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Greg Bernhardt submitted a new blog post
Are Magnetic Field Lines Real?
Continue reading the Original Blog Post.
Are Magnetic Field Lines Real?
Continue reading the Original Blog Post.
That sounded like a challenge.Charles Link said:It may be worth mentioning that field lines drawn on a two dimensional piece of paper really don't work very well, because the line density for a source that radiates from a point need to fall off as inverse square, but on a 2-D piece of paper the line density falls off as 1/r. It is a much more accurate representation of actual field lines=they would be quite exact, if they were made out of wire on a 3-D model.
If we're both thinking about the same thread, the problem is something I kind of illustrated with the "bad choices of seed points". You could, indeed, represent the field lines around a moving wire as "moving along with the wire" by picking seed points for the field lines that moved along with the wire - but it's fairly obvious that you are drawing different field lines if you explicitly note that you need to move your seed points. If you used fixed seed points while the wire moves, the field lines just expand. The field lines change over time if the current is changing with time is, I think, the only safe statement of that kind that can be made.Sorcerer said:Thanks. @Ibix . There's been some real madness on the forums about this lately, and I think it stems from people taking the iron filling example to mean much more than it actually does.
I don't think so, although I'm open to correction. My understanding is that a path integral of some (not necessarily vector) field is its integral along a chosen path, while integral curves require the field to have a notion of direction and they let the field define the path. So if you walk through a rainstorm, how wet you get depends on the integral of the flow rate along the path you choose to walk - that's a path integral. But there's no sense of direction in a rainstorm, unless we go and look at the velocity field of the drops. Integral curves of that field would be the paths traced out by the drops as they fall.Sorcerer said:I do have one question. You said "[f]ield lines are the integral curves of a vector field." Can that sentence be translated into a path integral of some sort?
Or a stereogram. If you can kind of cross your eyes until the red wire loops overlap you get a kind of lame 3d effect.Ibix said:I think it may need some animation for you to be able to sort out the field lines clearly, but I don't have time right now to figure out how to do that.
Be sure to link to your Insight in that threadIbix said:If we're both thinking about the same thread, the problem is something I kind of illustrated with the "bad choices of seed points".
@Ibix I would say at least partly successful. It might work better for a cylindrical magnet than it does for a current loop. In any case, it does illustrate the point that the 3-D model is necessary to get the proper divergence of the flux lines, i.e. where density falls off as 1/r^2 from a point source, etc.Ibix said:That sounded like a challenge.
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It's a bit of a mess. I think it may need some animation for you to be able to sort out the field lines clearly, but I don't have time right now to figure out how to do that.
The thread I had in mind was this one: https://www.physicsforums.com/threads/moving-charge-in-a-magnetic-field-problem.958010/ Unfortunately it's locked and the OP got banned for something else the other day. But if someone with appropriate permissions thinks a link is appropriate and wants to add one, please go ahead.Greg Bernhardt said:Be sure to link to your Insight in that thread
It's surprisingly non-painful to create a YouTube video. It really needs to be watched in fullscreen mode because the field lines are too fine otherwise.Charles Link said:@Ibix I would say at least partly successful. It might work better for a cylindrical magnet than it does for a current loop. In any case, it does illustrate the point that the 3-D model is necessary to get the proper divergence of the flux lines, i.e. where density falls off as 1/r^2 from a point source, etc.
I agree this can only be a rule of thumb, because there are specific counter examples where the contours of magnetic field strength are different shapes from the magnetic field lines (a wire moving perpendicular to its length, for example). And there are cases where the field line density is completely a matter of choice (a stationary wire produces concentric circular field lines - the density is trivially related to the density of seed points).greypilgrim said:It's often said as a rule of thumb that the "line density" relates to the strength of the field.
You mean, can you see field lines being more spread out with the iron filings? No, because there is an infinite set of possible field lines. The density effect only works if you pick systematically placed seed points in a finite region where all field lines pass.greypilgrim said:Also, can this be seen with iron filings too? I've seen some images that suggest so, others that don't
Thanks!anorlunda said:Great Insight, and helpful to dispel misconceptions.
I don't think I know enough about solar plasma physics to follow your suggestion. I agree it would be a good subject, since I see your point about prominences potentially giving the impression of flowing along field lines. I just don't think I know enough to do it.anorlunda said:You can expand the article.
Ibix said:I don't think I know enough about solar plasma physics to follow your suggestion.
That's weird - it works if you "open link in new tab", but not if you just click on it. I tried to link to the page with all the file information instead of the image itself, but maybe Wiki doesn't like that? I'll investigate later.DrClaude said:Great Insight, but the Wikipedia link is broken
anorlunda said:I don't think you need to explain the plasma, but just mention that you're excluding plasma from the article. BTW, plasma lines cross each other, whereas the kinds of magnetic lines you wrote about can never cross; an important property.
I believe I've addressed both of these now - added a paragraph on solar flares and linked directly to the image on Wikipedia instead of its details page.DrClaude said:Great Insight, but the Wikipedia link is broken
Ibix said:Or a stereogram. If you can kind of cross your eyes until the red wire loops overlap you get a kind of lame 3d effect.
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Interesting. It works for me crossing my eyes inward, and that's the effect I was aiming for. It's possible I messed up creating it, of course! I think the video does the job better, so I shan't try to regenerate it.Swamp Thing said:At first I found it hard to see the 3D shape, even though I have a fair amount of practice viewing this kind of thing. But I realized that I was crossing my eyes inwards rather than outwards.
If you do it the other way around I think that should just result in mirroring the dimension going in/out.Ibix said:Interesting. It works for me crossing my eyes inward, and that's the effect I was aiming for. It's possible I messed up creating it, of course! I think the video does the job better, so I shan't try to regenerate it.
There may be a bit of subjectivity going on here depending on the post-processing in the brain. But when I cross my eyes inward, I am able to lock the two images together pretty easily -- but the fused image seems to have almost no depth.Orodruin said:If you do it the other way around I think that should just result in mirroring the dimension going in/out.
sweet springs said:OP states magnetic field line is not real. Even not real I wonder magnetic field or force line is indispensable in getting magnetic flux density B where flux of magnetic field line is taken.
As a beginner I am not aware of EM formula without the concept of fields. I will learn it. Thank you for your advise.bhobba said:That EM can be formulated without the concept of field shows convenience is often used to decide how to view something.
No, magnetic field lines are not actual physical lines. They are simply a visual representation of the direction and strength of a magnetic field.
Magnetic field lines are created by the movement of electrically charged particles, such as electrons, in a magnetic field.
No, we cannot see magnetic field lines with the naked eye. They are invisible, but can be visualized using tools such as iron filings or a compass.
Yes, magnetic field lines exist in a vacuum. They are not affected by the presence or absence of matter.
No, magnetic field lines can be curved or even circular depending on the configuration of the magnetic field. They can also change shape and direction depending on the presence of other magnetic fields.