Finding the total resistance of a complex combination

hms.tech

b]1. The problem statement, all variables and given/known data[/b]

Find the total resistance of this complex combination of resistors.
[

2. Relevant equations

R(total)= (Rr)/(R+r)

3. The attempt at a solution

resistance of r(2) and r(3) = 20Ω
resistance of the combination of r(1) and the resultant 20 Ω(ie r(2) and r(3) ) = 20/3
resistance of r(3) and r(5) = 20Ω
resistance of te combination of r(4) and the resultant 20 (ie r(3) and r(5) ) = 20/3

I can't deduce and answer from the above (correct) results.

Need urgent Help !!

tiny-tim

hi hms.tech!

have you tried using Kirchhoff's rules?

hms.tech

No!
Would you kindly guide me how and where do we apply them in this situation.

(i know what they are but am confused about thier appropriate application in this design of resistors)

tiny-tim

hi hms.tech!
just label the currents I₁ I₂ I₃ I₄ and I₆ (with arrows of course!), do KVL and KCL, then find the total voltage drop between A and B, and divide by I₆ …

what do you get?

hms.tech

as i said, i am confused about the way to apply these laws in this unusual situatuion
your 2nd answer did not help any more than the first one (@tiny tim).

Kind Sir, will elaborate on the proposed method.
to put it simply, i am unable to find the voltage drop between A and B.

gneill

Stick either a voltage source or a current source at terminals AB. If it's a current source, find the voltage drop across AB. If it's a voltage source, find the current it's driving into the circuit. Either way the overall resistance of the circuit will be the ratio of the voltage to the current that the source delivers.

Drao92

http://en.wikipedia.org/wiki/Y-%CE%94_transform
This is how you gona solve it.
1,2 and 3 are in triangle, same 3,4,5, change one combination with triangle-star transform and its solved.
My result is 10 ohm.
With kirchhoff.
Lets make I6=10 (you can give it any value you want)
Now, when the current is at A it will be divided by 2, because R1=R2, I3=0 from KCL.
So I1=5, I2=5, i4=5, i5=5.
Now, what you gona do its to KVL in loop 1 (yellow) to find Uab.
After finding Uab, Rab=Uab/I6.
http://www.physicsforums.com/attachm...1&d=1331595516

Attached Thumbnails

 

SammyS

This circuit can be analyzed by the use of symmetry.

An equivalent circuit to this is on with A at one corner of a square, and B at the opposite corner.

Label the other two corners C & D respectively, the corners being labeled: A, C, B, and D in a clockwise sense.

Resistor 1 connects corners A and C.

Resistor 2 connects corners A and D.

Resistor 5 connects corners C and B.

Resistor 4 connects corners D and B.

Resistor 3 connects corners D and C.