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How do you find the equivalent resistance here?

How do you find the equivalent resistance here? (I realized it's a Wheatstone bridge, but it's unbalanced, so that doesn't help.) I tried using Kirchhoff's laws, but there is no cell given.

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  • \$\begingroup\$ No. Just practising, \$\endgroup\$ – Leponzo Nov 26 '14 at 17:21
  • \$\begingroup\$ This might help you: en.wikipedia.org/wiki/… \$\endgroup\$ – Null Nov 26 '14 at 17:32
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    \$\begingroup\$ If you connected +1V to point X and 0V to point Y how much current would flow? If you can work out the answer to that then you can work out the resistance between X and Y. \$\endgroup\$ – JIm Dearden Nov 26 '14 at 17:36
  • \$\begingroup\$ This combination consists an unbalanced Weaston bridge, so there is a current from B to E and definately you can not solve with series/parallel method. You can use mesh analysis or Y-Δ transform en.wikipedia.org/wiki/Y-%CE%94_transform. Another interesting proposal is here physics.stackexchange.com/questions/22252/… but it is not proofed by anyone yet \$\endgroup\$ – GR Tech Nov 26 '14 at 21:04
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It looks like irreducible network - network which does not contain series or parallel connections that can be reduced.

You can add some voltage source to X and Y terminals and do mesh analysis.

It is explained in Wikipedia mesh analysis article, and also in this video by Darryl Morrel so I will not explain it here.

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  • \$\begingroup\$ This can be found pretty easily using delta-to-wye transformations. \$\endgroup\$ – Eric Nov 26 '14 at 17:39
  • \$\begingroup\$ Yea, but I saw that Null suggested that in comments, so I provided diffrent (more universal) approach. \$\endgroup\$ – Kamil Nov 26 '14 at 17:48
  • \$\begingroup\$ @Leponzo I added youtube link to really nice tutorial about mesh analysis. \$\endgroup\$ – Kamil Nov 26 '14 at 21:43
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Use Y-Δ transform and find 7 Ohm.

schematic

simulate this circuit – Schematic created using CircuitLab

After applying the transform technique for R1, R3 and R4, the circuit is as follows:

schematic

simulate this circuit

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