Electromagnetic field theory - wykład

Electromagnetic fi eld theory There are, however, situations when the assumptions of neither distributed circuit theory
nor lumped circuit theory are applicable. In these contexts we are obliged to deal directly
in terms of the electromagnetic fields.
The need for field theory can come about for several reasons. One is that we are not
sure just where the currents flow. They may still be on conductors, but the conductors
are no longer filamentary, and we may have more current on one part of a conductor than
another, and we are not sure by how much.
Secondly the magnetic flux density distribution may be such that it does not arrange
itself in planes. Thirdly the displacement current may be comparable with the conduction
current in the same region. There may even be no conduction current, and the magnetic
field may be created purely by displacement current. This is exactly what happens in
electromagnetic wave propagation.
When any of these things occurs we generally need the full field solution as discussed
in Chapters 8 to 11.
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