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The equivalent resistance between A and B of the network shown in figure [Figure: from A, resistor R goes to node P and resistor 2R goes to node Q. 9R joins Q to P. 3R joins P to B and 6R joins Q to B.]

Asked in JEE Main 1st Feb 1st Shift 2023 · Wheatstone bridge

Figure: Wheatstone bridge
Answer: (3) 8/3R

Step-by-step solution

This is a bridge: arms R (A to P), 2R (A to Q), 3R (P to B), 6R (Q to B), with 9R between P and Q.

R/(3R)=(2R)/(6R)=1/3, so the bridge is balanced and no current flows in 9R.

Remove 9R: (R+3R)∥(2R+6R)=4R∥8R

R_AB=(4R×8R)/(12R)=8/3R

Why the other options are wrong

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