Solve Mesh Analysis Problem: Find Current Through 4 Ohm Resistor

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Discussion Overview

The discussion revolves around solving a mesh analysis problem to find the current through a 4 Ohm resistor in a circuit. Participants explore the formulation of mesh equations, the use of simultaneous equations, and methods for solving systems of equations, including Gaussian elimination and Cramer's rule.

Discussion Character

  • Homework-related
  • Mathematical reasoning
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents their mesh equations and seeks confirmation on their correctness.
  • Another participant suggests that the original equations are slightly incorrect and provides their own version, noting that the current through the 4 Ohm resistor is I1 - I2.
  • Further clarification is provided on the correct formulation of the equations, with some participants reiterating the same equations.
  • A participant inquires about how to find individual currents from a different set of mesh equations and mentions Gaussian elimination as a potential method.
  • Another participant outlines the use of Cramer's rule to find the currents based on determinants of matrices derived from the equations.
  • Discussion includes a brief mention of the determinant calculation method and the importance of sign conventions in matrix determinants.

Areas of Agreement / Disagreement

There is no consensus on the correctness of the initial mesh equations, as multiple participants provide different versions. The discussion includes various methods for solving the equations, but no final agreement on a single approach is reached.

Contextual Notes

Participants express uncertainty regarding the accuracy of the mesh equations and the methods for solving them. There are also limitations in the clarity of the uploaded circuit image, which affects the discussion.

Who May Find This Useful

This discussion may be useful for students learning about mesh analysis, circuit analysis techniques, and methods for solving systems of linear equations in electrical engineering contexts.

Kobayashi
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Homework Statement


Use mesh analysis to find the current through the 4 Ohm resistor.


Homework Equations





The Attempt at a Solution


From this circuit I managed to work out the three mesh equations using mesh analysis.

Mesh 1 = 7I1 + 4I2 = 67
Mesh 2 = -4I1 + 15I2 - 6I3 = 152
Mesh 3 = -6I2 + 13I3 = 74

Are these mesh equations correct.
From this point in the question how do I calculate the current through the 4 ohm resistor. I know you use simultaneous equations but I can't get the correct answer. Please help.
 

Attachments

  • Mesh Analysis.jpg
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I am unable to view the .jpg. Does one of the moderators know why that is? I'm using the Firefox browser.
 
I also use firefox and it works for me. Have you tried internet explorer?
 
IE doesn't work either. I see the little symbol for a broken link. Maybe the link points to something which is on your own computer, but not accessible through the internet. Can you post the URL to the picture as simple text?
 
I tried uploading it again.
 

Attachments

  • Mesh Analysis.jpg
    Mesh Analysis.jpg
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still not working for me. If you right click on it and then click properties, what is the URL?
 
Well, now the link is working! I wonder what changed?

Your equations are a little bit off. I get:

7 I1 - 4 I2 + 0 I3 = 67

-4 I1 + 15 I2 - 6 I3 = -152

0 I1 - 6 I2 + 13 I3 = 74

Don't forget that the current in R4 is not just one of these currents; it's I1 - I2.

Do these equations give you the correct result? Do you see where you went wrong?
 
the correct equation is :
7 I1 - 4 I2 = 67

-4 I1 + 15 I2 - 6 I3 = -152

- 6 I2 + 13 I3 = 74
 
  • #10
the correct equation

the correct equation is :
7 I1 - 4 I2 = 67

-4 I1 + 15 I2 - 6 I3 = -152

- 6 I2 + 13 I3 = 74
Use matrix to find the value of I1,I2 and I3 then u find he value of current in 4 ohm is
4I1-4I2=IR4
 
Last edited:
  • #11
Thanks.
I now have a question about analysis of a circuit containing three meshes.
When you get an equation e.g:

-11.3I1 + 9.1I2 +0I3 = 18
9.1I1 -23.4I2 + 6.8I3 = -18
0I1 + 6.8I2 -10.1I3 = -3

How do you find the individual currents in this case. I read you can use Gaussian Elimination. How does that work in this case. Thanks.
 
  • #12
Kobayashi said:
Thanks.
I now have a question about analysis of a circuit containing three meshes.
When you get an equation e.g:

-11.3I1 + 9.1I2 +0I3 = 18
9.1I1 -23.4I2 + 6.8I3 = -18
0I1 + 6.8I2 -10.1I3 = -3

How do you find the individual currents in this case. I read you can use Gaussian Elimination. How does that work in this case. Thanks.

The easier u use crimer rule :



I1= (detB/detA)

I2=(detC/detA)

I3=(detD/detA)

where

A=

-11.3000 9.1000 0
9.1000 -23.4000 6.8000
0 6.8000 -10.1000


B=

-11.3000 9.1000 18.0000
9.1000 -23.4000 -18.0000
0 6.8000 -10.1000


C=


-11.3000 18.0000 0
9.1000 -18.0000 6.8000
0 -3.0000 -10.1000



D=


18.0000 9.1000 0
-18.0000 -23.4000 6.8000
-3.0000 6.8000 -10.1000




To find the det ...for example let take matrix X=


a b c
d e f
g h i


be careful about the sign which it equivalent to

+ - +
- + -
+ - +

det(X)=a (ei-hf)-b(di-gf)+c(dh-ge)


and so on...
 
  • #13
Thanks, that helps me a lot. I've learned matrices before but I've completely forgotten. Thanks for reminding me.
 
  • #14
This forum isn't really the place to explain Gaussian elimination.

Go read: http://en.wikipedia.org/wiki/Gaussian_elimination.

Another alternative is to get a calculator that can do matrix arithmetic, or a program for your PC, such as Scilab.
 

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