Here's a circuit where the switch has been closed for a long time, so that Vc(t) is fully charged. At t=0 the switch opens. R1=R2.
When doing the transient analysis for what happens when t>0:
I would assume the the current goes in a clockwise direction in the loop betwen the capacitor and the resistance R2. Then we can write a KVL equation for this as
-Vc(t) + VR2 = 0
(since Vc(t) = VR2)
Which eventually (with diff.eq) gives the solution Vc(t)=Vo/2*e^(t/RC)
However this solution is incorrect because that would be an increasing voltage. But if we instead assume that the current goes COUNTERCLOCKWISE between Vc and R2, the solution becomes correct, since then we have
Vc(t) + Vr2 = 0
Which (eventually) gives the correct solution Vc(t)=Vo/2*e^-(t/RC)
But why is this correct? Doesn't the current actually go clockwise? Why does the solution become correct if we assume it to go counterclockwise which is not true?
Someone please explain!
When doing the transient analysis for what happens when t>0:
I would assume the the current goes in a clockwise direction in the loop betwen the capacitor and the resistance R2. Then we can write a KVL equation for this as
-Vc(t) + VR2 = 0
(since Vc(t) = VR2)
Which eventually (with diff.eq) gives the solution Vc(t)=Vo/2*e^(t/RC)
However this solution is incorrect because that would be an increasing voltage. But if we instead assume that the current goes COUNTERCLOCKWISE between Vc and R2, the solution becomes correct, since then we have
Vc(t) + Vr2 = 0
Which (eventually) gives the correct solution Vc(t)=Vo/2*e^-(t/RC)
But why is this correct? Doesn't the current actually go clockwise? Why does the solution become correct if we assume it to go counterclockwise which is not true?
Someone please explain!
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