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Large electromagnet with unusual requirements

  1. Jul 31, 2016 #1
    I'm trying to build a large electromagnet. It's actually 3 letters, as large as I can get them to be and still work. It's for a scavenger hunt. My dad's an electrician and he says he can't figure out how to make it work, I'm hoping someone has some input.

    The requirements are that it has to pull iron filings toward it from 20'' away and stick to a sheet of paper so that the letters are readable. The sheet of paper is 3'x3' - the letters themselves don't have to be that big but pretty big, depending on what you guys tell me.

    When we tested with a 9v battery, some wire and a nail, we noted that only the exposed ends of the nail attracted any filings and only when we pretty much stuck the nail into the filings... more power I assume is needed, but trying to figure out how to expose enough magnetized metal or material to pull the falling filings toward it...? I am more than happy to put in the dirty work of a lot of wire wrapping etc, I just need to figure out the how. Can anyone help?

    PS: It has to be done by Aug 6 ><
     
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  3. Jul 31, 2016 #2

    etudiant

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    Not easy to do.
    You probably have to separate the problem into a writing component, sort of a magnetic pen that can attract the filings and a holding magnet that actually keeps the filings in the letter shape. The latter should be doable with a letter shaped array of small magnets taped to the back of the paper.
    Pulling filings across 20" is a job for a really large magnet. You might be able to improvise something with an electromagnet spool, put a longer piece of soft iron into the core so the tip of the iron acts as your pen. No clue whether that will work though, just visualizing a magnetic field that reaches out 20" from the end of the pole suggests industrial scale to me.
    You might cheat and have the filings suspended in oil, that eases the friction/sticktion that afflicts heaps of filings, but that gets heavy and messy.
    Maybe something easier to make, something with LEDs for instance?
     
  4. Jul 31, 2016 #3
    Unfortunately it has to be an electromagnet. It doesn't have to write, just display letters (like a sign).
     
  5. Jul 31, 2016 #4

    etudiant

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    The project needs a clever trick just to be feasible, but none have come to me.
    Pulling iron filings from 20" away is really hard, getting a letter shaped magnetic field is inherently very near field.
    You could try to have a big enough electromagnet to pull a wad of filings against the page, with the letters spelled out by little permanent magnets glued to the back of the page. That way the letters would still be spelled out when you turn off the big magnet and most of the filings drop away.

    Alternatively, is it allowed maybe to have the page flat and the letter magnets beneath as before, have a large electromagnet at one end to attract the filings, then tap the paper to help the filings move freely across the page?
     
  6. Jul 31, 2016 #5
    The description says it has to be vertical. However, your thought about possibly having permanent (nonelectric) - that might work. My main concern is like I said above, only the exposed part of the iron nail in my experiment actually attracted anything - how do I get the field to pull toward it in a wide enough range that it would get close enough for the regular magnets to kick in? My tired brain is having trouble figuring out the finer points.
     
  7. Jul 31, 2016 #6

    etudiant

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    A brute force solution with a big electromagnet would probably need for you to go on a scavenger hunt of your own through auto junk yards or maybe some nearby university physics lab looking for some discarded spools of magnet wire with a core, possibly from an old starter motor or discarded experiment. Powering it won't be easy,
    I've built one homebrew with wire around a really big nail. Plugged into an outlet, with a fuse, a rectifier and an in series variable resistor, it worked fine as a magnet and could be used to give things a push or a pull, but it had an action radius of maybe two inches. Twenty inches is a lot harder. Maybe having the iron filings drift down from a couple of feet up so they could be diverted by the magnetic field would work with a weaker field than what is needed to pull the filings across a flat surface.
     
  8. Jul 31, 2016 #7
    Someone has suggested a car battery as a safer alternative to a power source, but I don't know if it'd work. The setup, supposedly, is meant to be a vertical thing with 20 inches between the surface and a funnel through which the filings will fall and (hopefully) be pulled toward the flat surface. I can tape regular magnets to the back of it to try and form the letter shapes if I can get the filings to pull close enough to the paper. (this is not copy paper, it's more like posterboard, attached to a wooden frame to keep it vertical). I... don't know if there is a nearby physics lab. Hm. I will investigate.
     
  9. Jul 31, 2016 #8

    etudiant

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    A car battery is a good source, but please be careful.
    Treat the setup with extra care and have a serious resistor installed. Wear rubber gloves and eye protection. Shorting a battery creates big sparks and high amperage, so risk of serious injury is always there, even excluding the potential for hydrogen explosions or acid spills. These are not benign boxes.
    The setup you describe seems a bit more feasible to me and I wonder whether the 20" gap is between the iron filing drop slit and the flat surface, with the vertical paper for the letters much closer to drop zone. That would perhaps allow a more modest magnet to still be effective.
     
  10. Jul 31, 2016 #9
    It says a 20'' horizontal gap between the funnel and the paper. If I do this outside I'll try and set up "with" the wind, every little bit helps at this point. and yeah I'd be trying to get the letters higher up closer to the funnel. I'm trying to ask around to see if there's a local physics lab (there are a couple of community colleges and universities I've contacted) would be able/willing to assist with the construction and execution. And THANK YOU for your help!
     
  11. Jul 31, 2016 #10

    etudiant

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    The filings will travel down from the slot and hopefully towards your letter paper, so you want to give them as much opportunity to come to it as possible.
    That would suggest putting the letters down low or the funnel up higher, so a little magnetic nudge can help move the filings towards the paper.
     
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