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What exactly is electric field?

  1. Feb 24, 2005 #1
    Recently I am reading about electirc and electromagnet. I found electric field and the field line a bit confusing. What forms the field, or the field line? Is it photon?
    Secondly, why must electron orbit around proton, and not proton orbit the electron?
    Thanks in avanced.
  2. jcsd
  3. Feb 24, 2005 #2
    to answer your proton, electron question, the proton in someting like 3000 times heavier than the electron. So why donesn't the sun orbit us? (being sarcastic)

    About your electric field, you would have to get an answer from somebody else. I dont know enough to tell you a proper answer.


  4. Feb 24, 2005 #3
    No way!

    Because the proton is over a thousand time heavier than the electron, so it is practically not moved by the reaction force of the electron. In the atoms apart from Hydrogen, there are more than one proton, and neutrons as well.
  5. Feb 24, 2005 #4
    well an electric field is a field that propagates at the speed of light..... ie an introduction of a charge in a system will be followed by setting up of a field in a region of space at the speed of light.......it is an electric or a magnetic field depending on the frame of reference.
    an... aproton is way heavier than an electron......(centre of mass concept)
  6. Feb 24, 2005 #5
    both the proton and the electron "orbit around" their center of mass, but proton is so much more massive that the center of mass of the two is actually very closed to the proton, so, it is like a electron orbiting around a proton.
  7. Feb 24, 2005 #6


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    For the ones that do not know,the proton's mass is approximately 1838 times more than the electron's...

  8. Feb 24, 2005 #7


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    Every charge exerts a force on another charge, whether they be like or opposite. So the energy created between two electrically charged particles
    is considered an electric field. Think of it as Volts per metre.
    I dont think people should reject your question asking about photons right away, because an electrical field does consist of photons(sometimes virtual). The energy between your two (or many more) particles is transimited through photons i.e energy. This flow of energy is what makes up the field.

    Aswell, photons are the massless particles which make up light, light is simply energy at different frequencies (higher or lower energy).

    About your atomic question. You could think of electrons "orbiting" the nucleus because a proton is :wink: 1838 times heavier than an electron, like the planets orbting the sun. And even back it up saying the centrifugal force is what keeps the electron from circling into the nucleus. This is good in a classical sense. But isn't really true. I dont want to get to involved in quantum mechanics (mostly because I can't nearly explain it myself) but, an electron does not follow a path or an orbit. It is free, and has a chance of ending up where ever energy takes it. It is just alot more likely to be found within its probability cloud, which QM has figured out for us. Also, it has a quantised amount of energy that keeps it "in" the atom. What I mean by this is that just like before, two particles (a proton positively charged, electron negatively) create and electric field. In the atom, its alot more complicated, but I think is safe to say that a Coulombic Force plays a role in the path of an electron in an atom. So along with an electron's momentum, quantised energy, electrical charge you will be able to understand more the atomic world. At least for now...

    Just I case you didn't know, an electron is what makes up electricity or electrical flow.

    P.S I apologise if I've made any false statements. If I did there's no doubt Ill be corrected. :tongue2:
  9. Feb 24, 2005 #8


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    That's not true- an electric field does not propagate- it just sits there!

    A sinusoidally changing electric field will induce a sinusoidally changing magnetic field which induces a sinusoidally changing electric field ... i.e. and electro-magnetic field which propagates at the speed of light.

    A single electron or proton will have a static electric field around it. That is simply the assignment at each point of the electric force that would it would cause on any unit charge at that point.

    I'm not sure what you mean by a "field line". I suspect that is the path that such a "test charge" would follow in that electric field.

    An electric field is a vector field and every vector field corresponds, mathematically to a differential equation. The field line through a given point is a specific solution through the point.
  10. Feb 25, 2005 #9
    Hmm.....If I am not wrong, energy should be brought by some force carrier particle. So, besides photon, are there any other massless particle that made up electric field?
  11. Feb 25, 2005 #10


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    Photons are the force carrying particles. They are bosonic with spin of 1.
  12. Feb 25, 2005 #11


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    "Electric" and "magnetic field" are classical concepts.Their "energy" is carried by the electromagnetic waves...Once you quantize this field,then u can forget E and B ever existed...

  13. Feb 25, 2005 #12
    Now for a slightly different view on what an electric field is:

    A "field" is classical physics is something that exists at every point in space. So, a "field line" then is just the value of the field at every point along a given line in space. A field is often described in terms of "lines" because they're easy to calculate or they bring out some intuitive way of visualizing the essentials of the field's spatial geometry.

    Which brings me to the second point. In relativity theory the gravitational field is the geometry of space-time. In the unified theories Einstein worked on after the completion of GR, he tried to "add" the electric and magnetic fields into his geometry of space-time. So, Einstein tried to explain the electric (& magnetic) field(s) as additional aspects of the geometry of space-time itself.

    There really is a discrepency between this point of view and the one that represents E/M fields in terms of virtual photons. I'm not the one who's going to clear that up.
  14. Feb 25, 2005 #13
    In what way can we quantize the field? :confused:
  15. Feb 26, 2005 #14


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    An electric field can be measured by measuring the force on a small test charge (the smallest practical test charge would be the charge on an electron, or a proton).

    An electric field line is a curve that you trace out that runs in the direction of the force everywhere. So if you start a field line out at a point, the direction of the force at that point tells you what direction the field line goes next. You go a very short distance in that direction, then you measure the force on an electric charge at the new location, and then you repeat the whole process to trace out a curve. This curve is an electric field line.

    Electric field lines have some interesting properties. Their direction gives you the direction of the force (by the above defintion) - their density gives you the magnitude of the force.

    While you can always draw a field line for an arbitrary force, the fact that the density of the field lines gives the magitude of the force is a rather special and interesting property of electric fields that leads ultimately to Gauss's law, one of Maxwell's equations. Maxwell's equations are the famous set of equations which describe electric and magnetic forces and which predicted radio waves.

    This set of defintions (of field, and of field lines) isn't very philsophical, rather, I've deliberately attempted to be pragmatic. The defintions above tell you how to measure the field and the field lines - which is the first step of forming a theory of electromagnetism and of understanding the existing theories (such as the previously mentioned Maxwell's equations).

    Other people have already answered your second question very well.
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