Circuit analysis is this correct?

[Questions999]

Homework Statement

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

Homework Equations

Nod potential method,KVL.

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 don't know how to find ia..my tutor says that there's a missing equation and he wrote V(1/6+1/1+1/2)-4(1/1+1/6)=3V1 but I don't get this :/

 

[gneill]

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.

 

[Questions999]

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