Find the equivalence resistance for the circuit

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GopherT

Joined Nov 23, 2012
7,983
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.
 

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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
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
3,584
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
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
3,584
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.
 
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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