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Glass Lens affects Magnetic Fields?

  1. Sep 30, 2009 #1
    Hello all,

    doing some reasoning and subsequent Gadenkin experiments, followed by a Non-scientific experiment results in some interesting changes in magnetic fields using glass lenses. Here it is, and please help me to explain this phenomenon, as I can find no mention of it anywhere.

    Two bar magnets of equal size and strength.

    One magnet has a convex glass lens adhered to each pole end.

    One has no lenses.

    Each magnet is suspended above a wood table (no metal anywhere near) using plastic shims.

    A white card stock paper is laid over each magnet

    Fine iron filings are sprinkled (as evenly as possible) from a shaker over the paper

    The magnet with the lenses exhibits sharp deformation of fields, creating a well defined pattern significantly different from the norm, bending the field upward and to the sides of the lens and essentially removing the fields from the usual outward direction.

    The magnet without the lenses, exhibits the familiar pattern usually associated with a bar magnet.

    Remove the lenses from one magnet and apply to the other, and the same patterns are observed for the newly lensed magnet.

    The effect extends greatly into the bar itself, up to a third of its length using the lenses I have. The effect changes when the lenses are changed and using a different magnitude lens.

    I will be trying a concave shaped lens later, but wanted to post this for possible input on this result.

    This experiment idea comes from the fact that light is rotated and bends when passing through a magnetized glass plate (Faraday effect and other variations) but it seemed to me that if light bends through a lens, then magnetic fields should also be affected by the structure of the glass. However, I find no reference to this effect using the normal terms in Google or other search strings.

    Please respond with suggestions and or explanations.

    .. Since posting I have subsequently tried a variety of magnet combinations, and have successfully "killed" the magnetic field around a small horseshoe magnet. In other words, no filings will stick to the magnet at all in any spot on the magnet. By placing the lens in between the two poles the effect is the near extinction of the magnetic field. Remove the lens, and the field returns to normal.

    Any thoughts on this phenomenon will be greatly appreciated, as this seems unusual. It seems to me that someone at some time must have tried this out before, although who else would think to stick an optical lens on the end of a magnet.
    Last edited: Sep 30, 2009
  2. jcsd
  3. Oct 1, 2009 #2
    I'm probably gonna be outed as a fool for saying this but I don't think that's possible. At least what I think I read...

    Anyone know how this could work?

    Would the fact that glass is a good dielectric do anything here?
  4. Oct 1, 2009 #3

    Andy Resnick

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    The results (as stated) fly in the face of everything I know about electromagnetism, assuming the glass is typical glass, and there is no metal frame around the lens.

    How big are the lenses? That is, are they larger than the endfaces of the magnets?
  5. Oct 1, 2009 #4
    I know, it is a bit strange, but here it is. This could be a possible diamagnetic effect, but with two slightly different focal lengths of lenses, I get two slightly different patterns. The small horseshoe magnet is very weak, and that probably has something to do with what happened with it, and as I turned it so the side was facing up, I did see the lines in the pattern, but they disappeared from the top and bottom.

    http://i679.photobucket.com/albums/vv152/GraviMag/MagneticFieldexperiments.jpg [Broken]

    I have tried plate glass, a chunk of lead pounded to the same shape as the lens, cardboard, gaff tape, ceramic, etc. No other material shows this type of pattern. I will be securing more lenses from a hobby store today and I will try them. I'll get plastic, glass, and even some glass that is not necessarily a lens but distorts light. If anyone else would like to try some things, please post the results, as this is baffling me when I refer to what I've been taught about magnetics.

    Last edited by a moderator: May 4, 2017
  6. Oct 1, 2009 #5
    Those pictures all seem pretty standard, I don't see any effect that I haven't seen in other pictures / elementary classroom experiments before.


    The only evidence it that the pattern looks different in the pictures that say there is a lens on it. If the paper was not flush at the same height exactly for each sprinkling it could cause those patters to happen... Like if the paper was resting on the lens or something.

    But who knows, I honestly want to go out and try this for myself now.
  7. Oct 1, 2009 #6
    yes, the pattern by themselves, still look similar to other by themselves, but when compared side by side, there is a definite difference as you can see in the image. I've tried to be as careful as possible to ensure that the top of the lens is not supporting the paper, even setting the lens just slightly lower, but the same pattern emerges. Like I said, when I put the lead in place of lens, the pattern looks like the magnet without lenses. Everything else I've tried also exhibits the non lensed pattern, so there must be something to the glass or shape of the glass.

    Granted, this is not in a lab and I admit that a more stable environment is needed to test this, as well as new fresh magnets, different lenses, different materials, etc. But as the one who is looking at this strange effect, I am compelled to go forward and try everything that I can to cause this effect to fail with the lenses. Perhaps these lenses have a coating I am not aware of?

  8. Oct 1, 2009 #7
    Try it with a plastic lens and a square piece of glass?
  9. Oct 1, 2009 #8


    Staff: Mentor

    Sorry Gravitron, I don't see the difference you are talking about. As far as I can tell the field lines are in the same direction with and without the glass.
  10. Oct 2, 2009 #9
    Well if you ignore the talk about field lines and just compare the overall look of the pattern the fileings make.
    I don't know if anybody else concurs but both the magnets without lenses look similar as do both with lenses (they look like pairs).
    However if you observe one with a lense and one without they do not look similar.
  11. Oct 2, 2009 #10


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    I dunno, they all look pretty similar to me... except that the patterns with the lenses have a few more iron filings on top of the magnet itself (at one end). Maybe the glass blurs the effect of the sharp edges of the magnet a bit.
  12. Oct 2, 2009 #11


    Staff: Mentor

    But the field lines are all that the filings indicate. The regional clumping and other things that contribute to the "overall look" don't mean anything about the field, only the direction of each filing. I'm sorry to disappoint, but in all of the images the filings are in a very typical magnetic dipole pattern. I see no evidence of focusing.
  13. Oct 3, 2009 #12
    Yes but can you distiguish between the magnets with the lens attached and the ones without.
    The ones with have a distinctive prickley pear look with the fileings distributed across the whole of the end of the magnets.
    The magnets with no lenses attached, lack this distribution.
    If you were to do a blind test it would be possible to recognise the magnets with lenses attached and the ones without.
  14. Oct 4, 2009 #13


    Staff: Mentor

    Sure, but the "prickley pear look" does not indicate anything about the field. What it indicates is something about the initial state of the filings themselves and the setup. From a conceptual stand point, it is like you are making measurements with a ruler and then claiming you have measured a change in mass.
  15. Oct 4, 2009 #14
    It could indicate something about about the setup then again it could be the field.
    Certain variables about the setup would have to be eliminated to be sure.
    Blackening the lenses before attaching them to the magnets to see if the "prickley pear look" persists.
    Also different material of similar shape to the lenses could be substituted to eliminate the initial state of the setup.
    If the field remains the same or very similar after these substitutions then it is the setup.
    However if the feild changes and the "prickley pear look" is no longer present then the lenses are somehowe effecting the field.
  16. Oct 4, 2009 #15
    What is the general shape of the iron filings?I am guessing that they are sort of rod shaped having one linear dimension longer than the others.After some staring at the pictures I think I can see the "prickly pear look" and it seems to me that the iron filing prickles are more upright.I think this is to be expected since each filing becomes magnetised and points in the direction of the field the resultant force having a greater vertical component as the poles are approached..This leads me to suspect that the card used was not laid at the same height above both magnets.A small difference in height can make a big difference to the pattern observed.Remember that the field is three dimensional and the detected field becomes more horizontal as the card gets closer to the magnet.Gravitron,if you haven't already done so perhaps you could repeat your experiment using some sort of spacers to ensure that the card height is the same in both cases.
  17. Oct 4, 2009 #16


