Understanding KVL and Voltage Differences

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Discussion Overview

The discussion revolves around the application of Kirchhoff's Voltage Law (KVL) in a homework problem involving voltage differences in a circuit. Participants explore the calculations related to voltage around a loop and the discrepancies between their results and the professor's posted answer.

Discussion Character

  • Homework-related, Technical explanation, Debate/contested

Main Points Raised

  • One participant outlines their approach using KVL, stating that the sum of voltage differences in a loop should equal zero, leading to a calculation of Vx as -3.
  • Another participant suggests that using node analysis could yield a quicker solution, providing an equation that also results in Vx = -3.
  • A third participant asserts that the original poster's solution is correct and implies that the professor made a mistake.
  • A later reply indicates that the professor confirmed it was a typo, stating the correct answer is -3.

Areas of Agreement / Disagreement

There is disagreement regarding the professor's posted answer, with some participants supporting the original poster's calculation of Vx = -3, while one participant initially suggests the possibility of a typo in the professor's answer. The discussion reflects uncertainty about the correctness of the professor's answer.

Contextual Notes

Participants rely on different methods (KVL vs. node analysis) to arrive at their conclusions, and there is an acknowledgment of potential errors in the professor's posted answer. The discussion does not resolve the validity of the methods used, nor does it clarify the assumptions behind the calculations.

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Homework Statement


eceKVL.jpg

Homework Equations


KVL, the sum of all voltages around a loop equal 0

The Attempt at a Solution


eceKVLsol.jpg


Vx is just the difference of the bottom node to the right node. With KVL I just add up the the voltage differences in a loop and equal to zero right? -15+12+6+Vx=0 Vx = -3 ... However my professor posted the answer and Vx = -9 ... why is that? what am I doing wrong?
 
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Not sure I never use KCL/KVL anymore lol.

If you know how to use node analysis you can get the answer more quickly and easily.

Establish a node as ground and the voltage at the node you want to solve you just sum the currents into that node to zero.

Establishing the right node as ground:

node analysis equation:

(3-Vx)/3 - 2 = 0

Which solves for Vx = -3

I actually ended up with the same answer as you, perhaps you should ask your professor if it's a typo?

I could've solved it incorrectly as well though.
 
Your solution is correct. Your professor made a mistake.
 
thanks for the help! i just got an email and it was a typo and the answer is -3
 

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