# First order RC, RL specific question

#### Themanslayer

Joined Dec 4, 2012
1
Hey guys, I am wondering if one of you can help me answer this question. I have a final today and I would appreciate any effort to help.

Let me briefly explain what I already know:

• Given a RC, RL circuit with multiple caps or inductors they can be reduced to find the L eq or C eq values.

• When finding Tau you must use Req and C eq or L eq values.

My question is if the problem wants you to find the voltage across a specific cap or inductor, would I reduce the circuit to its C eq or L eq before finding the initial voltage (V(0-)) or leave it alone?

#### tshuck

Joined Oct 18, 2012
3,534
it would depend on the layout of the circuit. If you have the voltage across two series capacitors, and you need to find one, then, then voltage will not be the equivalent voltage across Ceq. If, however, there are two capacitors in parallel, then the voltage across Ceq would be the voltage across both capacitors...

It is possible that you could get a circuit that has one capacitor initially charged and another that is not, which is connected at t=0...