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]

Re: [Phys-l] RC Discharge



I also agree with all four of Bob's diagrams. However, please note that the thing that got me off on this was my son asking about Serway/Jewitt. The Serway/Jewitt diagram is *exactly* Bob's third diagram. (Same capacitor placement, same resistor placement, same +/- signs on capacitor, same current arrow.) But the Serway analysis is -q/C - IR = 0 and I = +dq/dt.

If we agree that Bob's analysis of his third circuit is correct, then the Serway/Jewitt analysis would certainly seem incorrect. Can anyone look at Bob's third diagram and legitimize the Serway/Jewitt analysis?

I also think Tim Folkert's comment about the q in dq/dt is helpful. Students are clearly thinking dq/dt means charge moving past a point in a wire. They are not thinking of dq/dt as the rate of change of charge on the capacitor. Making this clear should help them.



Michael D. Edmiston, Ph.D.
Professor of Physics and Chemistry
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu