Can you explain magnetism?

Discussion in 'Physics' started by sage.radachowsky, Jul 14, 2010.

  1. sage.radachowsky

    Thread Starter Member

    May 11, 2010
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    Hi... I have been all over Wikipedia and various other websites that attempt to explain the nature of magnetism, and I just get more and more confused.

    I have seen Maxwell's equations, and that explains "what" and "how much" but doesn't explain "how" or "why".

    I have heard mention of "virtual photons" and "lines of force" and all that stuff.

    Still, I don't feel that I really understand how a moving electron causes a magnetic field.

    I am ready to accept that some things can be observed but not explained, but I still am trying with this one.

    If anyone can help me out, maybe this forum will be the place where I finally understand.

    Some questions:

    1. If an electron is moving through space, and if you are looking at it going away from you, is there anything special about clockwise versus counterclockwise? I mean, is there anything actually going that direction or is it only a matter of convention for us humans, so we get our signs correct and predict the right outcomes? Same for the "right hand rule" and "right hand grasping rule" and those silly things. Do they really mean anything?

    2. If the answer of #1 is "yes" then is there only one kind of electron or two kinds? Like, is there a "left hand spinning" and "right hand spinning" electron in the universe? I know that quarks come in many flavors, but do electrons?

    3. If electrons are moving in a copper wire, then they are not really moving in a straight line -- they are swinging all around the atoms of copper, but they are all *generally* moving in the same direction. Does the magnetic field really depend on this average motion?

    4. What "carries" magnetic field or is it more like gravity, where it's sort of bending space-time fabric? And how is a magnetic field related to electric charge in the axis of time? Because a magnetic field comes from a "changing" (moving) electric charge and vice versa.

    Maybe someone will have the key to make me understand this topic. I can use inductors but I don't understand what is *really* going on.

    Thanks for your wisdom, in advance.
     
  2. Markd77

    Senior Member

    Sep 7, 2009
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    It confuses me too. I think the answer to 3 is yes. The average speed of electrons in a wire is tiny (look up drift velocity). A snail could go faster than most drift velocities.
     
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  3. beenthere

    Retired Moderator

    Apr 20, 2004
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    I moved the thread over here for a better fit.

    I think that while "clockwise" (if you want to get mystical, it's "sunwise" and the opposite is "widdershins") is a convention, the right hand and left hand rules will let you predict current direction and reaction forces.

    Electrons have spins that can be distinguished. They all carry the same amount of charge.
     
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  4. sage.radachowsky

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    May 11, 2010
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    Thanks for the responses folks but I'm afraid nobody will see the thread anymore... I notice 1 people viewing "Physics" while 231 people viewing "General" forum... and that 1 is me!
    I didn't even know there was a Physics forum!
    Oh well, back to wikipedia again.
     
  5. bertus

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  6. sage.radachowsky

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    May 11, 2010
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  7. Wendy

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    Mar 24, 2008
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    Concerning Question #1, are you thinking electrons are the lines of force? They create them, but are not them. Electrons can be thought of as particles, as stable forms of matter (incomplete but real). They are tossed around inside a vacuum tube, for example. From here it gets murky (to me). Think of a ball or a gyroscope. They have spin, and conservation of mass means they do not change their direction of spin without an outside influence. Since an electron has mass, and is matter, it can have a spin too. I don't know if they have to spin, maybe they do. The spin determines the magnetic field around the electron. Grabbing one isn't really possible though, so you have to use other means. But we can measure it and change it. This spin is where permanent magnets come from. When the spins are all random the magnetic fields cancel, when more spin one direction than the other you get a permanent magnet.

    Photons interact with electrons. Electrons "store" photons (not quite, but close). They absorb photons and jump out a level, or jump down a level and emit a photon. This is fundamental to lasers and how they work.

    Magnetism and the electric force are both fundamental forces. Together they make electromagnetism.

    The relationship between magnetism and electricity, which you already know. Moving electrons generate magnetism, moving magnetism generates electricity. Why this is so I don't know other than accepting it as part of nature.

    2. Is a ball spinning one direction different than a ball spinning a different direction? I don't think there is, but the magnitude of the energy they both have is different (Plus and minus), but the particles are the same.

    3. The relationship is firm, electrons and magnetic fields are related.

    4. I tend to think of magnetism as a form of space being stressed. I don't know how valid this is, but it is a fundamental force, and it takes a bunch of electrons working together to be noticeable, otherwise all the little fields cancel. They are always there though.

    Gravity and time are very related in much the same way, you can not change one without changing the other. Smarter people than I have been working this problem for a century, best guess there are particles called gravitons involved. Does this mean time is a field too? Who knows.

