Engineering Find the resistance R in this network

AI Thread Summary
The discussion revolves around finding the resistance R in a complex circuit. The original poster struggles with calculations and is advised to provide clearer images and detailed steps of their work for better assistance. Key points include the misinterpretation of the current source's resistance and the unnecessary use of the Y to Δ transform. Participants emphasize the importance of showing calculations rather than just listing steps to identify errors. Ultimately, the correct approach involves recognizing the current source as an open circuit and simplifying the circuit accordingly.
Edy56
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Homework Statement
I am supposed to find the equivalent to R2 and I got 2, but I am supposed to get 3
Relevant Equations
None
IMG_20230209_020632.jpg
IMG_20230209_020635.jpg
 
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Welcome to PF. :smile:

It's pretty hard for me to read your uploaded pictures. Can you post a better picture of the original circuit, and type some of your work into the forum so it's readable? Thanks.

(you should consider learning to post math using LaTeX -- see the "LaTeX Guide" link below the Edit window)
 
berkeman said:
It's pretty hard for me to read your uploaded pictures. Can you post a better picture of the original circuit, and type some of your work into the forum so it's readable? Thanks.
what he said (very small).jpg
 
berkeman said:
Welcome to PF. :smile:

It's pretty hard for me to read your uploaded pictures. Can you post a better picture of the original circuit, and type some of your work into the forum so it's readable? Thanks.

(you should consider learning to post math using LaTeX -- see the "LaTeX Guide" link below the Edit window)
the circuit:
ed.png

here is what I did:
(english is not my first language so sorry if i get any terms wrong)
I thought R3, R4 and R5 form a triangle so I turned it into a star for easier calculation and I did the same for R6 R7 and R1.
Then I thought R34 and R35 are parallel so I calculated that too and the same I did for R61 and R71.
Then I thought all of them were connected in order meaning I could add them all together.
That is:
R3435 +R45 + R67 + R6171.
I got the answer 2, I need to get 3.
Where did I go wrong?
 
How could we possibly know where you went wrong when you have not shown your work ???

SHOW EVERY STEP
 
phinds said:
How could we possibly know where you went wrong when you have not shown your work ???

SHOW EVERY STEP
It's at the beginning of the thread
 
Edy56 said:
It's at the beginning of the thread
Yes, and it got this response:
berkeman said:
It's pretty hard for me to read your uploaded pictures. Can you post a better picture of the original circuit, and type some of your work into the forum so it's readable? Thanks.
TYPE your work into the thread.
 
Edy56 said:
the circuit:
View attachment 321978
here is what I did:
(english is not my first language so sorry if i get any terms wrong)
I thought R3, R4 and R5 form a triangle so I turned it into a star for easier calculation and I did the same for R6 R7 and R1.
Then I thought R34 and R35 are parallel so I calculated that too and the same I did for R61 and R71.
Then I thought all of them were connected in order meaning I could add them all together.
That is:
R3435 +R45 + R67 + R6171.
I got the answer 2, I need to get 3.
Where did I go wrong?
That's what I did here?
 
Edy56 said:
That's what I did here?
No, you listed the steps you did not show any of the calculations.

THIS:
"I thought R3, R4 and R5 form a triangle so I turned it into a star for easier calculation and I did the same for R6 R7 and R1."

is a set of steps. It is not calculations.
 
  • #10
phinds said:
No, you listed the steps you did not show any of the calculations.

THIS:
"I thought R3, R4 and R5 form a triangle so I turned it into a star for easier calculation and I did the same for R6 R7 and R1."

is a set of steps. It is not calculations.
I am not sure as to how write that. I can draw it, but I don't know how to write those steps.

If you mean calculating new Rs it's just basic multiplication and I have in the picture.
 
  • #11
I'm sure you could figure out how to type numbers and equations, but I can see that it would be a lot of work. Perhaps someone else here will be willing to look at your hand-written work and follow it to see if they can find your error.
 
  • #12
phinds said:
I'm sure you could figure out how to type numbers and equations, but I can see that it would be a lot of work. Perhaps someone else here will be willing to look at your hand-written work and follow it to see if they can find your error.
Okay
 
  • #13
I cannot read the component values.
R_Values.png
 
  • #15
You do not need the Y to Δ transform.
Current source Ig is infinite resistance, so remove it from the circuit.
Voltage sources, E1 and E2 are zero resistance, so short them.
R1 = R5 = R6 = 2k;
R3 = R4 = 1k;
R7 = 4k.
Series; +
Parallel; //
R16 = R1 + R6 =
R34 = R3 + R4 =
R167 = R16 // R7 =
R345 = R34 // R5 =
R2 = R167 + R345 = 3k.
 
  • #16
Baluncore said:
You do not need the Y to Δ transform.
Current source Ig is infinite resistance, so remove it from the circuit.
Voltage sources, E1 and E2 are zero resistance, so short them.
R1 = R5 = R6 = 2k;
R3 = R4 = 1k;
R7 = 4k.
Series; +
Parallel; //
R16 = R1 + R6 =
R34 = R3 + R4 =
R167 = R16 // R7 =
R345 = R34 // R5 =
R2 = R167 + R345 = 3k.
I am not sure I understand...
The way I do it, I imagine that power is flowing from a to b and so when it's going from a the power splits in two because of R4 and R5 and thus making them parallel. Why isn't it like that?
 
  • #17
Edy56 said:
Why isn't it like that?
Yes, you can do it in the longer way using the inverse Y to Δ transform;
https://en.wikipedia.org/wiki/Y-Δ_transform

Your mistake is that you have the current source, Ig = 0 ohms, as a short circuit, which is wrong. A current source has infinite resistance, which is an open circuit.
You do not need the Y to Δ transform if you make the current source = ∞ ohms.
 
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