![]() ![]() The potential across every resistor in the bridge equals the product of the current flow and resistance across it. So, the current flow across PQ and PR is I 1 and the current flow across PS and RS is I 2.Īs per KVL (Kirchhoff’s voltage law), the voltage drop in the closed-loop is ‘0’ which means the voltage across the loop PQSP is ‘0’. Wheatstone Bridge Derivationįor the balanced Wheatstone bridge, there is no current flow across the galvanometer and at this point I G = ‘0’. The bridge holds increased reliability and gives precise outcomes. The arms QS and PR are considered as conjugating arms for the bridge due to the reason that when the Wheatstone bridge is in a balanced condition, and if the positions of battery and galvanometer are swapped, then this is shown no impact on the balanced state. This corresponds that at the points Q and S, the voltage level is the same. So, in this condition, the difference of voltage between Q and A is ‘0’. We know that a galvanometer is connected between Q and S, and when there is a flow of zero current through it, the bridge is considered to be in a balanced state. This is the construction of the Wheatstone bridge.Īs discussed, the Wheatstone bridge works on the principle of null deflection. The amount of current that flows through the galvanometer is known by the level of potential difference which is applied to it. The source connected between P and R points is the electromotive source. And in between the other two points (Q and S), a galvanometer is connected to know the current values. As per the above picture, a voltage source is connected between two points (P and R) which are diagonally opposite to each other and this is considered as battery arm. The device consists of four resistors named R A, R B, R C, and R D. The below picture shows the fundamental Wheatstone bridge circuit. ![]() It also includes an EMF source and a galvanometer. The instrument consists of four arms where three arms have variable resistance, two known resistance, and the other arm consists of unknown resistance (to be known). The device was initially built to know the unknown resistance values, whereas it can also be utilized to standardize devices such as ammeters, voltmeters, and others using a variable resistance. The instrument operates in a similar way to a potentiometer, and this is mainly employed to measure medium resistance values and to know the high resistance values, a sensitive ammeter is also placed in the circuit. This device functions on the null deflection principle which means that the resistances ratio is equal and there is no current flow across the galvanometer. By comparing with the value of known resistance, the unknown value is calculated. The instrument that is employed to know the unknown resistance through comparison procedure is termed as Wheatstone bridge. ![]()
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