I am having trouble with circuit diagram involving multiple currents. We were taught the method of using junction/loop rules and systems of equations (or matrices) to find the current or voltage in a given spot. I think I understand the basic concept but am setting up my equations incorrectly.(adsbygoogle = window.adsbygoogle || []).push({});

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

Find the current in the 10.0[tex]\Omega[/tex] resistor in the drawing (V1 = 15.0 V and R1 = 27.0[tex]\Omega[/tex])

http://dl.dropbox.com/u/307214/20_82alt.gif [Broken]

2. Relevant equations

Kirchoff's rules...I don't think any actual equations?

3. The attempt at a solution

First I decided to pick a common start point for the problem as the lower right corner.

Then I labeled the currents in the circuit: I[tex]_{A}[/tex] as going to the right in the left branch, I[tex]_{B}[/tex] going to the right in the right branch, and I[tex]_{C}[/tex] going up across the middle.

I then setup 2 of my equations by going in a loop from my start point and adding or subtracting the voltages, so:

+15 + 10 - 27I[tex]_{A} [/tex] - 5I[tex]_{B}[/tex] =0 for going around the left branch and

15 + 10 - 10I[tex]_{C} [/tex] - 5I[tex]_{B}[/tex] =0 for going up the middle.

I then determined (perhaps incorrectly) that I[tex]_{A}[/tex]+I[tex]_{B}[/tex] =I[tex]_{C}[/tex]

From here I setup matrices on my calculator as such:

Matrix [A]

-27 -5 0

0 -5 -10

1 1 -1

and

Matrix

-25

-25

0

I then did [A][tex]^{-1}[/tex]*for the results:

.7042

1.1972

1.9014

None of these answers are correct :/

Any and all help is greatly appreciated!

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# Homework Help: Trouble with multiple-current circuit diagram problems.

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