Hi, I\'m completely bewildered with this problem. The question is A circuit is c

Question

Hi, I'm completely bewildered with this problem. The question is A circuit is constructed with five resistors and a battery as shown. The battery voltage is V = 12.0 V. The values for the resistors are: R1 = 76.0 ?, R2 = 149.0 ?, R3 = 169.0 ?, and R4 = 121.0 ?. The value for RX is unknown, but it is known that I4, the current that flows through resistor R4, is zero. Find R1.

Ok,I think the thing I'm having the biggest trouble with is how the current travels through the circuits. I know that 1 and 3 are in a series, therefore I1 must equal I3. The same goes with 2 and X. I can't figure out how to relate the two lines of charge, with R4. I thought that since R1 and R2 were parallel and the power reaches them first, that V1 would equal V2 which I thought would be 12. However the problem asks me to see what happens after the charge leaves 1, which I have no idea. We are using the smart physics book, and it sucks... They leave out so much.

Explanation / Answer

From wheatstonebridge principle :(read from http://en.wikipedia.org/wiki/Wheatstone_bridge) we get : r1/r2=r3/rX so 76/149=169/rX so rX=331 Now u can solve i think

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