PURPOSE: To show the change in resistance of a light bulb with temperature.
DESCRIPTION: 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.
SUGGESTIONS:
EQUIPMENT: Mounted light bulb with double-pole double-throw switch and digital meter.
SETUP TIME: 5 min.
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