A Wheatstone bridge is a null measurement device for accurately measuring resist

Question

A Wheatstone bridge is a null measurement device for accurately measuring resistance (sec figure). By tuning the variable resistor R_3 until the galvanometer G reads zero, the value of the unknown resistor, R_x, can be determined. Since there is no current running through the galvanometer, the two branches of the circuit abc and adc are in parallel with the source. in the bridge shown, this occurs when R_3 = 2550 Ohm. What is R_x, in ohms, if the ratio between the resistances in branch adc of the bridge is R_2/R_1 = 0.657

Explanation / Answer

At null condition of Wheatstone bridge,

we can use formula Rx/R3 = R2/R1

So, Rx = (R2/R1)*R3 = 0.65*2550 =1657.5 ohm

So unknown resistance of resistor Rx is 1657.5 ohm

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