Different voltages on the same node?

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Discussion Overview

The discussion revolves around the analysis of voltages at a specific node in an electrical circuit involving both independent and dependent voltage sources. Participants explore the implications of Kirchhoff's Voltage Law (KVL) and the concept of node voltage in the context of circuit analysis.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant asserts that node A has a voltage of 10V due to its connection to an independent voltage source, while also questioning how this can coexist with a dependent voltage source indicating 2V at the same node.
  • Another participant claims that the voltage at node A is definitively 10V, which determines the current through a resistor and consequently the voltage across the dependent source.
  • A different participant emphasizes that voltage is a potential difference between two nodes, suggesting that the concept of "node voltage" requires a reference point, typically ground.
  • Another participant clarifies that the 10V at node A is relative to a specific reference point, while the 2V across the dependent source is relative to another point in the circuit, indicating that these values need not be inconsistent.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation of voltages at node A, with some asserting a definitive voltage and others emphasizing the need for reference points in voltage measurements. The discussion remains unresolved regarding the compatibility of the voltages indicated by the independent and dependent sources.

Contextual Notes

There is an underlying assumption about the reference points for voltage measurements that is not explicitly stated, which may lead to confusion in the analysis. The discussion also highlights the importance of applying KVL correctly in different loops of the circuit.

yosimba2000
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In this picture: http://imgur.com/lfNiDjL

I see that at node A, the voltage is 10V since it is connected to the independent voltage source. But node A is also connected to the dependent voltage source 10Io.

If I do KVL on the left loop, Io comes out to be 0.2A. Plugging this into the dependent source, the dependent source is at 2V. How is this possible?

The dependent source says Node A is at 10V. But the dependent source says Node A is at 2V. Since both sourcers are connected at the same point, they should be at the same voltages, right?

Which voltage is correct? How am I analyzing this incorrectly?
 
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10V at node A, period. That fixes the current through R1, which determines the voltage across the dependent source, which is referenced to node A. The dependent source is 10V on the left side and 12V on the right since there is 2V across it.
 
yosimba2000 said:
In this picture: http://imgur.com/lfNiDjL

I see that at node A, the voltage is 10V

A single node cannot have a "voltage".
A voltage always is the potential DIFFERENCE between two nodes.
Only in case one node is grounded we speak about a "node voltage" - without mentioning that this automatically means: Referenced to the grounded node.
 
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yosimba2000 said:
I see that at node A, the voltage is 10V...

That is 10V wrt the bottom end of R1.

If I do KVL on the left loop, Io comes out to be 0.2A. Plugging this into the dependent source, the dependent source is at 2V.

That is 2V wrt the node between the dependent source and R2.

So they need not be inconsistent.

Mark these voltages on the drawing and apply KVL to the right hand loop.
 

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