Solving a circuit using both the mesh and node analysis

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Homework Help Overview

The problem involves analyzing a circuit to find the currents i1, i2, and i3 using both mesh and node analysis methods. Participants are discussing their approaches and the equations derived from the circuit diagram.

Discussion Character

  • Mixed

Approaches and Questions Raised

  • The original poster attempts to solve for the currents using mesh analysis and then confirm the results with node analysis. They express confusion regarding the setup of equations for node 3, particularly about the potential difference Vx.
  • Some participants clarify the definition of Vx based on the circuit diagram, indicating that Vx = V1 - V3.
  • Others suggest that the original poster may have made an error in solving the simultaneous equations and request more detailed steps for critique.

Discussion Status

Participants are actively engaging with the original poster's attempts, providing clarifications and questioning the setup of equations. There is an acknowledgment of the need for further examination of the calculations involved in solving the equations.

Contextual Notes

The original poster is working under the constraints of homework rules, which may limit the amount of direct assistance they can receive. There is an ongoing exploration of assumptions related to the circuit's potentials and current values.

kstorm19
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Homework Statement


The problem asks to solve for i1, i2, and i3 using the mesh method in the following circuit:

bBvuLXM

I will also include the link, because I noticed I am having trouble attaching the image to the post: https://imgur.com/a/bBvuLXM
upload_2018-5-28_22-12-5.png

I would also like to confirm the answer by solving using the node analysis.
2egYIv0

2. Homework Equations

V=IR

The Attempt at a Solution


First of all, I solved for all three currents using the mesh analysis.
i1 = 5 A
For mesh 2, this is the equation I came up with:
12i2 + 11(i2-i3) + 13 (i2-i1) = 0

And so, using the Node 3:
i3 = 5+ 1/3 Vx
But Vx = 13i3
So i3 = 5 + 13/3 i3
i3= -1.5 A

Going back to equation for mesh 2 and solving for i2:
i2= -1.35 A

So I have:
i1 = 5 A
i2= -1.35 A
i3= -1.5 A

I wanted to confirm these results using the node analysis.

For node 1

(V1-V2)/12 + V1/11 + (V1-V3)/13 = 0

For node 2

(V2-V1)/12 + V2/13 = 5

For node 3

(V3-V1)/13 + 1/3 Vx + 5 = 0

So in this last equation I got a little confused, since when I was setting it up, V3 has the highest potential. If Vx = V1-V3 by looking at the arrow, should I write it that way in the equation, or should I put instead V3-V1?

I figured that maybe it should be written using V3-V1, so this is how I wrote the equation for node 3:

(V3-V1)/13 + 1/3 (V3-V1) + 5 = 0

Solving these 3 equations, I got:

V1 = 6.036 V
V2 = -0.061 V
V3 = -18.23 V

Now, replacing for Vx, which should be -19.5 V since Vx = 13i3 and i3=-1.5 A, I don't get that answer.

I also tried (V3-V1)/13 + 1/3 (V1-V3) + 5 = 0 for the third node equation in case I was wrong and I got:

V1 = -6.64 V
V2 = -3.21 V
V3 = 12.58 V

Now, subtracting V1-V3 gets me -19.22 V (almost -19.5 V from the mesh analysis).
But looking to confirm that i2=-1.35 A, (V2-V1)/12 doesn´t get me anywhere near that value. Where did I go wrong?

Thank you so much guys for your time and help.
 

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kstorm19 said:
So in this last equation I got a little confused, since when I was setting it up, V3 has the highest potential. If Vx = V1-V3 by looking at the arrow, should I write it that way in the equation, or should I put instead V3-V1?
From the circuit diagram, ##V_x = V1 - V3##
 
gneill said:
From the circuit diagram, ##V_x = V1 - V3##

Thank you for clearing my doubt in this part of the problem! I would also like to thank the mod that included my image in the post.

So now I know the second set of equations is the correct one. It is consistent with V1-V3 being -19.5V as Vx=13i3 is -19.5 V as well. What I'm not so sure about is the second current (i2), it definitely doesn´t get me the value that I got using the mesh analysis. What am I missing here? Thank you so much guys for your help.
 
I think that the problem must lie somewhere in your work in solving the simultaneous equations. You'll have to show the step-by-step details for us to critique it.
 

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