    Staff: Mentor

    Like what? What exactly about the field is "prickly pear"-ness measuring in your opinion?
  18. Oct 4, 2009 #17
    It took me some time to see it but it looks like the filings close to the poles are standing more upright ie pointing downwards towards the poles.As you move away from the poles and towards the centre the filings seem to become more horizontal.These are results I would expect but my eyes could be decieving me.
  19. Oct 4, 2009 #18


    Staff: Mentor

    Sure, the field is 3 dimensional, and the direction of the filings does indicate the direction of the field at their location as I mentioned earlier. Do you think the filings indicate anything else about the field?
  20. Oct 4, 2009 #19
    There are so many variables and a lack of clarity but from what I can make out so far I don't see any focussing or anything else unexpected.
    Last edited: Oct 4, 2009
  21. Oct 4, 2009 #20


    Staff: Mentor

    I agree.
  22. Oct 4, 2009 #21
    Well to be honest I am not quite sure.
    Untill all the variables are accounted for or eliminated it could be insignificant in as much as someone else mentioned that the distance from the magnet to the paper is inconsistent.
    Then again it is noted that the experimenter has tried to keep these distances the same and that different lenses in his opinion produce different effects.
  23. Dec 31, 2009 #22
    After many many experiment with different lenses of different substances, I can report the following.
    1) out of all the lenses I've tried, the original lenses as posted were the only ones that caused this slight deflection of the pattern of iron fillings. All others were, as far as I could see, were identical to the pattern that was formed with just the magnet.

    2) I could not find any information as to what specifically the lenses were made of, only that they were mass produced for use in LCD projector construction.

    3) I used a diamond band saw to cut one of the lenses in half and as I polished the cut edge, noticed that there was some degradation of the glass in one area. After looking at this area in a microscope, i noticed that there was a small "pocket" in the glass. I assumed this was a bubble. After careful observation, I noticed many more of these pockets. I believe that these are bubbles in the glass, not noticeable to the naked eye. If these bubbles were filled with a gas, or even a vacuum then I would hypothesize that the magnetic field found it easier to go around these bubbles, thereby creating a slightly different pattern of the field. Is this possible?

  24. Dec 31, 2009 #23
    Well, here's my thoughts for what there worth:

    First, it IS possible for an optical lens to have ferromagnetic contamination that is not noticed, or even concerned with, in it's use in BASIC optical applications, such as an LCD projector.
    Even a standard piece of writing paper has trace amounts of iron, gold, plutonium, etc...

    It would not surprise me at all that some manufactured lens' might have trace amounts of iron. Whether the amount and distribution is enough to cause an un-aided eye view of magnetic field distortion is another matter.

    On the issue of "bubbles" there are a couple problems here.
    Those would be very poorly manufactured len's, yet might also account for the propensity for manufacturing contamination of ferromagnetic atoms.

    Even still, if you can see these bubbles with a standard microscope, bear in mind that the size of each bubble is ENORMOUS with respect to photon passing through it. And if not it still doesn't matter.
    That means that those bubbles act in themselves as visible light len's.

    I would imagine that this would cause an unacceptable distortion of the LCD projected image. Thus, I somewhat doubt that you are correctly assessing that there are numerous bubbles, as that lens would be rejected.

    Importantly, however, without ferromagnetic contamination of some sort, a "pure" glass lens with or without bubbles WILL NOT distort a magnetic field, to my understanding, that is.
    Last edited: Dec 31, 2009
  25. Jan 2, 2010 #24


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    I don't think anyone ever mentioned it specifically before but your original reasoning is faulty. Lenses affect light by their affects on the electric field of the electromagnetic wave. They are designed to have permittivities that differ from the surrounding medium. The resulting boundary conditions only directly work on electric fields, magnetic fields are not influenced by permeabilities except for the fact that in an electromagnetic wave the two fields are now bound together. You should have no expectation that a lens affects a magnetic field unless, as pallidin mentioned, it contains extraneous contaminants that have non-vacuum permeabilities.
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