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Seeking the simplest analogy possible please :-)

  1. Jul 22, 2011 #1
    Hi,

    I wonder if anyone could help please as I'm really struggling to understand this ! As a total layman all my life (now retired) to everything bar none in physics, no doubt my question will be mere child's play to everyone so my apologies in advance !

    If I've got the following correctly could someone help provide the simplest non-physics analogy possible as to how to understand that an electric charge will automatically create an electromagnetic field ? I understand that positive and negative poles will repel each other whilst their opposites will attract, but what is it about the electrical charge itself that can "initiate", if that's the right word, the electromagnetic field in the first place ? In other words why can't an electric charge remain an electric charge on its own ?

    Really hope someone can help....

    Thanks in advance :smile:
     
  2. jcsd
  3. Jul 22, 2011 #2

    Pengwuino

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    What do you mean by an electric charge remaining an electric charge? As in, why can't you have an electric charge without a surrounding electric field?

    I don't think such an analogy is even possible to explain it.... Everything I can think of is either related to electromagnetism or gravity
     
  4. Jul 22, 2011 #3
    Thank you !

    Sorry about my very poor explanation and understanding. I'd so far gathered that an electric charge was a separate thing altogether from an e/m field, and that when an electric charge did occur (could this be for example lightning ?) an e/m field would appear (milliseconds ?) around it later ?

    Thanks :smile:
     
  5. Jul 22, 2011 #4
    How about thinking of the electric field as a rule of interaction between two charges. The electric field arises due to the presence of charged particles, yet it can only be measured by its effect on other charged particles. So you can think of it like a rule, which simply states "this charge creates a force on this other charge". The relative positions of the charges affects the strength of interaction, so the rule varies in space.

    The electric field could be thought of as a different (mathematical) name for this rule.

    edit - law is a better word than rule (Coulomb's law http://en.wikipedia.org/wiki/Coulomb's_law)
     
  6. Jul 22, 2011 #5
    Oh dear hopelessly lost don't recognise anything sorry ! :blushing: Anything simplistic will do lol ! ....:confused:
     
  7. Jul 22, 2011 #6
    Is it something like lead filings on a piece of paper with a magnet underneath ? Horsehoe shaped.... ?
     
  8. Jul 22, 2011 #7
    it is not always easy to come up with an analogy for certain phenomena...

    maybe if you move up a notch, a level of abstraction can be introduced that would give you something to understand without really understanding...if you know what I mean...heck, I know I did a lot of this back in college...I understood the 'mechanics' of the physiscs without really understanding the physics, but allowed to manage it.

    actually, to this day, I am not sure if any scientist really understands how magnetism works and is able to somehow influence free space and remotely grab things, etc..

    magnetism? you really chose a tough one...

    maybe if you could narrow down what device you are trying to understand, an understandable explanation can be given without getting into the lowest level...
     
  9. Jul 22, 2011 #8
    The charge doesn't "initiate" the field around it. The field is always around the charge and has forever been around the charge. You can't remove the field from the charge and they shouldn't be thought of as different objects.
     
  10. Jul 22, 2011 #9
    Thank you both for your replies. :smile:

    In fact I'm reading a book, which you might or might not have heard of called "The Field" by Lynne McTaggart (summarised at the bottom of the Amazon webpage, URL below), and whilst very interesting gets very heavy going indeed in places !

    On Page 26 the first and relevant paragraph reads as follows….

    "A field is a matrix or medium which connects two or more points in space, usually via a force, like gravity or electromagnetism. The force is usually represented by ripples in the field, or waves. An electromagnetic field, to use but one example, is simply an electrical field and a magnetic field which intersect, sending out waves of energy at the speed of light. An electric and magnetic field forms around any electric charge (which is, most simply, a surplus or deficit of electrons). Both electrical and magnetic fields have two polarities (negative and positive) and both will cause any other charged object to be attracted or repelled, depending on whether the charges are opposite (one positive, the other negative) or the same (both positive or both negative.) The field is considered that area of space where this charge and its effects can be detected."

    http://www.amazon.co.uk/Field-Quest-Secret-Force-Universe/dp/0007145101
     
  11. Jul 22, 2011 #10

    BruceW

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    In classical physics, the electric and magnetic fields follow 4 simple laws called Maxwell's equations. In these equations, charges and currents can be seen as sources of the electromagnetic field.
    So maybe as analogy, you could say that a charge is like a water fountain, where the water is the electric field.
     
