To find the unknown resistance,
four resistors are connected in the four arms of the Wheatstone bridge as shown in the figure.
Here R1 and R3 are the known resistances, R2 is the variable resistance, and Rx is the unknown resistance.
The galvanometer is connected between the terminals of D and B to determine the null or balanced condition of the bridge.
We have to vary the variable resistance until the null condition is obtained, at this instant the galvanometer reads zero.
During the null condition, the product of resistances in the opposite arms of the bridge is equal.
In this way, we can find the unknown resistance by using the Wheatstone bridge.
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