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3D Visualization of Electromagnetism

  1. Oct 9, 2011 #1
    I would like some help in visualizing electromagnetism in three dimensions. I have researched extensively and have come up with nothing but sine waves and pond ripples. But just like sine waves representing sound, which are three dimensional compression waves, do not represent how sound actually looks, the perpendicular sine waves of electric and magnetic fields do not represent how electromagnetism actually looks (which I do realize is somewhat paradoxical, trying to visualize the very thing by which we are granted the very capability).

    I know that electric fields are three dimensional, and so are magnetic fields, like spheres. How can they have direction (the vectors on sine waves) if they are "spherical" and thus pulling or repulsing from all around? Is the electric field positive or negative? How can they be perpendicular to one another (a magnetic field has poles, but an electric one?)? When either an electric or magnetic field moves and creates the other, where is it located? For example, a moving magnetic field creates an electric field - where is the electric field? Superimposed on the magnetic one, or offset?

    And how do electromagnetic fields propagate through space? Sorry if this is a lot to answer - my dilemma over visualizing fluctuating electromagnetic waves has led to the subsequent problems of not understanding its propagation and so forth. And after looking over related topics, I have noticed a great deal of equations being given - I wouldn't understand any of that. All I really need is a picture or description of electric and magnetic waves propagating through a vacuum in THREE dimensions, not one or two as is so popular :)

    Thank you so much, any answer would be enormously appreciated!
     
    Last edited: Oct 9, 2011
  2. jcsd
  3. Oct 10, 2011 #2

    Drakkith

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    Staff: Mentor

    Well, first of all a static electric or magnetic field cannot be expressed by a sine wave, as it is non changing. Both the electric and magnetic fields have a "direction" only because we have defined them as having one. IE if I put a positive test charge in an electric field and it goes away from the source then I know the "direction" of the field is pointing away from the source. The field itself has no intrinsic direction, we just put one there to help us out. Also, the field is neither positive nor negative. It is simply there. A positive particle puts out the same field that a negative one does except that particles will react differently to the field depending on whether the particle is positive or negative because the directions are different.

    A magnetic and electric field are perpendicular to each other because that is simply how it works. A changing electric field produces a magnetic field that is at a right angle to it. All the math on this can be found on wikipedia's article on electromagnetism and related links.
     
  4. Oct 11, 2011 #3
    Thanks, that helps a bit - I did mean a moving electromagnetic field.

    Though about the perpendicularity - if electric or magnetic fields are three dimensional, then wouldn't their forces be exerted in three dimensions? Thus how can the forces of magnetic and electric fields be perpendicular if the vectors representing force would be on infinite planes?

    Also, does a moving electromagnetic field mean that a field expands from its source, or does it mean a field is created and moves away?
     
  5. Oct 11, 2011 #4

    Drakkith

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    Staff: Mentor

    The magnetic field itself is 3d just as the electric field is. Take a look at this: http://upload.wikimedia.org/wikipedia/commons/3/3e/Manoderecha.svg
    The B field is caused by a current in the wire and is perpendicular to the current. The innermost ring would be an area where the magnetic field is stronger than the outermost ring. It also extends the entirety of the length of the wire, not just in that one plane. Now, the forces from a magnetic field act on a charged particle differently than you might think it would. (This is why vectors matter) A charged particle drifts SIDEWAYS in a magnetic field, no simply away or towards it. If you have a static homogenous electric field a charged particle will drift in a direction that is parallel to the direction of the field. A static homogenous magnetic field would cause the particle to drift in a circle "around" the lines in the B field. It is only when you have an inhomogeneous magnetic field that a charged particle will experience a force moving it away from the source of the field. See here: http://en.wikipedia.org/wiki/File:Charged-particle-drifts.svg

    It's not actually a "moving" field, it is a "changing" field. Moving the source simply causes the field to change. A bar magnet is a "static" field, meaning that it is not changing. If you moved the magnet then the field would be changing in space around the magnet. Think of the field as something that is always there and it is simply that any CHANGE in the field must propagate outwards at the speed of light. So a static source is surrounded by a field that is static as well until something causes the field to change.
     
    Last edited: Oct 11, 2011
  6. Oct 11, 2011 #5
    Wow, that really cleared things up! So since an electric field would pull or push in the direction of the source, the magnetic field (assuming it is homogeneous) would pull or push in a direction perpendicular to the source (causing a particle to move around the source, as you said)?

    An in regards to electromagnetic field propagation - so an electromagnetic wave will just expand in a sphere at the speed of light, away from its source? How does visible light play into this? And photons? Would the light we perceive be a portion of the wave that hits us?
     
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