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Dec4-10, 04:23 PM
P: 1,036
Quote Quote by DaleSpam View Post
Where you said that "KVL only holds when no time changing mag fields are present". In an inductor there is a time changing magnetic field, but KVL does just fine with inductors.

A capacitor does not have a net charge.
I meant time varying fields present in the circuit loop. Time varying fields on the interior of the inductor is modeled by circuit theory, w/o the need to consider fields. The Lewin paper explicitly stated the field inside the circuit loop, not that on the interior of an inductor. Did you read the paper by Dr. Lewin?

As far as a cap having " no net charge", this is very semantical. "Charge" as used by the science community implies "differential". An "uncharged cap" has lots of charge, but zero difference. A "charged cap" has the same total absolute charge but is displaced forming a differential. If you define "net charge" as total charge on both plates, then of course there is no "net charge" in either case, energized or not.

Whan I say "charge" in ref to a cap, I infer the differential quantity, not the absolute total which you define as "net charge".

Dr. Lewin is correct on all counts. He simply illustrated how non-conservative fields differ from conservative. You're trying to look for reasons to poke holes in his case by bringing in arbitrary arguments based on your own semantics. In the final analysis Dr. Lewin states the following.

1) With conservative E fields, KVL holds, & the potential from a to b is independent of the path.

2) With non-conservative E fields, KVL does not hold, & the potential from a to b is dependent on the path.

Introducing hyperbole does not alter this basic tenet. Is there any issue with the above 2 statements?