- #1

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I have tried with kirchhoff law, but I failed.

thanks

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- Thread starter aaronll
- Start date

Superposition on nodes" , because with that is totally clear.In summary, the conversation is about a student asking for help with a circuit problem and the expert providing guidance on how to use Kirchhoff's laws and delta-Y transforms to solve it. The expert also suggests using the superposition method to simplify the equations. f

- #1

- 23

- 4

I have tried with kirchhoff law, but I failed.

thanks

- #2

Mentor

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- #3

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If I start with these equation, assuming current I_i for i = 1,2,3,4,5, and using KCL and what I know about circuit and correlated laws:

I have:

I_1 + I_2 = I_{tot}

I_1 = I_5 + I_3

I_2 + I_5 = I_4

I_3 + I_4 = I _{tot}

and for general I have:

## R_{tot} = \frac{V_{AB}}{I_{tot}}##

with the equation:

R_1 * I_1 + R_3 * I_3 = V_{AB}

and so on, for total of 4 equation, each equal to V_{AB}

By now, is correct my resolution?

to me seem very strange

P.S. excuse for some LaTex code but seem not work, If you help me also with this :)

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- #4

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[itex]R_{eq}[/itex] = <whatever>

- #5

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Yes, ##R_{tot}## that I have written is the ##R_{eq}##, but to find that resistance... I tried with KCL with that bunch of equation, but I don't arrive at the end because there always too much variable in the equation I found ( e.g. for replacement)

[itex]R_{eq}[/itex] = <whatever>

- #6

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Do you know about delta-Y transforms?

- #7

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According to my professor they come later.. so first I should able to resolve this exercise, but I don't understand howDo you know about delta-Y transforms?

- #8

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Well, since you can't just USE the transform equations, it is now up to you to derive them. This will allow you to break your problem into two parts --- one fairly messy, the transform equations, and the other very simple conceptually but still involving messy equations in this case because you have so many unknowns.According to my professor they come later.. so first I should able to resolve this exercise, but I don't understand how

Take the upper 3 resistors as a delta and convert that to a Y. That's the hard part. Then you have a very simple series/parallel circuit that is algebraically trivial but which will look messy as all get-out in this case because of the 5 unknowns you have to carry around.

The progression will look like this:

Literally speaking, the delta and Y are upside down in this case, but they are still delta and Y in electronics.

- #9

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- #10

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Anyway thanks for the help.

- #11

Homework Helper

Gold Member

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I think the question was asking you, prompting you, to define, that is to write out the equation for equivalent resistance. Just for the sake of a logical and suggestive order of procedure.Yes, ##R_{tot}## that I have written is the ##R_{eq}##, but to find that resistance... I tried with KCL with that bunch of equation, but I don't arrive at the end because there always too much variable in the equation I found ( e.g. for replacement)

Then this definition contained so it's related to things you have already written and you can start to fill in, substitute et cetera. As I said, just one way of proceeding there are more

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- #12

Gold Member

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Can you show us how you did it with "Superposition on nodes" so that when other people search for a solution to this problem in the future they will find your work?

Anyway thanks for the help.

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