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Carbon Bulb vs. Tungsten Bulb | by eschlaep
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Carbon Bulb vs. Tungsten Bulb

This graph shows the resistance of the filament in two types of light bulbs. The blue curve shows that a carbon filament decreases in resistance as the bulb heats up, and the pink curve shows that a tungsten filament bulb increases in resistance as it heats up.

 

Thus, carbon filament bulbs have a negative temperature coefficient and tungsten filament light bulbs have a positive temperature coefficient.

 

Tungsten is the filament material most commonly used in household light bulbs.

 

Incidentally the curve for the carbon filament bulb stops short at 90V because I don't want to damage it. It runs very, very hot!

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Taken on October 15, 2007