

Hints
  1. Each auxiliary field exists to remove the bound sources from its law.
  2. In magnetism the bound sources are circulating currents, not charges.
Show the answer

In a dielectric the displacement field hides the bound charge so that Gauss’s law counts only free charge. In a magnetic material the auxiliary H field plays the same role, hiding the bound currents so that Ampère’s law counts only free current.

Why

D\mathbf{D} removes bound charge from Gauss’s law and H\mathbf{H} removes bound current from Ampère’s law. Both are bookkeeping devices, and in both cases the force is still exerted by the original field.

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