In general, resistance increases as heat increases. Hence super conductors are kept cold. (Or another way to think of it is, for a single electron, it is easier for it to travel through a crowd of other electrons that aren't bouncing around than it is to go through a crowd of other electrons that are... like a real-life traffic.)
-Mark On Sat, 1 Feb 2003, Peter Jay Salzman wrote: > ach, one more thing. i can't believe i forgot this (but the truth is, > my department knows i hate experimental physics, and has given me > lectures and discussions for the past few years instead of running > labs). > > light bulbs are highly non-ohmic (linear) devices. the power they > consume is highly dependent on the temperature of the filament. in > other words, the power they consume depends on how long they've been > left on. for the life of me, i can't remember whether they consume > more or less power as they heat up. for your sake, i hope it's less. > :-) > > 250W is some kind of average; i don't know how they get that number, but > i'm sure they have some kind of procedure like "leave the lightbulb on > for an hour and divide by 3600" or something like that. > > from what i remember about the physics 9C labs, 25% sounds pretty > reasonable to me. > > pete > > > > > begin Jeff Newmiller <[EMAIL PROTECTED]> > > On Fri, 31 Jan 2003, Rod Roark wrote: > > > > > I got my first electric bill at the new house; looks too > > > high. So I decided to do an experiment. > > > > > > Outside the house is an electric meter. It reads KWH > > > accumulated on 5 dials, and has a horizontal platter that > > > appears to spin about 100 revolutions per KWH (anyone know > > > if this is exactly true for a standard meter?). > > > > > > So I figure that means 10 watt-hours per rev, or 36,000 > > > watt-seconds per rev. > > > > > > I timed one revolution with most things in the house turned > > > off. 45 seconds. Then I turned on a 250W light bulb and > > > timed it again. 32 seconds. So: > > > > > > 36,000 watt-secs / 45 secs = 800 watts > > > 36,000 watt-secs / 32 secs = 1125 watts > > > > > > 1125 - 800 = 325 watts -- for a 250W bulb. > > > > > > How come? Should I complain to PG&E, or is there some > > > gotcha that I'm missing? > > > > Go look on your meter face for a number labelled Kh. A typical value is > > 7.2. Units are Watt-hours per revolution. > > > > Count the number of seconds (S) it takes for the disk to revolve once. (I > > usually time two or three turns and average. Total measurement intervals > > between 40 and 90 seconds will usually give good results (though if it > > spins three times you will need to remember to divide the total interval > > by three before using the answer). > > > > Power = Kh * 3600 / S > > > > The only difference between your equation and mine is your use of Kh=10. > > > > Assuming you have a regular meter like mine, the calculation should yield > > 810W - 576W = 234W, which could be reasonable. I don't know what kind of > > light bulb you used... torchiers output is often adjustable. Beware of > > "hidden loads" too... a refrigerator kicking off or on toward the end of > > your measurement interval can reduce or increase respectively your > > apparent load. > > > > For those looking to check these answers: the energy meter is almost > > certainly more accurate than whatever test equipment the average computer > > geek is likely to have laying around for measuring energy consumption > > (energy meters have a tested accuracy of <0.3%). P=V*I always for > > simultaneous/instantaneous measurements, but the root-mean-square readings > > typically reported by DVMs ONLY hold for _sinusiodal waveforms that are in > > phase_. Those conditions are often not valid in the real world, so beware > > of getting out your DVM to double-check your energy meter. :) > > -- > First they ignore you, then they laugh at you, then they fight you, > then you win. -- Gandhi, being prophetic about Linux. > > Fingerprint: B9F1 6CF3 47C4 7CD8 D33E 70A9 A3B9 1945 67EA 951D > _______________________________________________ > vox-tech mailing list > [EMAIL PROTECTED] > http://lists.lugod.org/mailman/listinfo/vox-tech > -- Mark K. Kim http://www.cbreak.org/ PGP key available upon request. _______________________________________________ vox-tech mailing list [EMAIL PROTECTED] http://lists.lugod.org/mailman/listinfo/vox-tech
