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Re: [Phys-l] RC Disharge Analysis



Michael Edmiston wrote:
Well John, the reason I didn't draw any diagrams is because your ASCII drawings always come across virtually worthless on my screen, so I figure it isn't worth the effort to try to draw a diagram for sending through PHYS-L. I can't make out anything from the "diagrams" in your posts.

1) The diagrams look fine in the archives, e.g.
https://carnot.physics.buffalo.edu/archives/2006/02_2006/msg00362.html
https://carnot.physics.buffalo.edu/archives/2006/02_2006/msg00363.html

2) The diagrams returned to me, as quoted by M.E., are fine; the
have obviously not sustained any permanent damage.

3) Try viewing your mail with a fixed-width font.

The circuit is in virutally every calculus-based physics book.

Nevertheless, there are two ways of drawing the circuit,
which naturally suggest different sign conventions for the
intermediate results ... but of course representing the same
physics and producing the same final results.

... say I = dq/dt which is the standard definition of current.

Standard??? The laws of nature trump the alleged standard.

There are conflicting conventions here.

a) Take any two-terminal device (notably including resistors and
capacitors) and let the voltage across it be V. Without loss
of generality label the terminals A and B such that V = V_A - V_B.
Then by convention, the current flows into terminal A and flows out
of terminal B.

b) Kirchhoff's loop law requires the current to flow the same way
(e.g. "clockwise") through all elements.

In the version that M.E. suggests, these two conventions conflict.
Something's got to give. Pick one element, reverse the convention,
and accordingly reverse the sign in the corresponding equation.