  12. Jul 22, 2011 #11

    Pengwuino

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    That is a visualization of the electric fields. That really doesn't tell you HOW or WHY they show up. The filings are only reacting to the field that already exists.

    We understand exactly how it works. Maxwell's equations show you exactly how they work. It is no more strange than how gravity or the strong force works (that is to say, they all have peculiarities, but for the most part we know how they work).

    This is why I would say there exists no good analogy. At the core of this analogy, one could say why does poking your finger in the water create a ripple/wave and you're practically stuck at the same problem with electromagnetism.

    The problem with learning physics is that you have to come to terms with the fact that you're going to start learning about many phenomena that have no analogy or something to compare it to in real life. That's one of the coolest parts about physics in my opinion. You're learning about things that are based on theories that make no intuitive sense and have little resemblance to the way you thought the world worked before you started studying. And at the end of the day, they do an amazing job at describing the world at the scale we know nothing about in our day to day lives.
     
  13. Jul 23, 2011 #12
    Thank you everyone !! :smile: Yes still struggling even with the fountain one unfortunately.

    With you so far but what do you "need", if that's the right word, to have to understand it or open the door to begin with as I come from the art and literary worlds where visualization unfortunately is more or less everything....:confused:
     
  14. Jul 23, 2011 #13
    Regarding my comment...and yours (Pengwuino)
    What I meant to say is that it is not known how exactly it happens, etc. Sure, we know how to model it, but that is far from knowing how exactly it comes about, how it influences free space and all that good stuff. Maxwell's equations have been around for a good 150 years....are you going to tell me that we have known everything about magnetism since then? I don't think so. How about gravity? Just because somebody came up with the "Law of Gravity" does not mean gravity was understood to its core since then....see the definition of http://en.wikipedia.org/wiki/Physical_law" [Broken]. Anyway, that's all.
     
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  15. Jul 23, 2011 #14

    Pengwuino

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    You need to actually go learn physics. That's probably the only full-proof way of understanding how fields work.

    I don't even think showing you animations of charges and their changing electromagnetic fields would answer your question. Your question almost cant be answered other than to say "if you have a charge, you have a field". You have to basically say, look, I have a positively charged sphere or object or whatever and I put a negatively charged sphere or whatever nearby. They'll start to try to come together despite not being in physical contact. In fact, it doesn't matter where you put the negatively charged object, it's always being pulled towards the positively charged object. So we say that there exists something that we call a field that is created by the positively charged object that exists everywhere outside of the positively charged guy.

    One reason the water fountain analogy isn't perfect is because there exists no medium that this electromagnetic force must be transmitted to. If I have a fountain surrounded by water, you could turn the fountain off and the water would still exist. Not so in electromagnetism. If you get rid of the charge, the field goes away.
     
  16. Jul 23, 2011 #15

    Pengwuino

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    Non-sense. Electric and magnetic fields are two sides of the same coin. You can arbitrarily Lorentz boost between electric and magnetic fields and it's fairly obvious that neither holds any real dominion over the other in terms of understanding. The only curiosity in my mind is that we haven't found magnetic monopoles.
     
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  17. Jul 23, 2011 #16
    "So we say that there exists something that we call a field that is created by the positively charged object that exists everywhere outside of the positively charged guy."

    Do you mind if I try working towards the general framework of the "(Zero Point?) Field" this way as I know no other ! :biggrin:
     

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  18. Jul 23, 2011 #17

    sophiecentaur

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    Why should they exist? There is a topological distinction between a loop and a point and those are, respectively are how you can describe a circulating current /movement of a charge and the charge itself.
     
  19. Jul 23, 2011 #18

    BruceW

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    Maxwell's equations would look more symmetric/general if there were magnetic monopoles.
     
  20. Jul 23, 2011 #19

    sophiecentaur

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    Should we demand symmetry in all things - or is it just aesthetically more attractive?
     
  21. Jul 23, 2011 #20

    Pengwuino

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    No, but it's amazing how many things in physics do have symmetries. You could incorporate it into maxwell's equations very easily and it's existence would have some very interesting consequences that might answer a few questions still held over from classical EM,
     
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