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Solenoid Diagram

  1. Jul 24, 2016 #1
    1. The problem statement, all variables and given/known data

    upload_2016-7-24_19-2-20.png

    (http://imagemap-generator.dariodomi.de/uploads/160725_010743_e42ea59f2569dfbV.png [Broken])
    2. Relevant equations
    No equations or anything. Just need a visual concept understanding (11U Physics)

    3. The attempt at a solution
    The solutions say that all compasses should point east.... So is the force between the loops going east or west? Using the right hand rule and knowing it's a conventional current, I know which way it wraps around. But I'm really confused as to which way the inner force would point, and how to draw it. Is there a rule or concept I missed?

    Thanks.
     
    Last edited by a moderator: May 8, 2017
  2. jcsd
  3. Jul 24, 2016 #2

    phinds

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    I don't understand how you interpret that as being part of the question. Take the solenoids as existing far away from each other is how I read it.
     
  4. Jul 24, 2016 #3
    Sorry I might not have been clear. These are two separate diagrams. I need to find which way the force is going in between the loops shown, in order to see which direction the compasses will face.

    Each diagram has two compasses each. So

    Question 1) Which way will the two compasses point for a)

    Question 2) Which way will the two compasses point for b).

    Part a) and b) are not correlated and do not interact with each other.
     
  5. Jul 24, 2016 #4

    phinds

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    Do you mean the force INSIDE the loops of wire? I just can't understand your phrasing.
     
  6. Jul 24, 2016 #5
    Yes, the force inside the loop wire.
     
  7. Jul 24, 2016 #6

    phinds

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    Assuming the "solenoids" are thick-walled metal cylinders with a hole through the middle, what direction would a steel bead move if placed there and the current turned on?
     
  8. Jul 24, 2016 #7
    Towards west?
     
  9. Jul 24, 2016 #8

    phinds

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    Are you guessing or do you have a rationale for that answer? If you have one, post it. How do you expect us to help you if you don't show your work? If you are just asking us to give you the answer, you should go back and read the forum rules.
     
  10. Jul 24, 2016 #9

    A conventional current runs from the positive side to negative. When there is a coil that has a current running through it, it can create a strong magnetic force inside the loops of coil. This magnetic force runs from the positive side to the negative side, exits, and does it again, as far as my understanding. I know using the right hand rule which way the specific magnetic field is running AROUND the coil, but I don't understand how it works INSIDE the actual coil-created cylinder. Why does it create a force running parallel to the cylinder shape? Does that force eventually loop around as well, or does it stay constant?
     
  11. Jul 24, 2016 #10

    phinds

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    If the force is caused by the magnetic field would you expect it to go on it a straight line or follow the magnetic lines?
     
  12. Jul 24, 2016 #11
    I'd expect it to follow the magnetic lines, but in all diagrams I see, it goes straight and I do not understand why.
     
  13. Jul 24, 2016 #12
    I'm sorry if I'm a little hard to work with, I'm just trying to grasp the basic understanding of magnetic fields.
     
  14. Jul 24, 2016 #13

    Charles Link

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    I think I can offer an explanation that may help. I think you have already figured out that the magnetic field in the solenoid points from left to right. You assume the magnetic field from the solenoid is much stronger than the earth's magnetic field. One other item that needs to be explained is what a compass is. A compass has a magnetized needle in it that will align with whatever magnetic field is present. The "+" end of the needle (the pointing end=the north pole end) points north(without a solenoid) because the magnetic field of the earth goes from south to north. With a solenoid, you are artificially creating a magnetic field that points along the axis of the solenoid. The right hand rule allows you to determine the direction of the magnetic field through the solenoid. Your coursework is not advanced enough yet to do very much with actual magnetic forces, but you should be able to understand that a permanent magnet (magnetized iron) and a solenoid are quite similar in that they each have "+" and "-" poles at their endfaces and the field outside of them goes from the "+" and loops back to the "-". Inside the solenoid the magnetic field goes from the "-" end to the "+" end and the same is true for the magnetic field inside a permanent magnet (such as a compass needle or any other permanent magnet.) The other thing you need to know is that the +" poles repel each other (and the "-" end of the compass (needle) magnet gets attracted to the "+" end of the solenoid), so the needle magnet inside the compass will point away from the "+" end of the solenoid. Hopefully this was helpful.
     
    Last edited by a moderator: May 8, 2017
  15. Jul 24, 2016 #14
    Thank you so much. This clears up the concept well, you've explained it perfectly. I really appreciate it :)
     
  16. Jul 25, 2016 #15

    Charles Link

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    Just a follow-on comment: A very interesting homework problem. We did a number of experiments in college with solenoids, but we never used a compass needle to probe the magnetic field.
     
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