# RLC Parallel Circuit Analysis

#### zorro_phu

Joined Jun 14, 2018
20
I forgot to mention, why capacitor voltage is 0v at t=0-. Is not the voltage of resistor = voltage of capacitor(t<0) since they are in parallel?

#### WBahn

Joined Mar 31, 2012
25,096
The solution is probably either for an earlier version of the the problem or the person doing it didn't read the schematic closely enough.

#### MrAl

Joined Jun 17, 2014
6,966
I forgot to mention, why capacitor voltage is 0v at t=0-. Is not the voltage of resistor = voltage of capacitor(t<0) since they are in parallel?
Hello there,

Are you using the schematic drawn there?
If so, where are you getting -5ua from?
The cap voltage is not 0v at t=0.

#### WBahn

Joined Mar 31, 2012
25,096
Hello there,

Are you using the schematic drawn there?
If so, where are you getting -5ua from?
The cap voltage is not 0v at t=0.
If I'm reading his original post correctly, he is saying that the solution provided is claiming that the initial inductor current (at t = 0-) is 5 uA. That is the main thing he is questioning. Similarly, I think the solution is saying that the initial cap voltage is zero and he is questioning that.

I haven't looked at his entire solution, but I took a quick look at his initial conditions and I think he got them right.

#### MrAl

Joined Jun 17, 2014
6,966
If I'm reading his original post correctly, he is saying that the solution provided is claiming that the initial inductor current (at t = 0-) is 5 uA. That is the main thing he is questioning. Similarly, I think the solution is saying that the initial cap voltage is zero and he is questioning that.

I haven't looked at his entire solution, but I took a quick look at his initial conditions and I think he got them right.
Hi,

Oh i thought i saw that he found the current source to be -5ua but maybe i read that wrong.
Yes i agree it is 5ua up until t=0 and then it goes to zero, but before that the cap must have charged up to some degree which puts a voltage across it.
[LATER]
I went back and looked at his work and he has -5ua written and then that produces what he wrote as Vc=-1uv, which is not correct.

Just for a point of verification, i got a peak current in the inductor of between 0.5 and 0.6 amps but i used R=1, C=1, L=1, and Vc(0)=1. If he wants to redo the problem with those values, he should be able to find that result within those bounds.

#### WBahn

Joined Mar 31, 2012
25,096
I went back and looked at his work and he has -5ua written and then that produces what he wrote as Vc=-1uv, which is not correct.
I agree with you. His cap voltage is consistent with the current he has in his diagram, but that current is not correct relative to the problem statement.