Hi, it's been a long time since I did any physics, and electricity was never my strong point. I've been revising the basics from an experimental standpoint, and I've run into something that I don't understand. I hope someone here will be able to help. I have a 75W 120V light bulb, which I expect (by calculation) to have a resistance of 192ohms, and hence pass a current of 0.625A when hooked up to a 120V AC supply. I've done that and tested the configuration and my multimeter cofirms that current is being passed. Then, I made the assumption that if I hooked the same light bulb up to a 12V DC car battery, it would have the same resistance, and hence pass a current of 0.0625A. When I hooked it up in that configuration and measured the DC current, I got a measurement of 0.18A, which I think implies a resistance of 66ohms. What is going on here? Does the lightbulb have a different resistance to DC than AC? One thing to note here is that in the 12V DC circuit, the bulb did not light up. Perhaps then this is just shows the temperature dependance of resistance showing up?