Non-Ohmic Device - Light Bulb


To show the change in resistance of a light bulb with temperature.


Mounted light bulb with double-pole double-throw switch and digital meter.


Setup Time

5 min.




    A 60 watt light bulb is connected to a switch so that it can be quickly disconnected from the 110 VAC◙power to an ohmmeter. The resistance of the 60 watt bulb in operation at a high temperature is R = V^2/P = 110^2/60 = 200 ohms. The resistance cold is about 18 ohms. Turn the bulb on, then switch it to the ohmmeter. The resistance starts high and drops quickly as the bulb cools.