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Changing polarization of a magnet for a project of mine

  1. Nov 7, 2006 #1
    Hi,

    I'm considering working on something (vague, I know), but the whole thing hinges on whether or not it's possible to change the polarization of a magnet, and how. The basic premise is that I need two magnets which are attracting each other (so one positive and one negative charge), but I need to be able to touch something to or change something connected to one so that it switches polarization and the two now repel. The idea is to have one held still and the other push back a spring by the force of repelling, and then when you let go of whatever is changing the magnet's charge the one with the spring (through the attraction and the force of the spring) slams back into the one held still. It seems like this is possible (I remember something about changing the flow of electrons from high school), but I'm majoring in political science so it's a little beyond me :) It seems like I would need a battery or something and a wire touching the magnet...? I don't know.

    Also, how would I go about extending the range of the magnetic force? I need this spring (which is fairly strong) pushed back about five or six inches, so I think I'd need more strength. Would magnets along the sides do it? Or if I could fine a magnetic tube to put the other magnets in? Also, does anyone know where I could order these magnets? I searched froogle but came up largely empty, I mainly got big magnets when I'm looking for (ideally) smaller cylindrical ones, and possibly that tube.

    Thanks in advance, I appreciate any help
     
    Last edited: Nov 7, 2006
  2. jcsd
  3. Nov 7, 2006 #2

    Danger

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    Welcome to PF, alasz11. What you need is one electromagnet (the switchable one) and one permanent magnet. You could use two electromagnets and leave one on constant polarity, but that would be a waste of electricity. To reverse the polarity, you just switch the positive and negative leads from your power supply (DC, or course).
    As for extending/amplifying the field, I'll leave that for someone who knows more about it.
     
  4. Nov 7, 2006 #3
    Thanks! Now, how exactly would that work in practice? I've drawn up kind of an example (in the attachment). If I were to run wires from each end of the battery to the electromagnet, would that change the charge? So that every time I want to change the charge (to make the permanent magnet be repelled) I would just touch the wires to the electromagnet? Sorry if I'm way off, like I said my understanding of this is from basic high school science classes.

    Also, can regular metal be turned into a magnet? I was thinking it might be easy if the entire tube around both magnets was magnetic and changed with the electromagnet, that might cause the field to extend further down, right?

    Err... wait, upon further researching, an electromagnet is just metal (like iron) attached to a D battery, right? So for the electromagnet I would mainly need a piece of iron or something that is turned "on" (repelling the permanent magnet back) and "off" (stopping the repulsion, allowing the metal to just be regular ol' metal with no charge, so the spring can slam the permanent magnet down the tube into the electromagnet) by touching the wires to it? If that's correct, how strong can the attraction or repulsion be? I think I'm going to need it to be fairly powerful so it can push back a strong spring, what would I have to affect to increase the repulsion?
     

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    Last edited: Nov 7, 2006
  5. Nov 7, 2006 #4

    berkeman

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    To get the best bang for the buck (strongest mechanical forces per electrical power input), look at using an electromechanical solenoid arrangement:

    http://en.wikipedia.org/wiki/Solenoid

    These work by forming a magnetic field in a coil (the solenoid), which pulls a metal rod into to the coil. If you need push/pull action, you use two coils to pull a rod in two different directions (not at the same time).
     
  6. Nov 7, 2006 #5
    Interesting that that article mentions paintball markers, my project is for a similar application. I'm trying to come up with a better way to pull the spring in airsoft guns, the current way most are done is just using a motor to turn gears to pull the spring back, but that takes a large battery and all the moving parts interlocking gives reliablity problems.

    Anyway, how exactly would that fit in? I'm a little confused, would you hook the magnets up to the solenoid? Or is the solenoid itself the magnet?
     
  7. Nov 7, 2006 #6

    LURCH

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    Speaking of wasting electricity, if you have a spring, you don't really need the electromagnet to be reversable. Simply turning it "off" will allow the spring to force the permanant magnet up against it. Even i fyou need the two to be held magnetically for some reason, switching off the electromagnet will turn it into an ordinary piece of metal, to which the permanent magnet will be drawn.
     
  8. Nov 7, 2006 #7
    Yes, I was reaching that conclusion in my mind but I'm glad you confirmed it :)

    Does anyone know where you I can get the materials I'd need for this? I've done some Froogle searching but nothing really came up. I basically need a tube (probably at least an inch inner diameter, I've found ones that big but they only come in 10'-20' length, and I only really need 6"-1', I'd rather not pay $80 for a huge one) and metal cylinder which can be put in one end (this would be the electromagnet). Like I said earlier I think it would be good to have the tube be an electromagnet as well, wouldn't their combined forces be pretty strong forcing the permanent magnet out the open end? And of course a cylindrical permanent magnet that can fit in the tube. I imagine I can come up with the wires, and the spring I can just order from an airsoft supply shop.

    thanks
     
  9. Nov 7, 2006 #8

    Danger

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    If your tube needs to be steel, I'd suggest checking with an automotive supplier. I think that some exhaust pipes for smaller rice-rockets or motorcycles are about the size that you're looking for. Otherwise, go to a plumbing shop for some ABS, PVC or whatever.
     
  10. Nov 7, 2006 #9
    I don't think it needs to be steel specifically, can't any kind of metal become and electromagnet (like copper or iron)? Or is steel going to give the best magnetic force?

    Edit: Well, regardless, here's some steel tubing at various lengths and wall thicknesses: http://www.aircraftspruce.com/catalog/mepages/4130tubing_un1.php

    is wall thickness going to make a difference in strength if I turned it into an electromagnet?
     
    Last edited: Nov 7, 2006
  11. Nov 7, 2006 #10

    Danger

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    I misunderstood; I thought that Berkeman's post made it clear that you should use a solid rod for your plunger. The tube would be just to keep things aligned. And no, not just any metal can become a magnet. It has to be either iron or some exotic material such as samarium-cobalt. Alumininum, brass, lead etc. are specifically not magnetizeable.
     
  12. Nov 7, 2006 #11

    berkeman

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  13. Nov 7, 2006 #12
    ah, I vaguely remember the term ferrous, it has to do with outer electrons, right?

    Is there some harm in this? Would having the tube be made or iron and part of the electromagnet work against me? It seems like it would just be that much more repulsion all the way up and down it.

    Also, I read some stainless steels are magnetic (martensic is the word?) and some aren't (autensic). How can you tell if it is or isn't (like in that link I posted above?)
     
    Last edited: Nov 7, 2006
  14. Nov 7, 2006 #13

    berkeman

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    It has to do with the magnetic hysteresis of the material:

    http://en.wikipedia.org/wiki/Magnetic_hysteresis
     
  15. Nov 8, 2006 #14
    hmm.... alright, well, thanks guys, I think I've got the information I need to attempt this project. You've been very helpful, keep up the good work
     
  16. Nov 9, 2006 #15

    Danger

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    Good luck with it, pal. Keep us appraised of your progress. One thing about we PF'rs... once we get involved in something, we like to know how it turns out. :smile:
     
  17. Nov 13, 2006 #16
    No problem. I plan on working on it over Christmas vacation, we'll see how it goes then.
     
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