Voltage Drop and Equivalent Resistance in a Circuit

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Discussion Overview

The discussion revolves around understanding the voltage across terminals in a circuit, specifically in relation to the voltage drop across certain resistors. Participants explore concepts related to current division, Thevenin and Norton equivalent circuits, and the implications of open circuit conditions.

Discussion Character

  • Homework-related
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant questions why the voltage across terminals a and b is the same as the voltage drop across a branch with specific resistors, indicating a need for clarification on this relationship.
  • Another participant explains that voltage is measured between two points and that current flows through components, suggesting a potential terminology issue.
  • A participant realizes that the terminals being open was a key factor in understanding the problem, leading to a consideration of equivalent circuits.
  • Further clarification is provided that the voltage across the terminals will remain consistent with the voltage across a connected resistor, regardless of additional connections or components.
  • A participant acknowledges their confusion stemmed from a lack of experience with circuits, indicating a learning process rather than a definitive understanding.

Areas of Agreement / Disagreement

Participants generally agree on the principles of voltage measurement and the implications of open circuits, but there is no consensus on the initial confusion regarding the relationship between terminal voltage and voltage drop across resistors.

Contextual Notes

Participants express uncertainty about terminology and foundational concepts in circuit analysis, which may affect their understanding of the problem.

Gecata
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Homework Statement


Task: Find the voltage across the terminals a and b in the circuit (Done).
My question: Why does the solution work?

Homework Equations


Current division
ix = Isource * Gbranch/Gequivalent

The Attempt at a Solution


The voltage across (or is it between ?) the terminals is the same (why ?) as the voltage drop at the branch with the 2, 12 and 10 Ohm resistors, which is 45 Volts. This was found by first finding the current flowing through the branch with the current division principle, i = 3.75 A.

As I stated above, why is the voltage across the terminals the same as the voltage drop at the branch with the 2, 12 and 10 Ohm resisotrs?

The circuit is attached below.

circuit.jpg
 
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Gecata said:

Homework Statement


Task: Find the voltage across the terminals a and b in the circuit (Done).
My question: Why does the solution work?

Homework Equations


Current division
ix = Isource * Gbranch/Gequivalent

The Attempt at a Solution


The voltage across (or is it between ?) the terminals is the same (why ?) as the voltage drop at the branch with the 2, 12 and 10 Ohm resistors, which is 45 Volts. This was found by first finding the current flowing through the branch with the current division principle, i = 3.75 A.

As I stated above, why is the voltage across the terminals the same as the voltage drop at the branch with the 2, 12 and 10 Ohm resisotrs?

The circuit is attached below.

View attachment 78771
Hi Gecata, Welcome to Physics Forums.

Yes, voltage (or potential difference) is measured between two points or across a component. Current goes though a wire or component.

Perhaps there's a terminology issue, but I 'm not entirely clear on your problem. Can you show your work?
 
Actually I see the answer to my question now (not really a question apparently).
The terminals A and B are open, and I needed to determine the resistance between them, in order to model a Thevenin and Norton equivalent circuits.

The confusing momenta was not really paying attention to terminals A and B being open.

I saw my mistake after reading your answer, so in a way you answered my question. Thank you.
 
As I stated above, why is the voltage across the terminals the same as the voltage drop at the branch with the 2, 12 and 10 Ohm resisotrs?

It's not just because a and b are open circuit...

Points a and b are connected to the 12 ohm resistor by ideal wire so the voltage Vab will always be the same as the voltage across the 12 ohm resistor... EVEN if points a and b were connected together with a wire, another resistor or something more complicated like a battery. For example if you connected a and b to a 10V battery the voltage drop across the 12 Ohm resistor would be 10V.
 
Yes, I understand that. My confusion was caused by something else entirely, namely not enough experience with circuits. Thanks again for the explanation.
 

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