Find the effective resistance between P and Q in the given circuit?

Question

Figure is given on
http://serv2.imagehigh.com/imgss/3990365_IIT.jpg


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Answer 1

Make point Q the common reference for all measurements. Apply a potential at point P. The potential at points A, B, and C will be the same (namely, 1/2 of the potential P to Q) so there will be no current flow thru the 'vertical' resisters labeled 2R and they can be ignored. The top and bottom branches will then have series resistance of 4R and the middle branch will have total resistance of 2R. The total resistance is then
Rt = 1/((1/4R) + (1/4R) + (1/2R)) = R


Doug

Answer 2

hi there. here's the explanation.

the resistors across AB and BC are what you call a wheatstone bridge. basically, the potential drop across is the same such that those 2R resistors become negligible. hence, resistance of the top branch=4R, resistance across the middle branch=2R, resistance across the bottom branch=4R

therefore,

1/Rt = 1/4+1/2+1/4
Rt=1Ohm