We have learned before how to measure the resistance using a voltmeter and a current meter. The accuracy of such measurements is limited by the internal resistances of these meters. Ideally, we need the internal resistance of a voltmeter to be infinity, and that of an ammeter to be zero. But that is not possible and all the measurements with these meters will have unavoidable instrumental errors.
In this experiment we will learn a way to measure the resistance precisely by using an equipment called Wheatstone Bridge, which is invented by Samuel Hunter Christie in 1833 and improved and popularized by Sir Charles Wheatstone in 1843．
three ZX21A Resistance boxes; one unknown resistor; 85C1 sensitive galvanometer; QJ2002A DC stabilized voltage power supply; switches; wires