Re: inductor circuit concept

[SSHS KPHOX <kphox@MAIL.CCSD.K12.CO.US>]

PHYS-L@lists.nau.edu writes:
> Having done that, the potential difference across a
> resistor is *always* -iR when one "goes with the flow" and +iR
> when one "goes against the flow."  This seems natural because of
> the obvious and proper analogy with a stream as implied by the
> words.
>
> In exactly the same way, the potential difference across an
> inductor is *always* -Ldi/dt when one "goes with the flow" and
> +Ldi/dt when one "goes against the flow."

I want to thank all who replied.

The -iR is easy as it is a potential drop in the direction of the current.
The idea of calling the potential across the inductor as always -Ldi/dt
when trasversing in the direction of the flow is far less intuitive. It is
so clearly a potential gain in the decay circuit that I have a hard time
writing a negative. It does work and I recognize the fact that the -di/dt
makes the term positive ( which is how I made the derivation work in class
on Friday) but it seems more like memorizing a rule than not.

I will continue to ponder and remain grateful for all the help I get here.

Thanks

Ken Fox
AP/IB Physics Teacher
Smoky Hill High School
Aurora, CO