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For a science fair project I am building a coilgun and so far it has been pretty easy but now I have run into an issue. I have 2 layers of coil wrapped around a straw and when I attach power to the coil and try and put something magnetic inside it it doesn't attract it at all. If you need pictures I would be glad to attach some.

EDIT Here are some images enter image description here

enter image description here

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closed as off-topic by Yashas, Kyle Kanos, honeste_vivere, valerio, Qmechanic Jul 22 '17 at 16:28

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    $\begingroup$ Is your wire insulated? It should be. $\endgroup$ – mattfitzgerald Oct 13 '16 at 0:06
  • $\begingroup$ @mattfitzgerald With 2 layers of enamel. amazon.com/gp/product/B00E1P4VD2/… $\endgroup$ – xFlarp Oct 13 '16 at 0:12
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    $\begingroup$ If you have a compass handy, that would be a better indicator of a magnetic field begin generated when you put one of the ends of the coil near it. $\endgroup$ – Mark H Oct 13 '16 at 0:49
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    $\begingroup$ It might be that you wrapped the top layer in the opposite direction, that cancels the magnetic field of the first layer. $\endgroup$ – ahemmetter Oct 13 '16 at 7:30
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    $\begingroup$ I'm voting to close this question as off-topic because the apparatus is theoretically correct but is not working because of some issue. It is not possible to guess what the problem could be because it could be anything (from a failed battery to a current leak in the coil and what not). $\endgroup$ – Yashas Jul 21 '17 at 4:30
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If it doesn't get warm there's no current flowing. You didn't show the rest of your setup, but are the ends of the wire stripped? Is there any possibility of a break in the wire somewhere?

If it does get warm the only other possibility is that you somehow reversed the wire when you started the second layer, and they're cancelling out magnetically.

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  • $\begingroup$ The ends of the wire are stripped and no I don't think it is a break I think your second idea could be much more possible but let me see if it gets warm. $\endgroup$ – xFlarp Oct 13 '16 at 0:43
  • $\begingroup$ Ok it does get warm but not as much as the battery. Also when I connect the wires to the battery small sparks come off I am not sure if that is anything but I thought I would put it out there. $\endgroup$ – xFlarp Oct 13 '16 at 0:45
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    $\begingroup$ Well current is definitely flowing in the wire, so yes, it must be that the two coil wraps must be fighting each other. $\endgroup$ – D. Ennis Oct 13 '16 at 2:41
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You are sure that the object that you put inside the coil to test for attraction is really magnetic (i.e., it sticks to a refrigerator) and is not simply a non-magnetic metal?

It would be helpful if you gave some information on the dimensions of your coil and also the gauge (diameter) of your wire as well as the amount of current you are running through the wire.

Even without knowing this information, however, I think that the length of the coil is not optimal to generate a large magnetic field at the ends of the coil where you put your magnetic test object at in order to test for magnetic attraction. Look at it this way: The windings of the coil at the right end of the coil contribute a significant magnetic field to regions near the right end of the coil, but those windings at the far left end of the coil are rather far away and don't contribute much at all to the magnetic field near the right end of the coil. So a lot of the windings of the coil really aren't contributing much in exerting any significant magnetic force on a test object placed near the right end of the coil.

I would change the aspect ratio of the coil so that the length-to-diameter ratio of it is not so large, and also increase the number of wire layers to something quite a bit more than just two. Do a Google image search for doorbell solenoids and you'll see that they have significantly smaller length-to-diameter aspect ratios and also many more wire layers than the electromagnet you made.

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Given that you said the battery gets hotter than the wire and that sparks happen when you disconnect it, you definitely have a good amount of current flowing. The sparks are caused by the inductance of the coil, so you know you have some magnetism being generated.

Your problem is that you simpky have nowhere near enough turns. You will likely need many many more than that to make an appreciable magnetic field. You may need at least 10x more layers than that to make a coil gun.

Another problem is that field strength is inversely proportional to the core length. If you wrapped the same amount of wire over a shorter section of straw, it would make a stronger magnetic field. Lengthening the magnet will not make it stronger, because the proportional increase in turns is exactly offset by the proportional increase in length, leaving the field exactly as strong as before.

In summary, your electromagnet is weak because there isn't nearly enough electro.

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