KVL/KCL with two sources - can a loop have both sources?

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Homework Help Overview

The discussion revolves around a circuit analysis problem involving Kirchhoff's Voltage Law (KVL) and Kirchhoff's Current Law (KCL) with two voltage sources. The original poster (OP) seeks clarification on the validity of including multiple voltage sources in their equations and how to approach the problem of finding currents and power in the circuit.

Discussion Character

  • Exploratory, Assumption checking, Problem interpretation

Approaches and Questions Raised

  • The OP questions whether it is valid to include two voltage sources in their KVL equations and seeks guidance on any rules regarding this. Other participants discuss the implications of having multiple sources and the correct setup of equations, noting potential errors in the OP's approach.

Discussion Status

Participants are actively engaging with the OP's questions, providing insights into the validity of including multiple sources in KVL. Some have pointed out potential errors in the OP's equations and suggested corrections, indicating a productive exchange of ideas without reaching a consensus on the final solution.

Contextual Notes

The OP mentions constraints related to homework guidelines directing them to post in this section, which may influence the nature of the discussion. Additionally, there are indications of confusion due to fatigue, which may affect the clarity of the OP's initial posts.

chopnhack
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Homework Statement


In the circuit shown, find (a) the current in each resistors (b)The power dissipated in each resistor.

Homework Equations


V=IR, P=VI, KVL and KCL

The Attempt at a Solution


See attached.

I was going to post this in the main section as its really a question about whether you can have two voltage sources in your equation, but I read the sticky on the main page for general physics and it directed all coursework type questions here.

In the drawing I have a section underlined. When I set up my equations, I got two voltages in the equation. I wanted to know if that is valid? If I should come across another equation like this, is there a rule for knowing not to do this? The solution to this problem is not the same as what I derived. Please give me some direction with this, thanks!
 
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Sure, a given loop can contain zero or more sources. For KVL their potential changes sum just as you've done.
 
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chopnhack said:
In the drawing I have a section underlined. When I set up my equations, I got two voltages in the equation. I wanted to know if that is valid? If I should come across another equation like this, is there a rule for knowing not to do this? The solution to this problem is not the same as what I derived. Please give me some direction with this, thanks!
Your second equation is incorrect.
There should be i2 instead of i1.
 
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gneill said:
Sure, a given loop can contain zero or more sources. For KVL their potential changes sum just as you've done.
Thanks mate! BTW - if you haven't seen the finale... jumping the shark abit... Still a fan though :-)

cnh1995 said:
Your second equation is incorrect.
There should be i2 instead of i1.
Hi CNH, I think I see the error now. The 5I1 should really be just I1 times the 1 ohm resistor. That makes it all work.
Thanks gents!
 
cnh1995 said:
Does it?

I1 flows through the 3 ohm resistance too. Plus, I2 also flows through the 3 ohm resistance. You should have all the three currents in that equation.
OP has 3 individual currents, each one for each branch of the circuit. He then uses a junction equation to relate them.
 
Last edited:
It was almost 12 am when I posted it and I was kinda sleepy:oops:. I guess I have to sleep now before I post anything stupider.
SammyS said:
OP has 3 individual currents, each one for each branch of the circuit. He then uses a junction equation to relate them.
Yes. I wasn't able to delete that because of network problems (I am traveling in a hilly area).
Fixed it now.
 
Last edited:

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