The Wheatstone bridge circuit is a diamond-shaped arrangement of four resistors. It has two parallel legs and each leg having two resistors in series. A third leg connected between the two parallel legs at some point within the legs, as drawn in figure. Among the four resistors, one resistance value can be determined by balancing the two legs. Out of four resistors, the value of two resistors R_{1} and R_{3} are known, the value of R_{2} is adjustable, and the value of R_{x} is to be calculated. Then this adjustment is connected to electric supply and a galvanometer between terminal D and terminal B. Now the value of an adjustable resistor is adjusted until the ratio of the two branches resistances become equal i.e. (R_{1}/ R_{2}) = (R_{3}/R_{x}), and galvanometer reads zero as current stop flowing through the circuit. Now the circuit is balanced and the value of the unknown resistor could be measured easily. The reading of the R_{3} decides the direction of the flow of current.

The basic principle of the bridge is to compensate the positive angle phase of the unknown impedance with the negative phase of a capacitance by putting it in opposite branch. By doing so, the potential difference across the detector will become zero and no current will flow through it. The capacitor C_{4} and resistor R_{4} are connected in parallel and the value of both are adjusted so that bridge get balanced.

To balance the bridge by steady current, variable resistance r is adjusted and AC source is replaced by battery and headphone by moving coil galvanometer. Once the bridge is balanced the potential at the terminal D is similar to the potential at E. the flow of current in respective branches are denoted by I_{1}, I_{2}, and I_{3} as shown in the figure.

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