Circuit analysis is this correct?

1. May 26, 2013

Questions999

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

We have the problem in the figure.I have to find the potential across 12 Ohm using nod potential method.

2. Relevant equations

Nod potential method,KVL.

3. The attempt at a solution

I write the potential for the nod a and I have (Va-Vb)/4 + Va/2= 2A (1)
I write the potential for the nod b (Vb - Va)/4 +Vb + Vb/2=3 V1 (2)
V1 = Va so for the (1) equation I multiply both sides with 4 and I have 3Va- Vb=8
For the (2),after I replace V1=Va and I have 13Va+ 7 Vb=0 . I put the (1) in the (2) and I have Va=7 and Vb=13 so ib=(7-13)/4 =-3/2...I dont know how to find ia..my tutor says that theres a missing equation and he wrote V(1/6+1/1+1/2)-4(1/1+1/6)=3V1 but I dont get this :/

2. May 26, 2013

Staff: Mentor

I don't see a 12 Ω resistor in your circuit or in your analysis attempt.

In your equation for the second node, for the current through the 1 Ω resistor you've failed to take into account that the resistor terminates in a potential of 4V, not at ground.

3. May 26, 2013

Questions999

oh sorry,I have to find the potential across the resistor 4 Ohm...