    This is my take, any or all could be wrong. You plays the game and takes your chances.
     
  8. studiot

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    Nov 9, 2007
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    It's likely that you will be confused if you have read widely about magnetism.

    I say this because there are many levels of complexity at which you can approach the subject.

    Modern thinking is that all magnetic effects are electric in origin. There is only one force. This view leads to some pretty fancy mathematical footwork in some cases.

    Once you start delving deeply into natural philosophy you have to stop asking questions like

    "What exactly is a .X.?" so we can't answer the question "What is an electron?"

    Because we simple don't know.

    The best we can offer is to say that we have a model which suggests that under certain conditions X behaves as though it has certain properties. So we can say that under normal circumstances electricity behaves like water in a pipe (but not completely) and that an electron behaves as if it had spin.

    But spin is a quantum number that depends upon the environment for meaning. The spin of an isolated electron, alone in its own universe, is meaningless.

    The interaction of a beam of electrons in vacuum (or air) interacts with magnetic fields in a certain way, quite differently from the interaction of magnetism with the electricity within a conductor which itself is quite different from the interaction of magnetism with electricity within a semiconductor.
     
  9. sage.radachowsky

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    May 11, 2010
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    Bill and Studiot, I appreciate your inputs.

    I agree with the sense that sometimes you must stop asking "what is X?" and get on with the practical matters of life. But sometimes I do wonder about things. I was reading a book called "The Whole Shebang" for example, and it blows my mind. For a while it feels amazing, to ponder the nature of existence, and then it gets to be too much for me, and I want to do some woodworking because chisels and wood are "real".

    But anyway, my primary question is about when an electron is traveling in a line... suppose it has a "spin" which is perhaps not actually a real spinning, but a quantum quality of some sort, that acts sort of like a physical spinning. That "spin" causes a magnetic moment, as I understand it. That magnetic moment will have a polarity based on what spin the electron has...?

    Suppose you have a billiards ball moving in a line in space, and spinning. It could be spinning on any axis in relation to the direction of linear movement. Or the axis of spin could be itself spinning in relation to the axis of linear movement.

    But in the case of an electron, is the "spin" aligned with the direction of movement by some cause?

    My gosh, I get so confused with this stuff... perhaps it's time to go back to programming a microcontroller, which is simpler.
     
  10. Wendy

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    Mar 24, 2008
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    Direction of spin determines where N and S is, a real measurable quantity.

    Normally alignments are random, and cancel. It is when the average alignment of N/S poles agree you get a magnetic field, the actual quantity of alignments is very small. It is a statistical average sort of thing.

    If I really wanted to muddy the waters I would have mentioned monopoles, but just forget I said anything. :D (evil laugh)
     
  11. studiot

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    I am not saying stop asking "what is X..?" because I advocate some other activity.

    I am saying it because the only perfect model for X is well, X.

    The only thing (model) which behaves exactly as an electron is all respects is an electron.

    We have models (mathematical or otherwise) that copy some of this behaviour.
    So an electron is not anything but itself.

    One of the models suggests that an electron in certain environments can be characterised by certain numbers we call quantum numbers. These numbers are solutions to the equations that govern quantum mechanics. These equations are made up in part from the mass and charge on the electron and part from the environment (potential fields) that electron finds itself interacting with.

    I recommend strongly against trying to explain magnetism in terms of electrons viewed as point charges with mass (or point masses with charge). This will lead you to the fancy mathematical sleights of hand I mentioned and you will be forced to conclude that in certain circumstances electrons posess negative mass. This is known as the Hall effect.

    The simplest (and earliest) explanation is simply to observe there is an effect, quantifiable in terms of a proposed magnetic field, and develop and use magnetic circuit theory.

    To explain both the link between magnetism and electricity and how magnetism arises in some materials Rowland Ring theory can be used.
     
  12. masked

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    Jul 1, 2010
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    Wow - as I'm sure you already know, there's a lot to these questions.
    But to scratch the surface, as far as I understand it:

    To #1: Yes. The special thing about the direction of rotation is that these directions are what we have always observed. From what we can tell, there IS actually something going in that direction. (I'm calling a "force" a "thing" for the purposes of this paragraph). The electromagnetic force/wave propagates out from the point of charge as a transverse oscillating wave which is rotating in the observed direction. The quantum perspective says that the wave can propagate at light speed. The practical result of this directional observation is that I can know which way to wind my coils.

    To #2: Classically, no. All electrons are considered fundamentally the same although they may have different states (different behaviors). If you're a philosophy student then things get fuzzier because a blue cat may be a fundamentally different entity than a grey cat depeding on how you define properties and attributes.

