Chronology | Current Month | Current Thread | Current Date |
[Year List] [Month List (current year)] | [Date Index] [Thread Index] | [Thread Prev] [Thread Next] | [Date Prev] [Date Next] |
This means in order to find the E inside a capacitor you have to haveone
end of the gaussian surface inside the gap . . . The location of thefar end would either be inside one plate
or outside the capacitor. At this point you need additionalinformation.
If the far end is inside a plate then you need to know all the charge ison
the inner surface of that plate.
Okay. It took me a while... but now I get what Bob Sciamanda did to getthe
some of the algebra I said I didn't understand. He is using the
superposition principle to find fields in various places in and around
parallel-plate capacitor. I thought he was using Gauss' Law.that's
Of course the reason I thought he was using Gauss' Law was because
the way Ludwick posed the original question, and that's the way I wrotemy
original response to Ludwick. I said, and I maintain, solving for thefield
inside a capacitor using Gauss' Law (and nothing else) is not obvious.Gauss'
In my understanding, using the superposition principle is not using
Law. Using GL to find the field at a spot means (1) knowing what thenet
charge is inside an appropriate gaussian surface, (2) having the pointof
interest reside at an appropriate place on some portion of that gaussianelectric
surface, (3) finding the flux through that portion of the surface using
Gauss' Law, (4) using the flux and area and symmetry to deduce the
field at that point.one
This means in order to find the E inside a capacitor you have to have
end of the gaussian surface inside the gap. A wise choice of surfacewould
dictate this portion of the surface is flat and parallel to the plates.perpendicular
Another wise choice would make the other parts of the surface
to the plates except for the far end. The far end also be flat andparallel
to the plates. The location of the far end would either be inside oneplate
or outside the capacitor. At this point you need additionalinformation.
If the far end is inside a plate then you need to know all the charge ison
the inner surface of that plate. If the far end is outside thecapacitor
then you need to know the field there is zero. If you don't know one ofthis
these things you can't calculate the field in the capacitor gap using
method, i.e. using Gauss' Law. And... I don't see how you can showeither
of these things using Gauss' Law. Yes, you can show these using thethe
superposition principle. But I thought that was not allowed. I thought
question was, "Can you calculate the field using Gauss' Law?"419-358-3270
Michael D. Edmiston, Ph.D. Phone/voice-mail:
Professor of Chemistry & Physics FAX:419-358-3323
Chairman, Science Department E-Mailedmiston@bluffton.edu
Bluffton College
280 West College Avenue
Bluffton, OH 45817