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Fundamentally, what is an electric field?

  1. Nov 24, 2009 #1
    I understand the definition of an electric field as a property of space surrounding a charge, but what exactly is this property? You can think about gravity as objects distorting bend-able space... but is there an analogous explanation for electric fields? Or at least some ideas?
     
  2. jcsd
  3. Nov 25, 2009 #2
    Here's a stab at answering your question.

    In Atomic Theory the polarity of charge q is defined as an electron q = -e and the proton q+ = +e, where in classical physics the q+ is called a test charge.

    The static electric field E predicts the motion of a test charge q+ in the presence of the field. The force F on a charge q is:

    F = qE where q is a quantity of charge inserted at a point in the E field.

    The field itself is created by some spacial distribution of charge, typically much larger than the small charge q in question, otherwise the charge in question changes the shape of the E field!
     
  4. Nov 25, 2009 #3

    tiny-tim

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    Welcome to PF!

    Hi czaroffishies! Welcome to PF! :smile:

    I'll leave someone else to answer the main question, but I'll just point out that an electric field is really just three components of the six-component electromagnetic field. :wink:

    Hi SystemTheory! :smile:

    Yes, but that doesn't answer what the field is (especially since it can exist in a vacuum).
     
  5. Nov 25, 2009 #4
    In a vacuum human beings don't exist to infer that electromagetic fields exist in a vacuum!

    In all such problems involving gravity or electromagnetic fields the working definition implies a region of mass or static charge or moving charge inside some system boundary distributed in space.

    A field is used to describe interactions at a distance. What exactly is the field? A mathematical model one can rely upon to predict action at a distance based on past observations. No one knows for sure what causes action at a distance, and perhaps, no one ever will.

    I look at it this way. If electrons dance in a dipole antenna over here (transmitter) they also dance at a much smaller magnitude in a similar antenna over there (receiver). The model that helps predict such behavior is called electromagnetic field and wave theory.
     
  6. Nov 25, 2009 #5
    I asked my professor about this and he didn't have an answer, so I don't really expect anything definite like we have for gravity. It would be nice if someone happened to know something neither my professor nor I know, but I am aware that that's not likely.

    Mostly I was pushing for philosophical conjecture, I suppose. ;)
     
  7. Nov 25, 2009 #6
    http://en.wikipedia.org/wiki/Action_at_a_distance_(physics [Broken])
     
    Last edited by a moderator: May 4, 2017
  8. Nov 26, 2009 #7

    diazona

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    Asking what an electric field, or any physical concept, really is gets you into difficult territory, and besides, it's not really part of physics. At its core, physics only explains observations; it doesn't deal with the mechanisms behind those explanations (although sometimes we speculate about the mechanisms when it makes the science easier to understand). In other words, physics will tell you how things behave, but it won't tell you anything about their underlying nature that isn't reflected in their behavior. In fact, as far as a physicist is concerned, once you know how something behaves, you know all there is to know about what it is; anything further is just idle speculation. (Which can be fun, don't get me wrong, but it's not really science) And we do have a mathematical model for how the electric field behaves, so as far as physics is concerned, that's what it is - it's a value at every point in space that specifies what the force on a unit test charge at that point would be.

    I think I even confused myself writing (and rewriting) that... this is why I stick to the math ;-)
     
  9. Nov 26, 2009 #8

    sophiecentaur

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    If there were a really simple way of stating what an Electric Field 'really is' then it would be on page one of every textbook. The fact is that it isn't simple enough to dismiss with a single statement. Physics does its best to reduce things to their basic nature but there is a limit. Simple analogies can be a snare and a delusion - leading to further misconceptions for the unwary.
    The best you can hope for is statements like "An Electric Field is a thing that causes a force on a charge". The idea of mass / gravity representing a 'bend in space' is useful but only as a simple picture and an analogy. It doesn't mean that it is 'really' what is happening - the concept of 'really' is very shaky in studying the World. It is what it is and that's all.
     
  10. Nov 26, 2009 #9
    I didn't expect anyone to. I mostly just thought it would be nice if someone knew. Back to my gravity example, my introductory mechanics book didn't post "curvature of spacetime" everywhere when the gravity discussion came up. But really, I just like ideas. The math is great, but the ideas are what really keep me going, and I figured there would be at least a few people out there who have thought about this and had their own crazy theories!

    (Even if I was seeking more than philosophical entertainment, what would be wrong with that? Physical truths can always be expanded on. It kind of seems like that's what characterizes the progress of physics, anyway. :) )
     
  11. Nov 26, 2009 #10
    Hye czarroffihies ... just let me say that I agree with diazona... but that I like your way to ask. I don't know how old you are and you don't have to tell me it. I would only like to insist on that marveillous moment of the life (about 14 - 20) when we have to leave our quest for a deep understanding of what the universe is and exchange it for a more efficient behavior... in some way leaving the magic world for a rationalistic one. We don't know what the worls really is but we try to guess the relationship between the objects contained in the world that we are perceiving. So I don't know what an electric field is. Sorry.
     
