Finding 2 Unknown Currents and Voltage with Resistance

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Discussion Overview

The discussion revolves around solving a circuit problem involving two unknown currents (I1 and I2) and voltage (V) across a 6Ω resistor, given certain known values and equations. Participants explore various approaches to apply Kirchhoff's Current Law (KCL) and equivalent resistance concepts to find the unknowns.

Discussion Character

  • Homework-related
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses uncertainty about how to start solving the problem, mentioning an attempt to use KCL but feeling overwhelmed by the unknowns.
  • Another participant points out that the initial KCL equation presented is incomplete and suggests considering the net current source when dealing with two current sources in parallel.
  • A participant proposes finding the equivalent resistance of the two resistors and calculates a net current source of 10A, questioning if this approach is correct.
  • There is a discussion about the direction of current through the resistors, with one participant stating that the two current sources drive their currents in opposite directions, which affects how they combine.
  • Another participant suggests that combining the resistors simplifies the problem and attempts to derive voltage using the relationship V=IR, but expresses doubt about their assumptions and calculations.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the correct approach to the problem. There are competing views on how to handle the current sources and the application of KCL, leading to uncertainty about the next steps in the solution process.

Contextual Notes

Participants express uncertainty about the setup of equations and the assumptions regarding current directions. There are unresolved mathematical steps and dependencies on how the current sources interact within the circuit.

RainbowTuba
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Homework Statement


Find V, I1, I2 and the power of the 6Ω resistor:
BbnJDSD.jpg

Known:
R1=6Ω
R2=3Ω
Iknown1=8
Iknown2=2
RTotal=2Ω

Homework Equations


P=V2/R
P=IV
V=IR

The Attempt at a Solution


To be honest, I've been staring at the problem for hours not knowing where to begin. I thought I'd start with a KCL equation to find I1 and I2, but I'm left with too many unknowns to continue on.
I tried using a point above the 6Ω resistor as a node to find the KCL: Using V1 as my voltage at the node.
-8 -I1+I2=0
= (V1-V)/3 = 8+(V1-V)/6
= V1=V+48
But I don't believe I'm setting up the equation right in the first place.
 
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RainbowTuba said:

Homework Statement


Find V, I1, I2 and the power of the 6Ω resistor:
BbnJDSD.jpg

Known:
R1=6Ω
R2=3Ω
Iknown1=8
Iknown2=2
RTotal=2Ω

Homework Equations


P=V2/R
P=IV
V=IR

The Attempt at a Solution


To be honest, I've been staring at the problem for hours not knowing where to begin. I thought I'd start with a KCL equation to find I1 and I2, but I'm left with too many unknowns to continue on.
I tried using a point above the 6Ω resistor as a node to find the KCL: Using V1 as my voltage at the node.
-8 -I1+I2=0
= (V1-V)/3 = 8+(V1-V)/6
= V1=V+48
But I don't believe I'm setting up the equation right in the first place.

Welcome to the PF.

This equation of yours: -8 -I1+I2=0 is incomplete.

Instead, what can you say when you have 2 current sources in parallel? What is the net current source that drives the parallel resistor combination?
 
berkeman said:
Welcome to the PF.

This equation of yours: -8 -I1+I2=0 is incomplete.

Instead, what can you say when you have 2 current sources in parallel? What is the net current source that drives the parallel resistor combination?

So I can find an equivalent resistance of the two, which would equal 2, and the net current source would be 10A.

I figured since the unknown current is a factor, simplifying the circuit would combine the two, is this incorrect?

So would I use
-2-8 -I1+I2=0
instead?
 
RainbowTuba said:
So I can find an equivalent resistance of the two, which would equal 2, and the net current source would be 10A.

I figured since the unknown current is a factor, simplifying the circuit would combine the two, is this incorrect?

So would I use
-2-8 -I1+I2=0
instead?

The two current sources drive their current through the resistors in opposite directions, so they don't add.

And once you have the correct net current driving through the resistors, combine the two resistors into the equivalent resistance to find Vout. Then use Vout and the individual resistance values to...
 
berkeman said:
The two current sources drive their current through the resistors in opposite directions, so they don't add.

And once you have the correct net current driving through the resistors, combine the two resistors into the equivalent resistance to find Vout. Then use Vout and the individual resistance values to...

Yes they do, so instead of -10 it would be -6. Combining the resistance and capacitance would lessen the unknowns by one, so R=2 and I is our unknown

So:
-6 = I
which would make V=IR=(-6)2=-12, my assumed direction of I was wrong, so V=12, am I on the right track?

I feel like I did something wrong...
 

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