**PURPOSE: **To 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).

**SUGGESTIONS: **

**REFERENCES: ** (PIRA 5F20.40)

**EQUIPMENT: **Two 400 ohm resistors, 0-90 ohm variable resistor, 60 watt light bulb as "unknown" resistor, center zero 0-5 milliamp lecture meter, digital multimeter.

**SETUP TIME: **5 min.