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inductor circuit concept



I have a loop theorem question for an inductive circuit. Maybe someone can
clarify it for me.

When activating a RL circuit with battery and switch loop theorem gives:

emf - iR - L(di/dt) = 0 form this we get i = (emf/R)(1-e^t/timeconstant)

when allowing to decay, I want to write the loop theorem as:
-iR + L(di/dt) = 0 as there is a potential drop across the resistor and
gain in the inductor. This makes it hard to get a negative exponent in the
current equation.
The text says we can use the original equation and set emf to zero. This
works algebraically but does not set well with my concept of energy
conservation. I know that di/dt is negative which will make the term
positive but .....I also know that the self induced emf is -Ldi/dt which
could make a problem in the first equation.

I need help reconciling the algebraic signs here with my concept of
incresing and decreasing potentials as I traverse a loop.

Thanks

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