Believe your data. The tungsten filament of a light bulb has a resistance that increases with temperature, and as you raise the voltage, the filament becomes much hotter.
Many materials have a resistance that varies with temperture, but the effect is more noticeable with light bulb filaments because they are designed to get very hot, in order to emit light.
I'm doing a report on my experiment right now where you had to test out the voltage and current of 2 resisters and a light globe with an ammeter and voltmeter. We had to graph the results, and the reisistors had a linear relationship between voltage and current, but the light globe is either exponential or power. Can anyone explain why this is? Is it a systematic error?
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So basically, the light bulb's resistance varies?
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