Wheatstone Bridge essays

Wheatstone Bridge essays The most accurate measurements of resistance are made with a galvanometer (or a voltmeter) in a circuit called a Wheatstone bridge, named after the British physicist Charles Wheatstone. This circuit consists of three known resistances and an unknown resistance connected in a diamond pattern. A DC voltage is connected across two opposite points of the diamond, and a galvanometer is bridged across the other two points. When all four of the resistances bear a fixed relationship to each other, the currents flowing through the two arms of the circuit will be equal, and no current will flow through the galvanometer. By varying the value of one of the known resistances, the bridge can be made to balance for any value of unknown resistance, which can then be calculated from the values of the other resistors. In theory, if one arm of an originally balanced equal-arm Wheatstone Bridge is changed from R to R + R, the bridge voltage will be given by: V0 = (Vs/4) x (R/R) = (Vs/4R) x R Therefore, when plotting the graph V0 against R, the values R around less than about 10Ù we would expect a linear slope. For the larger values we will get a definite curve. In this experiment we will use the same technique to analyse and determine the out-of-balance voltage due to the change in resistance. The out-of-balance voltage is a measure of the change in resistance, which is thus made to be proportional to the external influence. Similar bridges, substituting known inductances and known capacitances for the resistance arms of the bridge, are employed in the measurement of the inductance and capacitance of circuit components. Bridges of this type are usually known as AC bridges, because AC sources are used rather than DC sources. To observe features of the out-of-balance voltage of an initially balanced Wheatstone Bridge. Â ¡ 4 known resistors (4 x 100Ù resistors) Â ¡ Decade box r...