# Kirchhoff's circuit laws

1. Feb 20, 2008

### Bob Loblaw

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

Find the unknown emf and the unknown currents in the circuit below, in which R = 3.48 . Take the positive direction for current flow in each branch to be upwards.
EMF = V
left branch= A
right branch= A

2. Relevant equations

Kirchhoff's circuit laws

3. The attempt at a solution

I added current lines to the diagram. Note that a coordinate system is imposed and all positive charges point up ( I guess this makes grading easier). I sketched the lines of current as best I could.

Here are my equations:

Left loop:

1.00v-3.48I1-E+(.05*2)

Outside loop:

1.00v-3.48I1-1.00I3+1.20V+4.00I3=0 (edit: caught a mistake here, last term should have been positive)

Apply junction rule to top center junction:
I1+.05=I3

Combine terms:
1.00v-3.48I1-E+.1=0
2.20v-3.48I1+3.00I3=0

Substituting I1+.05 for I3:

2.20v-3.48I1+3.00I1+.15=0

Combining like terms:

2.35-.48I1=0

I1(the left loop)=4.90A which is wrong.

Any ideas where I messed up?

Last edited: Feb 20, 2008
2. Mar 20, 2010

### coolram80295

Where is the circuit diagram???????????????

3. Mar 20, 2010

### Bob Loblaw

Blast from the past! I have since moved past physics and on to medicine so things worked out well enough I suppose.