A Wheatstone bridge is an instrument that measures an unknown electrical resistance. This is accomplished by balancing the two legs of the circuit, with one of them containing the unknown resistor . When the bridge is perfectly balanced, the voltage across the galvanometer is zero and therefore no current flows between the midpoints. This Demonstration allows you to visualize the Wheatstone bridge circuit and to determine the unknown resistance by changing the resistance of variable resistor .
Move the slider to change the resistance of . (You may need to open the slider to get fine control; click the plus sign.) When both the voltage and the current through the midpoints are zero, the "calculate " button becomes active. Click it to display the value of . Click the button "new calculation" to begin a new problem. You can modify the voltage of the power supply and the resistance of the galvanometer. The sizes of and vary according to their resistances.