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[Phys-l] Kirchhoff's laws, or not (was: arcing ...)



Teaching about Kirchhoff's laws is a standard part of
the introductory physics curriculum.

According to
http://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws
"Both circuit rules can be directly derived from Maxwell's equations"

... but alas this is not true. Both of Kirchhoff's laws
are flatly contradicted by the Maxwell equations, and
both are routinely violated in practice.

1) The video we discussed yesterday shows a gross
violation of K's current law. At any given moment,
current is flowing into the helicopter node but not
flowing out.
>> http://www.youtube.com/watch?v=9tzga6qAaBA

Other examples abound.

2) Ground loops are a familiar example of a gross
violation of K's voltage law.

This is important in the real world. Anybody who does
any kind of low-noise instrumentation probably needs
to deal with violations of Kirchhoff's laws on a daily
basis. This includes physics-lab instrumentation as
well as other stuff such as medical instrumentation.

There's a lot more that could be said about this if
anybody's interested.