Recent content by tdaffin

Hi, I have an apparatus which I'm using to electrolyse water into a mixture of hydrogen and oxygen. I'm attempting to do some calculations based upon measurements I've made. What I want to do is come up with a Joules per Litre figure for energy consumed to evolve a volume of the mixed gas...

Ok, thanks. I'll consider that the last answer then. So, I shall not be using my Multi-meter to measure resistances in any energised circuits.

Ok, thanks for clearing that up. I understand now that it's a bad idea to hook the DVM up in series when it's in resistance mode. Is it possible to use the DVM in parallel across the component in resistance mode when the circuit is powered up? One thing that springs to mind for me is that I...

Yes, thanks waht, this also fits with the bulb having a lower resistance again when no voltage is across it at all (measuring it using the ohmmeter). I guess that even though it's not hot enough to produce light with 12v across it that it has heated up above room temperature -- enough to raise...

Well, thanks again everyone... I was going to go home and put my ohmmeter across the live bulb! Thanks to berkeman for informing me that the ammeter will have a series resistance -- I have two multimeters so I can use one to measure the resistance of the other when it's an ammeter. Thanks also...

Thank you both for your help! I guess I need to devise a method to measure the filament temperature in all 3 circumstances and then plot that vs. the resistance. If it comes out logarithmic (with 3 data points, that won't be so convincing -- just not linear), I'll rest my case for now.

One more thing... I went back to the garage after posting this and measured the resistance of the bulb and got 13ohms. So, now we have 192ohms(calculated) @120v (illuminated), 66ohms @12v (no illumination) and 13ohms @ 0v (room temperature). I guess it would help if I could get a temperature...

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...