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Solution: In the following figure, the configuration of resistors is k...

Question

In the following figure, the configuration of resistors is known as a Wheatstone Bridge, which is used to measure the resistance of an unknown resistor (let's say R1 in our case). This is accomplished by varying the resistance of one of the outside resistors (let's say R5 in our case) until the resistance through the center of the bridge is zero. For our bridge, the battery produces 20 V and the fixed resistances are R2 = 10 Ω, R3 = 20 Ω, and R4 = 30 Ω. If the current through the center of the bridges is zero, and the current produced by the battery is 1 A, when R5 reaches a value of 15 Ω, what is the unknown resistance?