# Homework Help: Finding current in a RLC circuit using kirchhoff laws

1. Apr 10, 2012

### karlis123

1. The problem statement, all variables and given/known data

Find current flowing through E1 ( find I1).

2. Relevant equations

I see 6 currents, atleast until the capacitor is charged, what i find confusing are the branches without any resistance and they seem to mess up my equations.

3. The attempt at a solution
1st kirchhoff's law
I1+I5=I2
I3+I6=I1
I6+I5=I4
2nd kirchhoff's law
I2*L-I3*C=E1
I2*L+R1*I5=E2
I3*C+I6*R2=0

In the end i get 2*I5-I6=5 which doesn't solve anything for me so I guess I'm still missing something there.
Its been some time since I've done circuit calculations any help would be apritiated

#### Attached Files:

• ###### IMG_9883.jpg
File size:
12 KB
Views:
189
2. Apr 10, 2012

### Staff: Mentor

Are you after a steady-state DC analysis, or is this AC?

If DC, then the inductor and capacitor can be replaced by a short-circuit and an open-circuit, resp.

3. Apr 10, 2012

### karlis123

its a dc circuit right after commutation, the commutator switch is closed and is in series with E2 and R1 (i replaced it with a black line in the picture).
Here i found an example, as i understand i have to calculate the currents in the exact moment when the condenser is being charged.
any help with the equations would help allot.

#### Attached Files:

• ###### example.png
File size:
33.1 KB
Views:
187
Last edited: Apr 10, 2012
4. Apr 10, 2012

### Staff: Mentor

E1 and R1 don't appear to be connected in your circuit. So where is this commutator?

5. Apr 10, 2012

### karlis123

ow my bad! E2 I ment

6. Apr 10, 2012

### Staff: Mentor

So to be clear, the circuit looks like this?

#### Attached Files:

• ###### Fig1.gif
File size:
2.7 KB
Views:
241
7. Apr 10, 2012

exactly