|
|
This topic comprises 2 pages: 1 2
|
|
Author
|
Topic: A frequent(cy) question
|
John Schulien
Expert Film Handler
Posts: 206
From: Chicago, IL, USA
Registered: Nov 1999
|
posted 08-15-2001 04:47 PM
Mark -- I thought that arc lamps needed somewhere around 24-40 volts, not 440. How did they step the DC down to the correct voltage?I just remembered something I did years ago ... I must have been in 7th grade. I had been reading an old "science for boys" book that described how to make a make a carbon microphone using pencil leads. I thought that was pretty cool, and decided to try it. I used a jackknife to whittle away two sharpened pencils near the eraser, and wound wire around the exposed graphite. The idea was that by laying two carbon rods, one on the other, they would pick up vibrations in the air and act as a microphone. I never got the microphone working, but I had another idea. I decided to see what would happen if I passed electricity through the carbon rods. I cut off the plug end of an extension cord, stripped the wires, wrapped each wire around the exposed graphite near the eraser end of each pencil, and placed the pencils in a vise, at about a 90 degree angle, with about a quarter-inch gap. I set things up so that I could pivot the tip of one lead into the tip of the other. Then, I plugged in the cord, and slowly pushed one of the sharpened points towards the other with a scrap of wood ... I wasn't quite expecting what happened next ... Wait, that's an understatement ... I just about jumped through the roof! I don't think I've EVER seen anything as bright as that arc, before or since. The instant the two points came in contact, the entire makeshift apparatus gave off a HUGELY intense white light, and burst into flame! Everything happened in probably two seconds. I remember seeing the arc, and jets of fire and heavy smoke shooting out from inside the pencils. I wanted to unplug the thing, but the plug was on the workbench behind the arc, where I couldn't reach it without reaching through the fireball. Fortunately, at that point, the fuse blew, the arc went out, leaving the pencils burning from end to end, and I was left standing in the dark, the entire basement thick with smoke. Then the smoke alarm went off. Fortunately, I was able to get the windows open and more-or-less air out the basement before my parents got home. They were used to the smell of gunpowder and burning things (yes, I was that kind of kid), so no one ever said anything. That was the end of my experimentation with carbon rods.
| IP: Logged
|
|
|
|
|
|
|
|
|
|
|
|
|
|
Rick Long
Jedi Master Film Handler
Posts: 759
From: Toronto, Ontario, Canada
Registered: Nov 1999
|
posted 08-17-2001 10:03 PM
For anyone who's interested, I found this on the IEEE website;
Why did the US choose 120v for household current and Europe choose 220v? It appears that the 120 were chosen somewhat arbitrarily. Edison came up with a high-resistance lamp filament he thought desirable to keep distribution losses down. In 1882, he applied for patents on a 3-wire system which gave 220v transmission with 110v lamps. Why does US use 60 cycles and Europe use 50 cycles? Many frequencies were used in the 19th Century for various applications, with the most prevalent being the 60 c/s supplied by Westinghouse-designed central stations for incandescent lamps. The development of a synchronous converter which operated best at 60 cycles encouraged convergence toward that standard. Around 1900, the introduction of the high-speed turbine led to settlement on two standards: 25 cycles for transmission and for large motors (this had been a compromise decision at Niagara Falls), and 60 cycles for general purpose systems. Meanwhile, in Germany, AEG -- which used 50 cycles -- had a virtual monopoly, and this standard spread to the rest of the continent. In Britain, differing frequencies proliferated, and Britain only settled on the 50 cycle standard after World War II.
http://www.ieee.org/organizations/history_center/historical_faqs.html
| IP: Logged
|
|
|
|
All times are Central (GMT -6:00)
|
This topic comprises 2 pages: 1 2
|
Powered by Infopop Corporation
UBB.classicTM
6.3.1.2
The Film-Tech Forums are designed for various members related to the cinema industry to express their opinions, viewpoints and testimonials on various products, services and events based upon speculation, personal knowledge and factual information through use, therefore all views represented here allow no liability upon the publishers of this web site and the owners of said views assume no liability for any ill will resulting from these postings. The posts made here are for educational as well as entertainment purposes and as such anyone viewing this portion of the website must accept these views as statements of the author of that opinion
and agrees to release the authors from any and all liability.
|
Home
Is the image of that arc burned into your retinas?
Printer-friendly view of this topic