- #1
popo902
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Homework Statement
A security alarm for an office building door is modeled by the circuit [below]. The switch represents the door interlock, and v is the alarm indicator voltage. Find v(t) for t>0 for the circuit [below]. The switch has been closed for a long time at t=0-
http://i36.photobucket.com/albums/e47/jo860/img014.jpg
Homework Equations
V = L di/dt
The Attempt at a Solution
ok so, i see that it has been closed for a long time, which must mean the inductor is "charged" and at steady state at t=0-, t=0+, and i think also t=0 since current cannot change instantaneously
I used mesh analysis and found the current "stored" in the inductor to be 2A
then i see that when the switch is opened, it splits the circuit into two circuits...right?
so then only the left side is where i work.
then the inductor would sort of be like a finite current source pumping current through the 9 then 3 ohm resistor--the opposite way the previous current was going(is this correct?)
I see it like if i find the current through the inductor at t>0, then i just multiply that by 9 to get the voltage across 9
could someone maybe give me a hint to what I'm missing or if I'm wrong?
would it right to use KVL?