Wheatstone Bridge

A Wheatstone bridge is a circuit-based instrument used to measure an unknown electrical resistance precisely by balancing two legs of a bridge circuit, one containing the unknown resistor and the other containing known and adjustable resistors, until a galvanometer connected across the bridge reads zero current, at which point the unknown resistance can be calculated from the known values. The device takes its name from the British scientist Charles Wheatstone, who popularized and improved the circuit in 1843, although the underlying bridge configuration had been described earlier by Samuel Hunter Christie in 1833. Because balancing the bridge to a null reading avoids the calibration errors inherent in reading a meter directly, the Wheatstone bridge became a standard precision instrument in electrical laboratories and industry for measuring resistance and, in modified forms, related quantities such as capacitance, inductance and strain.