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  • what is a magnetic field?

    In 1950, when I was in the fourth grade, my science teacher told the class that "everything is a solid, a liquid, or a gas."

    I raised my hand and asked the teacher, "what's fire, or electricity?" I couldn't see how these were part of the teacher's triad. A smarter teacher could have explained that fire was indeed a gas (or perhaps a plasma), but Mr. Billodue was stumped and basically told me to shut up.

    Now I'm reading God's Debris, by Scott Adams (creator of Dilbert) http://images.ucomics.com/images/pdf...godsdebris.pdf, which asks the same question in a broader sense: what is a magnetic field?
    “Consider magnets,” the old man said. “If you hold two
    magnets near each other, they are attracted. Yet there is
    nothing material connecting them.”

    “Yes there is,” I corrected. “There’s a magnetic field.
    You can see it when you do that experiment with the metal
    shavings on a piece of paper. You hold a magnet under the
    paper and the shavings all organize along magnetic lines.
    That’s the magnetic field.”

    “So you have a word for it. It’s a ‘field,’ you say. But you
    can’t get a handful of this thing for which you have a name.
    You can’t fill a container with a magnetic field and take it with
    you. You can’t cut it in pieces. You can’t block its power.”

    “You can’t block it? I didn’t know that.”

    “You can alter a magnetic field by adding other magnetic
    material, but there is no non-magnetic material you
    can put between two magnets to block them. This ‘field’ of
    yours is strange stuff. We can see its effect, and we can
    invent a name for it, but it doesn’t exist in any physical
    form. How can something that doesn’t exist in physical
    form have influence over the things that do?”

    I still have no answer. Do you know what an electromagnetic field is?
    Last edited by aostling; 01-08-2009, 01:03 AM.
    Allan Ostling

  • #2
    Gravity is similarly mysterious. Figure out what it actually is and every one will remember your name forever.

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    • #3
      One of the most brilliant physicists of the last century, Richard Feynman, explained magnetic fields and its partner, electric fields in a theory known as Quantum Electrodynamics or QED. He gave a wonderful series of lectures to explain it to the common man at a University in New Zealand. They recorded it and it is available free on the internet. I can't think of anyone who could answer your question better than Feynman in these 4 lectures. They are also very entertaining. Here is the link:


      http://vega.org.uk/video/subseries/8

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      • #4
        Fields

        Originally posted by aostling
        I still have no answer. Do you know what an electromagnetic field is?
        A field that they grow electromagnets in?

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        • #5
          There are actually two valid answers.

          A magnetic field is a manifestation of the electromagnetic force mediated by the exchange of photons.

          The other answer is one that I used to give my customers when asked how a photocopier works. I would tell them that it worked by means of FM. When asked what FM is I would variously reply depending on circumstances "Freekin Magic" or a very similar but more emphatic version with the same meaning.
          Free software for calculating bolt circles and similar: Click Here

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          • #6
            A magnetic field is simply our way of describing the area over which the magnetic force acts.

            Magnetism or electro magnetism is one of the four fundamental forces of nature. The others are gravity and two that physicists refer to as the strong force and the weak force. The last two are only observed at very small distances like the size of atoms so we have no practical, day to day knowledge of them except that atoms do not fly apart and sub-atomic particles do interact with each other.

            All of these forces actually cause what has been referred to as "action at a distance". In other words, two objects will apply force to each other without actually touching. The idea of a "field" is our way of visualizing the way these forces act at various points (all points) around the objects that are interacting. In this sense, a field is not a physical object that can be touched or seen or gathered up in a bottle. It is an abstraction.

            As for exactly how these forces work, the latest thinking in the world of physics is that this is accomplished by exchanging small sub atomic particles between the objects. For gravity, these particles are called gravitons. For the electro-magnetic force they are called photons. All objects have some mass and therefore they will interact via the force of gravity. They do this by exchanging graviton particles. All objects that have electro-magnetic properties (again most do) interact by exchanging photons (aka electro-magnetic radiation). The strong force uses particles called gluons and the weak force uses ones called intermediate vector bosons. In the sense that the forces actually function via the exchange of particles, you may be tempted to say that these particles are the "fields". But I am not sure many scientists would speak of it in this manner. More correctly, the fields are simply an abstract description of the way these particles cause the objects to interact: a kind of mental graph of the forces.
            Paul A.

            Make it fit.
            You can't win and there is a penalty for trying!

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            • #7
              I still have no answer. Do you know what an electromagnetic field is?
              frustrated electricity with no where to go
              --
              Tom C
              ... nice weather eh?

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              • #8
                Can't answer your question, but if I had a nickel for every time the teacher jumped on me for an 'inappropriate' question", (similar to the electricity question) I'd be a rich man right now.

                Years ago I had a teacher who jumped all over my sh*t because I started asking questions regarding one of the text books on electronic theory contradicted a couple others, when I asked which was right, and why books A,B, And C all disagreed, but books B and C came closest to being in agreement I was told "There are a LOT of errors in this book, but there's no reason to bring it up" When I asked why in the F he was teaching us out of a book that HE said wasn't accurate I was kicked out of class.

                Always makes me wonder how many brilliant minds are battered into mediocrity by teachers unwilling to spend a half second with them. (don't read that as an ego trip, just wonder how often people who could have been great were dropped by the wayside because a teacher didn't feel like answering their questions)

                Ken.