  12. Nov 26, 2009 #11

    Pengwuino

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    I'm not sure where all this is discussion is coming from, but it is not a mystery as to what fields are. The electromagnetic force is mitigated by photon exchange.
     
  13. Nov 27, 2009 #12
    What is measurement except just a series of locations of events in time and space. The ideas of charge, fields, or photons are just models to predict (or explain) distance/correlation between events: modification of distance if you will. One might consider GR more elegant because it uses time/space itself to explain those modifications.
     
  14. Nov 27, 2009 #13

    tiny-tim

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    Hi Pengwuino! :smile:

    (you mean "mediated" :wink:)

    No, as a matter of physics, the electromagnetic force is not mediated by photon exchange.

    No photons are exchanged.

    "mediated by photons" is just mathematicians' way of saying that the transition amplitude is an infinite series of integrals which include creation and annihilation operators of every possible momentum of a zero-mass spin-1 particle.

    (all other forces, btw, use non-zero masses for this "vector boson")

    Furthermore, the electromagnetic force is also "mediated by electrons" (and positrons) … the transition amplitude also includes creation and annihilation operators of every possible momentum of a particle with the mass of an electron (and with spin-1/2 and charge ±1 and lepton number 1).

    (we could call them the "vector fermions" of the force, but I don't think anyone actually does)

    In fact, most Feynman diagrams contain twice as many virtual electrons (or positrons) as virtual photons, for the obvious reason that each vertex contains twice as many.

    No electron or positron or photon is harmed, or even actually present, in the process. :wink:

    The mystery is why the electromagnetic force uses the particular mass of an electron (and indeed the particular, zero, mass of a photon) when

    i] the electron mass seems entirely arbitrary

    ii] no particle with that mass (electron or positron or photon) is actually involved!​
     
  15. Nov 30, 2009 #14
    An electric field "alters" space as described in Conceptual Physics book. If a charge to which the field is attributed moves, there is further alteration of space and this is called magnetic field.
    I hope this helps.
    Sridhar
     
  16. Nov 30, 2009 #15
    Electric field lines to not have to terminate on charges. A good example is the azimuthal electric field surrounding a region that has a changing magnetic field (dB/dt); i.e., Faraday Law induction. two applications include the secondary windings on ac transformers, and betatron particle (electron) accelerators. In both cases, the electric field lines terminate on themselves, and represent a modification to space by the changing magnetic field (dB/dt).
    Bob S
     
    Last edited: Nov 30, 2009
  17. Nov 30, 2009 #16
    My understanding is that the electrostatic field lines must terminate on a region of static charge. This is similar to gravity terminatining on a region with mass, although I am not familiar with the theory of gravity waves (time delay in the influence of gravitational force).

    The motion of charge (described somewhere, somehow) creates a magnetic field. This couples an electric field in space. Therefore, there is an electromagnetic EM field "caused" by charge motion described somewhere in the problem characterization.

    The rules for EM fields are not the same as for electrostatic fields in accord with Bob's statement.

    Maxwell's Equations reduce to the static electric field when charge is static, as I recall. They characterize the EM field when charge is in motion based on the particular geometry and properties of materials involved. But it's been a while since I solved an EM problem ...

    Here's the Wiki link:

    http://en.wikipedia.org/wiki/Maxwell's_equations
     
    Last edited: Nov 30, 2009
  18. Nov 30, 2009 #17
    Maybe the electric field lines from Faraday's Law are electromagnetic and not electrostatic, but they don't terminate on electric charges.

    The Sun's gravitational field lines at the Earth don't seem to be diminished by the Moon passing between the Earth and the Sun. Do the Sun's gravitational field lines pass through the Moon without terminating?
    Bob S
     
  19. Nov 30, 2009 #18
    Interference patterns exist in EM fields. The classic example of particle-wave duality is light (or electrons) passing through a double-slit.

    http://en.wikipedia.org/wiki/Double-slit_experiment

    I'm not sure how this applies to gravity or electrostatic field models. I'll think about your question re. the moon interfering with the Sun's gravitation on the earth ...
     
  20. Nov 30, 2009 #19
    The OP asks about the similarities between General Relativity and Electromagnetic waves, so I'm posting this link, which has a number of (apparently informed) papers near the bottom on Gravity and Relativity:

    http://www.metaresearch.org/home.asp [Broken]

    I've always wondered how space instantaneously "knows" how to bend the instant I drop some mass into a region? In other words, Newton's view of gravity is instantaneous and I'm not sure how Relativity impacts this assumption, but admittedly, I've never thought much about it.
     
    Last edited by a moderator: May 4, 2017
  21. Nov 30, 2009 #20
    Well, energy/momentum is something, or represents the effect of something. And whatever that something is everything is made of it.

    My interpretation/speculation (and that is all it is) is that "something" is structures in space-time. Or, in another way, alterations to space-time. We see that plainly in gravity as space-time has a structure causing gravity. By loose induction, all physical phenomena, including EM fields, would be different types of structures of space-time. Now, I think string theorist attempt to actually codify this but I don't know much about it. It would have to be a structure which impacts each type of particle differently, where as GR impacts everything the same.
     
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