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Re: [Phys-l] RC Discharge






I agree that Serway's lucidity is woefully wanting. From your description
I
would say that the upward arrow at R is meant to show the direction defined
as a positive PD across R, implying a CW direction for positive i. With
the
lower capacitor plate defined as carrying q, then a CW loop would directly
give: -q/C - iR = 0.


Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
http://www.winbeam.com/~trebor/
trebor@winbeam.com
| ----- Original Message -----
| From: "Michael Edmiston" <edmiston@bluffton.edu>
| To: "Bob Sciamanda" <trebor@winbeam.com>; "PHYS-L Maillist"
| <phys-l@carnot.physics.buffalo.edu>
| Sent: Sunday, February 19, 2006 11:22 AM
| Subject: Re: [Phys-l] RC Disharge Analysis
|
|
|| Bob S. said, "[Serway] is correct if i is defined as positive when it is
|| CW (in your previously drawn circuit), and q is the charge on the lower
|| plate. Note this also defines the relation i = dq/dt."
||
|| I agree we can say we are choosing I as positive when positive charges
|| are moving clockwise. But that is not the figure in the the Serway
|| text. Serway has the capacitor on the left with positive plate down.
|| The resistor is on the right with current arrow pointing up (i.e.
|| current is assumed, by Serway, as CCW). Serway says -q/C - IR = 0.
|| That means he applied the loop theorem traversing the capacitor from
|| bottom to top (CW loop) and he traversed the resistor from bottom to top
|| (CCW loop). He switched his loop direction when he applied the loop
|| theorem.
||
|| Michael D. Edmiston, Ph.D.
|| Professor of Physics and Chemistry
|| Bluffton University
|| Bluffton, OH 45817
|| (419)-358-3270
|| edmiston@bluffton.edu
||
||
||
|