Definition of electrical branch

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Discussion Overview

The discussion centers around the definition of an electrical branch in circuit analysis, particularly in relation to generators and resistors in series. Participants explore the implications of these definitions on circuit analysis and the application of Kirchhoff's rules.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • Some participants propose that a branch is defined as a single length conductor with zero impedance connecting two nodes, leading to a single current flowing in that branch.
  • Others challenge the requirement of zero impedance for a branch, suggesting that anything connecting two nodes could be considered a branch.
  • A participant questions whether a generator fits the definition of a branch, seeking clarification on its classification.
  • There is a discussion about whether two resistors in series constitute one branch or two branches, with differing opinions on the necessity of nodes for defining branches.
  • Some participants assert that a resistor has a node at each end, while others argue that a node requires at least three branches meeting at that point.
  • One participant mentions the need for connection points to be named or identified, referring to them as nodes, while the connections are termed branches.
  • There is a reference to the use of incidence matrices or netlists in specifying electrical networks, indicating a potential divergence in terminology and understanding among participants.

Areas of Agreement / Disagreement

Participants express differing views on the definition of a branch, the role of impedance, and the classification of components like generators and resistors in series. The discussion remains unresolved with multiple competing perspectives present.

Contextual Notes

Participants reference different interpretations of nodes and branches, indicating potential limitations in definitions and assumptions that may vary between classical circuit analysis and other contexts.

nebbione
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Hi everyone! I wanted to know why in the circuit analysis a generator doesn't represent an electrical branch?
And the second question is if two resistors are in series on a wire, does it represents only a branch(the series of the resistance) or two branches ?
 
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A branch is a single length conductor with zero impedance connecting two nodes.
The potential is the same along the whole length of the branch and at both nodes.
There is therefore only one current flowing in any branch; this is called the branch current.

Does a generator conform to this definition?
 
Studiot said:
A branch is a single length conductor with zero impedance connecting two nodes.
Zero impedance? Where did you get this requirement from?
I did not find anywhere (yet) this definition. I thought that anything between two nodes is a branch (if there is no other node).

Just a couple of internet places where they don't assume this zero impedance for a branch:
http://en.wikipedia.org/wiki/Nodal_analysis
http://www.allaboutcircuits.com/vol_1/chpt_10/2.html

Regarding OP: Can you show details of the situation where the generator is not considered "a branch"?
 
Strictly, even a resistor has a node at each end.

You connect nodes by branches.

Mostly humans are intelligent enough to condense this to including the resistor in the 'branch', but computers are not.

Thus a generator is simply a 'component' with two nodes (terminals).
 
Studiot said:
Strictly, even a resistor has a node at each end.
Even when you have two series resistors in a "branch"?

I thought that to have a node you need to have at least three branches meeting at that point. Not every point or terminal is a node. In a simple series circuit with 10 resistors and one source, for example, there are no nodes.

PS. Maybe your terms are from a different field than circuit analysis based on Kirchhoff's rules?
 
Last edited:
So a resistor is one branch and two resistors in series still one branch ?
 
Even when you have two series resistors in a "branch"?


In electrical networks almost every component has to have at least two connection points to the network. The main exception that can make do with a single connection is Earth or ground.

When you are programming a computer, you have to tell the computer where these connection points are. This specifies the network to the computer.

Each connection point has to have a name or identifier.

I am calling these connection points nodes and the connections branches.

Normally you specify by what is known as the incidence matrix or a netlist.

The specification of other non electrical networks, eg pipes or roads or structural framworks follows the same pattern, except that some networks can function with only one connection to some components.
 
Studiot said:
Each connection point has to have a name or identifier.
I am calling these connection points nodes and the connections branches.
Normally you specify by what is known as the incidence matrix or a netlist.
OK, so we were talking about two different things. The "classical" Kirkchoff's rule "nodes" are a little different. I suppose it is left to OP to specify what is his actual problem.
 
This thread is a spin off from another about this by nebbione, where he clearly indicates he wants to use matrix methods.
Classic Kirchoff is not a matrix method.

https://www.physicsforums.com/showthread.php?t=641568

As a matter of interest, how would you define the branch currents in Maxwell's mesh method?
 
  • #10
Studiot said:
This thread is a spin off from another about this by nebbione, where he clearly indicates he wants to use matrix methods.
Classic Kirchoff is not a matrix method.
OK, I had no idea about the other thread. Sorry for my interventions.
 

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