Struggling with Nodal Analysis and Voltage Calculations

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Discussion Overview

The discussion revolves around the application of nodal analysis and voltage calculations in a circuit involving resistors and capacitors. Participants are exploring the discrepancies between their calculations and the expected results, particularly focusing on the voltages at various nodes in the circuit.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant reports obtaining a voltage of nearly 15 V for a node above a 5 kΩ resistor using nodal analysis, assuming capacitors are saturated and act as open circuits.
  • The same participant calculates voltages V1, V2, V3, and V4 using a loop analysis, finding a current of 0.5 mA through the resistors, which leads to different voltage values compared to nodal analysis.
  • Another participant suggests that V2 and V1 would equal V only if there were zero current through the 5 kΩ resistor.
  • One participant confirms the calculations for V1, V3, and V4 are correct and that the loop current is indeed 0.5 mA.
  • There is a question raised about the correctness of V2 and the differences revealed by nodal analysis.
  • Another participant points out an arithmetic error in calculating V, implying that this may be contributing to the discrepancies.

Areas of Agreement / Disagreement

Participants express differing views on the accuracy of the nodal analysis and the calculated voltages, with some agreeing on the correctness of certain calculations while others question the results and suggest potential errors. The discussion remains unresolved regarding the overall consistency of the methods used.

Contextual Notes

There are indications of potential arithmetic errors and assumptions about the behavior of capacitors in the circuit that may affect the calculations. The discussion does not resolve these issues.

gfd43tg
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I am having a little issue with this problem, because when I do nodal analysis, I get the voltage of the node above the 5 kΩ resistor to be nearly 15 V. I am assuming all of the capacitors are saturated, and therefore act as open circuits. That means no current goes through the 20k or 30k resistors, and therefore the voltage v2 and v1 should be the same as the voltage V, almost 15 V.

However, then I try a different approach and do a loop around the 5k, 15k, and 10k resistors, knowing all other wires lead to an open circuit. I get a current of 0.5 mA. Then to find v3, knowings its in parallel with the 15k resistor, I do the current times 15k to get the voltage, and similarly with the 10k and v4.

for v1 and v2, I do 15V - 5000(0.5x10^-3) = 12.5 V, which does not agree with my nodal analysis. What is going on here??
 

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V2 and V1 would equal V iff there were zero current through the 5k resistor.

Your calculations for V1, V3 and V4 are correct, the loop current is 0.5mA
 
Why is my nodal analysis revealing something different? Also, is my V2 correct?
 
Maylis said:
Why is my nodal analysis revealing something different? Also, is my V2 correct?
You have made an arithmetic blunder in calculating V.
 

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