Purpose:Demonstrate operation of a Wheatstone bridge.
Description:A Wheatstone bridge is connected as in the circuit below using two (approximately) 400 ohm resistors, a 0-90 ohm variable resistor and a 60 watt light bulb (16.7 ohms cold) with a 6 volt battery and a 0-5 mA ammeter (large lecture meter). The unknown resistance Rx (the light bulb) is:
Rx = Rs (R2/R1),
where Rs is the resistance of the active part of the variable resistor (equal to the fraction of its length used multiplied by 90 ohms).