Find the equivalence resistance for the circuit

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Usman Ashraf

Joined Jul 30, 2017
7
Kindly explain how to solve the following network. The answer is 6 ohms and independent of R2. Can anyone explain that?

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GopherT

Joined Nov 23, 2012
8,012
Kindly explain how to solve the following network. The answer is 6 ohms and independent of R2. Can anyone explain that?
Remove R2 and you'll see two parallel sets of 6 ohms (3 + 3) in parallel. If you have two resistors (6 ohms each), I can assure you that the equivalent resistance is NOT 6 ohms for the full circuit.

Tonyr1084

Joined Sep 24, 2015
7,106
Can you solve it now ? ? ?

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Dodgydave

Joined Jun 22, 2012
10,514
3 ohms...

Tonyr1084

Joined Sep 24, 2015
7,106
3 ohms...
That's what I'm seeing. Just how the TS knows it's 6Ω is beyond me. Maybe it is. I've always been good at math. There's NO equation I can't screw up!

Tonyr1084

Joined Sep 24, 2015
7,106
I'll give you a hint: There's no current flowing through the 400Ω resistor.

Thread Starter

Usman Ashraf

Joined Jul 30, 2017
7
Remove R2 and you'll see two parallel sets of 6 ohms (3 + 3) in parallel. If you have two resistors (6 ohms each), I can assure you that the equivalent resistance is NOT 6 ohms for the full circuit.
Thanks for the reply. Yes, I just misquoted it. The answer is 3 ohms. Really sorry for that. But can you explain how do we arrive at 3 ohms.

Thread Starter

Usman Ashraf

Joined Jul 30, 2017
7
Kindly explain how to solve the following network. The answer is 6 ohms and independent of R2. Can anyone explain that?
The answer is 3 ohms. Sorry for misquoting.

Thread Starter

Usman Ashraf

Joined Jul 30, 2017
7
Thanks for the reply. Yes, I just misquoted it. The answer is 3 ohms. Really sorry for that.

I understand it now. You guys are real genius!

Tonyr1084

Joined Sep 24, 2015
7,106
As I gave you the hint before, the 400Ω resistor has no current. Therefore no voltage. No voltage, no current no apparent resistance. In other words the 400Ω resistor is just a goldbrick circuit. It does nothing to the values.

SO: You have two 3Ω resistors in series - effectively creating a 6Ω resistor. You have a second set of resistors constituting another 6Ω resistor. Two 6Ω resistors in parallel equate to 3Ω. Do you understand how we come up with 3Ω?

Thread Starter

Usman Ashraf

Joined Jul 30, 2017
7
Can you solve it now ? ? ?View attachment 131895
Yes, I can see that there is no potential difference across 400 ohms. So we eliminate it from the circuit and solve. Is that right?

Tonyr1084

Joined Sep 24, 2015
7,106
Yes, that's right. It's a goldbrick. Made to make you chase it for no good reason.

Thread Starter

Usman Ashraf

Joined Jul 30, 2017
7
As I gave you the hint before, the 400Ω resistor has no current. Therefore no voltage. No voltage, no current no apparent resistance. In other words the 400Ω resistor is just a goldbrick circuit. It does nothing to the values.

SO: You have two 3Ω resistors in series - effectively creating a 6Ω resistor. You have a second set of resistors constituting another 6Ω resistor. Two 6Ω resistors in parallel equate to 3Ω. Do you understand how we come up with 3Ω?
Yes, I am 100% clear. Thanks.
I must say you guys are great people.
Are you paid for this?

Tonyr1084

Joined Sep 24, 2015
7,106
If I were paid it'd probably be 20¢. Used to be 2¢, but given inflation - - - .

But no, we're not paid. Just that some of us are loud mouths and like to help others.

KeepItSimpleStupid

Joined Mar 4, 2014
5,088
Nice job. You can also solve it with 3 loop equations. Set I1, I2 and I3 as clockwise loop currents from left to right, top to bottom.

I changed the I to Y.

e.g.
3Y1+400*(Y1-Y2)+3Y3=0
2 more eqns

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Thread Starter

Usman Ashraf

Joined Jul 30, 2017
7
This thread is solved and closed. Thanks!

WBahn

Joined Mar 31, 2012
27,486
MOD NOTE: Moved to Homework Help. Closed per TS's request.

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