Solve Resistor Problem: Imagine Voltage Source from a to b

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Discussion Overview

The discussion revolves around the proper approach to a resistor problem involving an imagined voltage source between points a and b. Participants explore the implications of this assumption on the configuration of resistors and the calculation of equivalent resistance, focusing on the relationships between different resistors in the circuit.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant questions the validity of imagining a voltage source between a and b, suggesting that it may not be appropriate for determining the configuration of the resistors.
  • Another participant clarifies that the focus should be on finding the equivalent resistance between points c and d, indicating that the 5 ohm and 6 ohm resistors are not in parallel as initially suggested.
  • A different viewpoint proposes using a Thevenin equivalent circuit to analyze the resistors, providing formulas for calculating the Thevenin voltage and resistance.
  • One participant raises a concern about the lack of information regarding whether points a and b are connected to anything, which could affect the solution approach.
  • Another participant suggests that if a and b are open circuits, the 5 ohm resistor can be ignored, indicating that the proposed approach may be overly complex without a voltage source present.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of imagining a voltage source between a and b, with some arguing it is not valid while others provide alternative methods for analysis. The discussion remains unresolved regarding the correct approach to the problem.

Contextual Notes

There are limitations regarding the assumptions about the connections at points a and b, which are not clearly defined in the problem statement. This ambiguity affects the applicability of various methods discussed.

BigFlorida
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For this problem I am just wondering if it is proper to "imagine" there is a voltage source from a to b so that one may say the 5 ohm resistor right after a is in parallel with the 6 ohm resistor connecting the two wires. If not, how would I go about solving this?

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Thank you in advance.
 
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Why a and b? You are looking for the equivalent resistance between c and d. There you can add a voltage source.

There is no 5 ohm resistor in parallel to a 6 ohm resistor indepenent of the points you consider.
 
BigFlorida said:
one may say the 5 ohm resistor right after a is in parallel with the 6 ohm resistor connecting the two wires.
You could substitute the two resistors with a Thevenin-equivalent with a voltage source, VT and a resistor, RT:

VT = Vab * 6Ω / ( 5Ω + 6Ω )

RT = 5Ω || 6Ω

. . . and so on.
BigFlorida said:
If not, how would I go about solving this?
Use Kirchhoffs laws ( KVL and KCL ), set Vab = 100V, then calculate Vcd when cd is unloaded.
Then calculate ( KVL and KCL ) Icd when cd is short circuited.
Req = Vcd / Icd
 
Are a and b connected to anything? The problem statement does not mention this.
If they are not connected, the problem can be solved with parallel and series resistances only.
If they are connected, the posted problem statement is incomplete.
 
bigFlorida... You might be over thinking the problem.

a and b are open circuit so the 5R can be ignored.

The approach you suggested could be applicable _if_ there was a voltage source connected but you can't just add one.
 

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