Homework Help: Finding the Potential at a specific point in this Circuit

1. Jul 25, 2014

tmint

1. The problem statement, all variables and given/known data
What is the Electric Potential at Point A?
Battery 1: 6.76 V
Battery 2: 11.8 V
Resistance 1: 100Ω
Resistance 2: 217Ω
Resistance 3: 312Ω

2. Relevant equations
Kirchhoff's Rules
V=IR

3. The attempt at a solution

I first set up my Currents so that Current 1(left)+ Current 2(down middle)= Current 3(right)

Let c be left of point a, b the point bottom of point a, d left of b, e right of point a and f right of b.

cabdc: -217(Current 1)+100(Current 2)=-6.76
=-217(Current 1)+100(Current 2)

aefba: -312(Current 3)-11.8-100(Current 2)=0
=-312(Current 3)-100(Current 2)=11.8

Let Current 2= Current 3-1

So..

-217(Current 1)+100(Current 3-1)=-6.76

-312(Current 3)-100(Current 3-1)=11.8

And I get

312(Current 3)-217(Current 1)+200(Current 3-Current 1)=-18.56

I'm stuck at this step, could use some help.

Thanks.

2. Jul 25, 2014

Staff: Mentor

It is difficult to spot errors (and easy to make them) when working without a diagram. But the two statements below seem to lack compatibility. Check the signs/directions you are using.

cabdc: -217(Current 1)+100(Current 2)=-6.76
Current 2= Current 3-1

Last edited: Jul 25, 2014