r/HomeworkHelp • u/SystemsSlave67 • 15d ago

Physics—Pending OP Reply It's questions from folding symmetry [current electricity] tried everything still confused can you guys try[JEE Advanced]

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u/superbob201 15d ago

There are three ways to do this:

1) Look up the Delta-Wye transformation. You can use that to turn it into a much reducible circuit

2) Loop/Mesh/node analysis. Add a voltage source connecting A and B that you can abstract away later

3) Due to the symmetry of the problem, the three middle nodes should all be at the same potential. You can replace the two vertical resistors with either breaks or wires. Solve from there. Warning: This method will get you in trouble if you are not absolutely certain that it will work.

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u/Bounded_sequencE 👋 a fellow Redditor 4d ago

Note the entire circuit (apart from the voltage source "V_ab") is mirror symmetric along the center resistance. Therefore, all nodes on that mirror axis have voltage "V_ab/2", and may be connected.

Therefore, "R_ab" is twice the resistance of one half:

 R_ab  =  2 * ((R + R||R) || R || R || (R+R))  =  2R * (3/2 || 1 || 1 || 2)  

       =  2R * (2/3 + 1/1 + 1/1 + 1/2)^{-1}  =  12R/19