Last Week's Question

metal sheets

At the surface of a perfect conductor,

  1. the normal component of the electric field is zero
  2. the tangential component of the electric field is zero
  3. the tangential component of the magnetic field is zero
  4. all of the above

Answer

The correct answer is "b". This is why the electric field probes used to monitor radiated immunity tests should never be parallel to a nearby metal surface. The field near the surface will be much lower than the fields farther from the surface.

The normal component of the magnetic field will also be zero at frequencies other than D.C. for perfect conductors. For good conductors, like copper or aluminum, the normal component of the magnetic field will be zero at frequencies above several kHz (depending on the thickness of the conductor).

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