    To #3: Yes.

    #4 (part a) becomes hard to discuss without a well defined frame of reference - As do the finer points of question #1. Being one of the 4 "fundamental forces", we generally accept it as an observed fact but all else is speculative. If you study the history of theories on "the ether" you'll get a good understanding of the major points of view on this. But in the end the questions degrade into "Wat medium does *anything* exist in?" "What is the nature of matter/energy?" "What is the nature of existence?", etc.
    (part b) Magnetic and electric fields are actually one and the same (although we treat them as separate vectors in many cases). So one does not "interact with the other" in the axis of time... the *single* field "changes along the axis of time" the same as anything else; because we make our observations within the framework of time, and call the differences in observation "change" the two are apparently tied together.

    Maybe each question should be a separate thread :) I was trying to be very brief but failed.

    I have seen one explanation for the specific rotational direction of observed forces. There's a lot to it, but the gist is that it involves a multidimensional universe where the successive dimensions are functionally packed into concentric spheres like layers of an onion. A given amount of energy can "punch through" or be passed between dimensions in discrete quantities given a specific amount of energy at a specific time frame. When energy "punches through" to a progressively "higher" or "lower" dimension (similar to an electron moving between shells) we observe energy emanating up from lower-state dimensions as clockwise forces and down from higher-state dimensions as counter-clockwise.

    Also - don't get too hung up on the quantum "spin" being like a ball rotating in a specific direction. We basically just needed a way for two electrons to coexist in the same place when moving between s,p, and d shells, so we said "they just do" and called it "quantum spin". Later on, quantifying this difference became very useful in our equations and we've kept the name "spin". It's safer to think of it as "some different state".

    Hope that didn't murk things up worse.
    -masked
     
    Last edited: Jul 28, 2010
  13. Potato Pudding

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    Jun 11, 2010
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    I would be fairly certain that the Monopole is impossible. It is like saying you can separate the front of a sheet of paper from the back.

    Even if you split the sheet of paper what you have left still has a front and back.
    Magnetic north and south poles are differential qualities related to spin dynamics. To create a monopole you would need a partial spin - something that has one value of spin in one view and no spin in another view.

    At least that is what I think will make a monopole impossible.

    Magnetism very likely has to do with higher dimensional properties and their crossing influence on our perceived space time.

    Don't try to completely understand the how and why of magnetism unless you are involved in unification theory and other cosmological questions because it is part of the unsolved questions.

    It is amazing to realize that something so fundamental is still a mystery but that is science for you. Making a cellphone is easy compared to explaining some of the magnetism details in the signals that the phone uses.

    Arrangements of matter and flows of energy can create magnetic fields and magnetic fields can affect the flows of energy and arrangements of matter.

    It is so it is.
     
  14. Wendy

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    Mar 24, 2008
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    Actually the effect has possibly been observed, and the math demands it from what I've read. Go back through the physics forum, you will find a thread by Dave announcing the possible discovery of one.

    Getting a monopole is merely difficult, not impossible. They used to say nothing could go faster than the speed of light, now we have quantum entanglement. This is definitely a quantum effect.

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

    It's funny, we keep hearing the same thing about superconductors (nothing can be zero ohms) from various members, yet those are well documented.
     
    Last edited: Jul 31, 2010
  15. Potato Pudding

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    Jun 11, 2010
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    I was offering an unqualified opinion about Monopoles. Shame on me.
     
  16. Wendy

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    Science is one of my hobbies and fascinations. I'm not sure what we would use them for, but I'm sure they'd be useful for something.

    They are also a pretty common subject for this forum, because of their uniqueness. I suspect if you google them you will get huge numbers of hits, a lot of it bogus.

    Science isn't interesting to a lot of folks, or they don't bother researching more than the superficial. Hence the ban on HHO here at this site. We used to discuss it in depth, but some folks take it to the status of religion.
     
  17. steveb

    Senior Member

    Jul 3, 2008
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    There are ways to get some physical understanding about your questions. I'm not going to try and answer all the questions here because there is just too much to go through in a single response. Please see the attached article which provides an explanation of how to view magnetic effects as a manifestation of electric effects and Lorentz length contraction.

    These are difficult things to think about, but if you really want to explore this more, you can consult the book by Purcell, referenced in the above article. The book is fairly advanced and is targeted for senior level undergrad courses or first year graduate classes. Unfortunately, the book is a little expensive, but it's a classic and very unique.

    Even after years of studying electromagnetics, I often think about similar questions that you've asked here. Just recently, I've been working on a derivation of Biot Savart's Law from Coulomb's law, using the ideas in the above article.

