When Is Node Voltage Not Equal to Voltage Source?

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Discussion Overview

The discussion centers around the conditions under which the voltage at a node connected to a voltage source may not equal the voltage of that source. Participants explore the application of voltage division in circuit analysis, particularly in scenarios involving series and parallel resistances.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions when the voltage at a node connected to a voltage source differs from the source voltage, expressing confusion about applying voltage division in such cases.
  • Another participant suggests that voltage division can typically be applied when resistors are in series across a voltage source, assuming no other power sources are present.
  • A participant seeks a general rule for applying voltage division to portions of a circuit, noting that while it is primarily used for series resistances, there may be ways to account for parallel resistances as well.
  • One participant inquires whether voltage division is applicable in a closed loop even when a branch leads to an interface or output, referencing a specific circuit example to illustrate their point.
  • A later reply provides a method for calculating current and output voltage in a circuit, using voltage division and substituting values to derive an expression for output voltage.

Areas of Agreement / Disagreement

Participants express differing views on the applicability of voltage division in various circuit configurations, indicating that multiple competing perspectives remain without a clear consensus on the general rule for its application.

Contextual Notes

Participants note limitations in their understanding of voltage division, particularly regarding its application in circuits with complex arrangements, and the need for further analysis in such cases.

Who May Find This Useful

This discussion may be of interest to students and practitioners in electrical engineering or physics, particularly those dealing with circuit analysis and voltage division concepts.

skyfire101
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when does the voltage of a node with a branch attached to a voltage source not equal the voltage of the voltage source?
This question has been driving me crazy because i am unsure when i am able to apply voltage division to portions of a circuit i try to analyze.
I know the potiential difference across a voltage source always needs to be equal to the value of the voltage source but, if the branch coming out of a voltage source is not at the same potiental as the voltage source how can i apply voltage division?
Any help is much appreciated, thank you
 
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Can you draw a diagram?

You can usually apply voltage division if you have resistors in series across a voltage source, provided there is no other power source in the circuit.

However, more complex arrangements mean you have to use analysis to get the voltages.
 
I'm really just looking for a way to apply to apply the rule in general, or to portions of a circuit. I know that voltage division is used mostly for resistances in series, however there are ways to compensate for parallel resistances to. So i was wondering to what scope voltage division applies. My txtbook has examples where it applies it to portions of a circuit, but doesn't explain why it works in said examples.

Is it accurate so say that voltage division still applies to a closed loop even when one branch leads to some interface or output?
In my attachment is the circuit of suspect, it asks to find Vo in terms of input Vs, I can only match the equation they get by using voltage division on the loop containg Vs
i.e
Ix*Rp = Vs*Rp/(Rs+Rp)
(Rp on left gets canceled)

and then sub Ix into another equation that uses volt division on the loop with a dependent source.
i.e
Vo = (-rIx)*RL/(RC + RL)
(sub previous eqn into Ix)
*above Vo should be "+" and below Vo "-" sign
 

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You can get the current in the left circuit with Vs / (Rs + Rp). call this current I1

The current source gives this current times r

So this current flows in Rc and RL.

The voltage drop across RL is then I1 * r * RL

Substituting for I1
The output voltage = {Vs / (Rs + Rp)} * r * RL
 

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