Why Do My Calculations with Kirchoff's Laws Seem Incorrect?

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Homework Help Overview

The discussion revolves around a circuit problem involving Kirchhoff's Laws, specifically analyzing a circuit with a 24 V battery and two parallel resistors of 5 Ω and 7 Ω. The original poster is attempting to calculate the currents in the circuit but is encountering discrepancies between their Kirchhoff's Law calculations and results obtained using Ohm's Law.

Discussion Character

  • Exploratory, Assumption checking

Approaches and Questions Raised

  • The original poster sets up equations based on Kirchhoff's Laws but questions the validity of their results when compared to Ohm's Law. Some participants provide feedback on the calculations, suggesting that the original poster's approach may be correct.

Discussion Status

The discussion is ongoing, with some participants affirming the correctness of the original poster's calculations. There is an exchange of insights, but no explicit consensus has been reached regarding the discrepancies noted by the original poster.

Contextual Notes

The original poster expresses uncertainty about their understanding of the concepts involved, indicating a potential gap in their grasp of the relationship between Kirchhoff's Laws and Ohm's Law.

ahben86
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I was hoping someone could help out, I am working out a problem with Kirchoff's Laws and cannot seem to get the math to work out properly, at least I think the math is not working properly.
I was hoping to run it by someone here.

Homework Statement



The circuit is as follows:
A battery of 24 V on one end connected to two parallel resistors with values of 5 Ω and 7 Ω.
Mesh one will be the loop between the battery and the 5 Ω resistor, which has a current of I1.
Mesh two will be the loop between the 5 Ω resistor and the 7 Ω resistor, which has current of I2.

Homework Equations


The equations I set up are as follows:
0 = -24 + 5*(I1 - I2)
0 = 7*I2 + 5*(I2 - I1)




The Attempt at a Solution


After calculating the values I obtained these numbers:
I1 = 8.229 A
I2 = 3.429 A

I tried verifying these answers by using V = I*R
Finding Req to be 2.917 Ω.
Therefore I = V/R and I = 8.228 A and since the current from I1 is the same value it seems that the values obtained from Kirchoff's Laws do not match the Ohm's Law current.

I am uncertain if I am not realizing a concept but this does not make sense to me.

Any help is appreciated.
Thank you,
A.B.
 
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I think your work is all correct. V =IR finds the current through the resistors as 4.8 and 3.42 representing I1 - I2 and I2, so I2 = 3.42,
I1 - I2 = 4.8
I1 = I2 + 4.8
I1 = 3.42 + 4.8 = 8.23
 
thank you for your help Delphi, sorry I posted in the wrong area.
I think I understand now,

A. B.
 
Most welcome! This is the correct area for your question.
 

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