    Probably the most useful concept you can come to terms with is the idea that electric and magnetic fields are components of the electromagnetic field tensor. The idea is that these field components must transform (obeying Einstein relativity transformations) in a way so that Maxwell's equations are valid in all frames of reference. So the odd thing is that even though one can think of magnetic effects as being electric in origin, one can never really understand all phenomenon from solely the electric field standpoint, except in special problems that have been arranged to provide a frame of reference that has only electric fields and another frame with only magnetic fields, but these are special cases and that idea does not apply in general. However, by looking at these special cases, you get insight into why electricity and magnetism are two sides of the same coin.
     
    Last edited: Aug 1, 2010
  18. steveb

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    Jul 3, 2008
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    Yes, I remember that thread as well, and it is definitely an interesting effect. One important point we should make is that this effect is a quantum effect in a material that produces a psuedo-magnetic-monopole and not a real one. Basically, south-pole and north-pole pairs (that can exist separately in space) are shown to exist, very similar to the way hole/electron pairs exist in a semiconductor.

    It's important to point this out because the discovery of real magnetic monopoles would be a major discovery that would have a huge impact on theoretical physics. We'll know when that happens because it will likely make the front page of Time Magazine and will surely earn a Nobel Prize to the discoverers.
     
    Last edited: Aug 1, 2010
  19. Wendy

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    Mar 24, 2008
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    We keep getting signals, but they aren't very repeatable. Either they are rarer than thought, we are looking in the wrong place, they are much different than predicted, or they don't exist. I tend to believe the first 3 options.

    Many cases discoveries are obvious after the fact. The evidence is in the data but it was missed. The 3rd option would cover that scenario.

    I notice that the Nobel prize can take many years or decades for anything to be awarded. Even when they are recognized it can be well over 10-20 years after the fact for a Nobel prize to be awarded. I'm not going to hold my breath.

    There is an old saying (I don't remember who made it, Arther C. Clark?) that for science to advance the old men have to die for new theories to have a chance.
     
  20. steveb

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    We all have our biases an desires, but science is all about establishing repeatable experimental evidence. There are theoretical grounds that make monopoles seem likely, and there are other theoretical grounds that make them seem unlikely. So, it turns out that a discovery of monopoles can have a major impact on theoretical physics. My old EM professor felt as you do, and I did as well until recently. The thing that changed my mind (and my mind is irrelevant of course) is the book "Foundations of Classical Electrodynamics: charge flux and metric". This book establishes the foundations of classical electrodynamics even in the context of general relativity. A key feature of this is (and I quote) "magnetic monopoles are alien to the structure of the axiomatics we are using. In our axiomatic framework, a clear asymmetry is built in between electricity and magnetism in a sense of Oersted and Ampere wherein magnetic effects are created by moving charges. This asymmetry is characteristic for and intrinsic to Maxwell's theory. Therefore the conservation of magnetic flux and not that of magnetic charge is postulated as the third axiom."

    What this means is that not only is there no experimental evidence for magnetic monopoles, but the very structure and foundation of Maxwell's equations do not imply that monopoles are a needed missing piece that establishes a desired symmetry in the theory, as some people say. This ties in perfectly with my previous post about how magnetic effects can be viewed as the effects of charge (electric force) combined with Lorentz length contraction (i.e. the theory of relativity).

    That said, there are other physics theories (which I don't understand anywhere near as well as electromagnetics) that predict magnetic monopoles as consistent with the theory. But, as pointed out in the above book, "Not long ago, Y.D. He, Phys. Rev. Lett. 79 (1997) p. 3134 and B. Abbott et. all, Phys. Rev. Lett. 81 (1998) p. 524 and G.R. Kalbfleisch et. al., Phys. Rev. Lett. 85 (2000) p. 5292 determined experimentally new improved limits for the nonexistence of Abelian or Dirac magnetic monopoles. This ever increasing accuracy in the exclusion of magnetic monopoles speaks in favor of the axiomatic approach ... ". Still, this is just another way of making your point Bill that maybe "they are much different than predicted".

    I agree. This is why I mentioned the Time Magazine cover article. First we will see the story there ( or in a similar place) then it will take years to verify the discovery. Once confirmed, the discovery is absolutely certain to result (eventually) in a Nobel Prize.

    Yes, I've heard that too. Like many sayings, it is an extreme exaggeration stated to make a good point. In this case, the point is that people are often reluctant to change. But, really science advances too fast now to wait for people to die. A clear discovery of monopoles will have some rapid consequences.
     
    Last edited: Aug 1, 2010
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