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                • #9
                  Originally posted by kendall
                  ...Always makes me wonder how many brilliant minds are battered into mediocrity by teachers unwilling to spend a half second with them. (don't read that as an ego trip, just wonder how often people who could have been great were dropped by the wayside because a teacher didn't feel like answering their questions)
                  Ken.
                  It appears to me that the educational system is broken. The curriculum has been fixed by the "powers that be", or the laziest of the teachers, sometimes one in the same, to define some vague middle course - placing all students on a college track - preparing students to be students.

                  In the past there were tracks - trade or college, and perhaps a little extra effort spent on the very bright students.

                  I could have done well in either of the lower or upper programs, instead of being bored and almost failing in the "standard" program.

                  I won't blame all teachers, as they have to work with the structure they are given.

                  Sorry for the hijack.
                  Weston Bye - Author, The Mechatronist column, Digital Machinist magazine
                  ~Practitioner of the Electromechanical Arts~

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                  • #10
                    At the risk of being pedantic, I'm not sure why you've singled out magnetism. I think of magnetism as another form of energy. Heat, light, mechanical, electrical are all forms of energy. You cannot hold any of these forms of energy in your hand, put them into containors, or capture them in any way. You can easily capture the effects of them, IE, a hot bolt, and put it into your hand, but you cannot capture the energy that made it hot. If you could do that, then the idea of insulation would be obsolete. Just put a little heat energy into your containor, and keep it for those occasions where it might come in handy. After time, the effect of heat energy dissipates and your coffee gets cold again, and you need to add additional heat energy to warm it back up. Same idea with all forms of energy. To me, it's simply something that I accept as part of our physical world. We've learned ways to control it, convert it, change it, "see" it, measure it, use it, and the list goes on, but I'd stop short of defining it as anything other than pure energy, which in my little pea-brain, is basically un-definable.
                    There is no shortage of experts, the trick is knowing which one to listen to!

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                    • #11
                      ????

                      ????
                      http://en.wikipedia.org/wiki/Magnetic_Field

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

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                      • #12
                        Always makes me wonder how many brilliant minds are battered into mediocrity by teachers unwilling to spend a half second with them. (don't read that as an ego trip, just wonder how often people who could have been great were dropped by the wayside because a teacher didn't feel like answering their questions)



                        A lot.

                        My niece has always been 'scary smart'. She is 14 now and in high school. They pretty much let here write her own cirriculum in math and science.She taught herself algebra when she was 10. Why? In her words, "the math games I make up in my head to keep myself from being bored in class were getting too easy."

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                        • #13
                          I would not trust the Wikipedia article that tiffie linked to as it contains a statement that demonstrates the person who wrote it isn't actually familiar with magnetism.

                          He writes "The magnetic inductive current represents lines of force. In particular, it represents lines of inverse square law force.


                          This is entirely incorrect. The magnetic lines of force produce a field that obey inverse cube law, not inverse square law. An electric field is dependent on the area of the source and so obeys inverse square law with distance. A magnetic field depends on the volume of the source and so diminishes as the inverse cube of distance.
                          Free software for calculating bolt circles and similar: Click Here

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                          • #14
                            Originally posted by Rustybolt
                            Always makes me wonder how many brilliant minds are battered into mediocrity by teachers unwilling to spend a half second with them. (don't read that as an ego trip, just wonder how often people who could have been great were dropped by the wayside because a teacher didn't feel like answering their questions)



                            A lot.

                            "

                            After you catch a teacher trying to either dodge your question and/or answer it incorrectly so many times it then becomes your responsibility to take control of the situation, Yes it is a shame --- but most part for the closed minded teacher who will not learn themselves. If a student is truly "great" come hell or high water nothing will slow down their momentum, thats not an "ego trip" either -- its just a plain fact.
                            In my high school they had power mechanics 1 and 2 --- by the time I got done with two they created PMech.3 --- it was only me and 4 other guys and yes a GREAT teacher, I was the lead student --- it was a great thing to have a teacher like that BUT --- the fire already started way before that and I was like an information sponge with or without him, still what a great thing to have -- he was really the first guy (besides my bro's or Dad) I can remember who I could bounce idea's off of and that in itself was probably most important in those early years.

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                            • #15
                              Electricity and Magnetism

                              Originally posted by Evan
                              The magnetic lines of force produce a field that obey inverse cube law, not inverse square law. An electric field is dependent on the area of the source and so obeys inverse square law with distance. A magnetic field depends on the volume of the source and so diminishes as the inverse cube of distance.
                              Thanks, Evan. Your explanation is in part new to me especially the use of the two progressions, square and cube. I was going to offer something similar in that magnetism and electricity are two manifestations of the same basic energy. Electricity is where this energy is polar (dipole) which poles hate being apart but always seek to rush together, negentropy; i.e., spark, short or void their polarity (potential/charge). Magnetism is just the opposite in that the two poles push apart, entropy. Whereas opposite poles of a magnet appear to attract each other this may not always be true :>;. If a second magnet is added to the end of a magnet the two poles of both combine and move to the ends - indicating the two poles (of a unit magnet) are trying to get as far away from each other possible. Anyway the magnetic force, in of itself, is expansive or dispersive while electricity is attractive or contractive. I did a sketch of this shifting magnet pole here:



                              PS: NC means Neutral Center.
                              Last edited by dalesvp; 01-08-2009, 02:46 PM.

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