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World's Most Exciting Chemistry Movies
Michael Buckbee writes: "After Dan's page got too slashdotted to view, I ran a quick search on Google for more more fun Ferroliquid sites and stumbled into a collection of movies that I wish had been taken in my chemistry classes. Almost all of the experiment descriptions lean heavily on the phrase "EXTREME DANGER" and many contain other fun words like: "Explosion", "Toxic", "Detonation", and "Diazotization"."
Well You could have knocked me down with a feather.
Na Cl
Need a light, Salted
Dude, F=BLI. There's no squaring at work here. You'll need 100's, if not K and M amps to do anything resembling a railgun.
:).
But, P=I^2R. Your Joule heating will be considerable. You'll need some good engineering so that your toy won't disintegrate itself.
And V=LdI/dT. You'll need city bus size capacitors and hydrogen thyratrons to switch massive currents quickly. For railguns we're talking mega-amps in 20 nanoseconds.
Depends on what you call a "railgun".
If you're trying to make a small water fountain, you can get away with a newton of force or less. You'd also be working in continuous mode, which means a capacitor bank isn't needed (just a DC or approximately DC power supply that can provide the needed current).
One-tesla magnets are easy to buy or build - about one tesla is the saturation point of most ferromagnetic materials, so a chunk of iron will turn a 0.01-T or 0.001-T solenoid into a 1T magnet in short order (depending on the permeability of garden-variety scrap iron).
Similarly, high-strength permanent magnets will be in the Tesla range (probably more like half a tesla, but still strong enough for our purposes).
At one tesla, for a force of 1N, and assuming a water tube 1 cm wide, a current of 100 amps is adequate. A step-down transformer, a bridge rectifier, and a wall plug, and you're there.
For a proof-of-concept tabletop railgun, you can similarly relax constraints. If I'm trying to fling, say, a 10g segment of copper plumbing pipe across a room, I don't need a capacitor bank - I need a marine battery. If I can fire the projectile at 10m/s, that gives me a good 5m or so before it hits the floor from tabletop height (10m if I fire it at an angle instead of level); more than enough for a party trick. At that low a speed, it's in the railgun for tens of milliseconds or longer - I don't need nanosecond discharge circuitry. My hypothetical 10g projectile would have a kinetic energy of about half a joule, which means that if my railgun is about a foot and a half long, I again need only 1N of force. A marine battery can supply the required 100 amps of current without any problems at all (in fact, I'd want to drop a resistor in series with it to make sure it doesn't supply much more than that when I short the railgun across it).
Preventing the slug from spot-welding itself to the rails is left as an exercise for the reader
In summary, while I'd need heftier electronics to build a military-grade weapon, tabletop railguns and similar motor-principle conversation pieces aren't that hard to build.
[Aside: I'd actually build a coilgun instead of a railgun if I wanted a military-grade weapon. Much, much easier to build at high power than an ultra-high-current railgun (it's just a series of high-power RF or IF coils repelling the slug with induced currents). Even here, millisecond-level timing is perfectly adequate.]