# Is this electrical circuit solvable?

I am trying to solve a circuit with two current sources.

I1, I2, V1, V2 are known. R1, R2, R3 are unknown.

I've tried node analysis, but I can only come up with two equations

$\dfrac{V_2}{R_1} + \dfrac{V_2-V_1}{R_2} = I_1 \tag{1}$

$\dfrac{V_1-V_2}{R_2} + \dfrac{V_1}{R_3} = I_2 \tag{2}$

so I have two equations and three unknowns.. How can I get the third equations?

• Try researching "superposition" in relation to electrical circuits. Jun 6 '13 at 20:15
• Apart from V1 and V2, there is a third node of which you didn't write down the equation yet. Take a good look at the circuit. Jun 6 '13 at 20:19
• jippie - Yes, the reference node at the bottom. But that doesn't really count, right? Jun 6 '13 at 20:25
• It matters. It will give you your third equation to solve for your 3 unknowns. Every node matters, just like every mesh matters if you are doing a complete analysis. Jun 6 '13 at 20:33
• Hm.. you guys are tantalizing me :) this is actually a thermal circuit problem, I am trying to calculate a very simple thermal model for a motor. So say reference node is V3. Then I have: (V1-V3)/R3 + (V3-V2)/R1=I1+I2 And since V3=0, then I have the 3d equation? Jun 6 '13 at 20:40

$\dfrac{V_2}{R_1} + \dfrac{V_1}{R_3} = I_1 + I_2$