Hello everyone, having troulbes applying Kirchoff's Rule~DC circuits

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Homework Help Overview

The discussion revolves around applying Kirchhoff's Rules in the context of DC circuits. The original poster presents a circuit diagram with specific resistances and battery voltages, seeking assistance with the calculations related to current and potential difference.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to set up equations based on Kirchhoff's Rules but encounters difficulties in substituting variables correctly. Some participants suggest substituting one variable into the equations to simplify the problem, while others point out potential errors in the equations derived.

Discussion Status

Participants are actively engaging in the problem-solving process, with some providing guidance on how to manipulate the equations. There is recognition of mistakes in the original equations, and suggestions are made to correct these errors. The discussion is ongoing, with no explicit consensus reached yet.

Contextual Notes

The original poster indicates that this is their first problem involving Kirchhoff's Rules, which may imply a learning curve regarding the application of these concepts. There are references to specific circuit configurations and equations that may require further clarification.

mr_coffee
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Hello everyone, this is my first problem dealing with Kirchoffs Rule and I thought I did it right...here is the circuit...
http://www.webassign.net/hrw/hrw7_27-40.gif
the info is the following:
In Figure 27-40, the resistances are R1 = 1 , R2 = 2.2 , and the ideal batteries have emfs E1 = 2.0 V, and E2 = 3 = 3 V.


Fig. 27-40

(a) What is the current through each battery? (Take upward to be positive.)
battery 1 A
battery 2 A
battery 3 A

(b) What is the potential difference Va - Vb?
V

I came out with the following 3 equations:
E1 + (-R1)(I_1) + R2*I_2 - E2 -R1*I_1;
-R2*I_2 + R1*I_3 - E3 + R1*I_3 + E2;
I_1 + I_2 + I_3 = 0;

When i solve for I_1 = -I_2 -I_3
Where do I plug I_1 into? i tried the first equation and i couldn't solve for any I, and i can't for the 2nd, because there is no I_1, did i do this right? thanks!
 
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Substitute for I_2 = -I_1 - I_3 into both the first two eqns, since it is common to both.
Then you will have two eqns in two unknowns.
 
Thanks! that worked out great, but I messed somewhere writing out the 2nd circuit on the right...This is the equation i got and the work:
http://img477.imageshack.us/img477/956/lastscan6lq.jpg
its wrong...
The first one, i did, on the left, was right though. Any help would be great.
 
Last edited by a moderator:
On your last line - in the attachment - the -R1.I2 should be +R1.I3.

It looks like this mistake was copied through from the line before it.
 

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