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Need help figuring this circuit

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hi,
LTspice indicates why there is a difference.
 

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Sorry sir but I don't understand.. ? where is there a differance and why :\

hi,
The LTS 7031R value is very close to the multisims 7026R, sims use more precise calculations than we do.

Your answer of 6350R is incorrect, try to redo the sums.
 
Well my answer has to be correct because when we did the lab, all my values were good.

And before doing it with real resistors, we had calculated 6.35k.

What is LTspice ?
 
I just run it in multisim 8, and I get 7032 Ohms, which I believe is as good as identical to ericgibbs result with LTS
 

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Try redo-ing your calculations. Your equation in your first post seems to be correct. I plugged the values in and worked it out on a calculator. My answer is 7.032k.
 
...

And before doing it with real resistors, we had calculated 6.35k.

What is LTspice ?

LTSpice is the best free circuit simulator available on the web; better than ones that charge $20000

I put the network into LTSpice, and force 1Adc through the network. Since the voltage at Node 4 is 7031.87V, then it follows that the equivalent resistance from N4 to GND is 7031.87V/1A = 7031.87Ω
 

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You can get readout directly in Ohms by doing the math in the waveform display. This can be done with either a voltage source or a current source. Of course, it is no better than Mike's method, but it is interesting that the display will plot resistance on the vertical axis.
And, it is handy for plotting impedance between nodes in a circuit.
 

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Thank you

but, software aside, on paper with a pen and a calculator... how would you approach the config eq for the Rt ?

I see it as (((R1//R2)+(R3//R4))//R7)+(R5//R6) but I can be wrong ?
 
With my "paper & pen" (actually excel spreadsheet) it is 7031.87384179803Ω using your equation, which is correct. It's all about the number of decimal places used.
 
That's weird because my 6.35k value was correct according to the teacher and my classmate. There's no way a decimal could cause a 682 ohms differance..
!
 
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That's weird because my 6.35k value was correct according to the teacher and my classmate. There's no way a decimal could cause a 682 ohms differance..
!

hi,
Step by step.....

(((R1//R2)+(R3//R4))//R7)+(R5//R6)

R1 || R2 = 10476.2R

R3 || R4 = 5003.8R

R5 || R6 = 956.5R

10476.2R + 5003.8R = 15480R

So R7 || 15480R = 6075.4R

So 956.5R + 6075R = 7031.5R QED
 
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That's weird because my 6.35k value was correct according to the teacher and my classmate. There's no way a decimal could cause a 682 ohms differance..
!
You really need to tell the teacher and your classmate that they are wrong. It would be interesting to see what the mistake was that each of you made.
 
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Please throw me a log in the face.

R5 is actually 2.2k, not 22.

And I've spent hours on it because of that stupid mistake of mine. I was so ashamed and discouraged for nothing.
 
(((R1//R2)+(R3//R4))//R7)+(R5//R6)

R1 || R2 = 10476.2R

R3 || R4 = 5003.8R

R5 || R6 = 956.5R

10476.2R + 5003.8R = 15480R

So R7 || 15480R = 6075.4R

So 956.5R + 6075R = 7031.5R QED


Here are a few more decimal places...

R1 || R2 = 10476.2R 10476.1904761905


R3 || R4 = 5003.8R 5003.80228136882


R5 || R6 = 956.5R 956.521739130435


10476.2R + 5003.8R = 15480R 15479.9927575593


So R7 || 15480R = 6075.4R 6075.3521026676


So 956.5R + 6075R = 7031.5R QED 7031.87384179803
 
Here are a few more decimal places...

R1 || R2 = 10476.2R 10476.1904761905

R3 || R4 = 5003.8R 5003.80228136882


R5 || R6 = 956.5R 956.521739130435


10476.2R + 5003.8R = 15480R 15479.9927575593


So R7 || 15480R = 6075.4R 6075.3521026676


So 956.5R + 6075R = 7031.5R QED 7031.87384179803
What's the point?
 
Are 10 digits after the decimal point so accurate ? On resistors with like 10 000 ohms, I would think that the pico values are washed away by the % of precision of that resistance by far.

If the resistors have a 1% error margin, the resistors of ' R1 || R2 = 10476.2R 10476.1904761905 ohms ' could vary of 104,761904762 ohms lol
 
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