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Homework Help: Electric & Magnetic Field & Polarization

  1. Nov 14, 2008 #1
    1. The problem statement, all variables and given/known data

    I am trying to understand electromagnetic radiation....(the wave propagation of electric & magnetic fields) and resulting polarization. I just cannot visualize it, and once I think I understand, I see some diagram which challenges my thinking. What is the relationship between electric field, electric lines? Is electric field a scalar or vector? I would think it's a scalar but then polarization makes me think it's a field. Polarization: is x-component = the electric field scalar value and y-component = magnetic field scalar value?

    What is the relationship between E_theta, E_phi, and E_r and: electric field & magnetic field/lines/values/etc.?

    2. Relevant equations


    3. The attempt at a solution

    My attempts just confuse me more. A clear description or visualization would be nice. This question is purely for understanding as there are too many things I don't get. That's what happens when all you're taught is the math behind a concept.
  2. jcsd
  3. Nov 15, 2008 #2


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    Homework Helper

    The elecric field is a vector. The field lines in EM waves are the same as that in time-invariant static cases, only that they are time varying.

    Polarisation of plane waves is more complicated. You have linear polarisation, circular polarisation and elliptical polarisation.

    If I'm understanding you correctly you mean to say the E-field of a EM wave is polarised in the a_x unit vector direction, the B-field polarised in the a_y unit vector direction. This is true only if the EM wave is linearly polarised. If not you can expect the E vector to "rotate" about any given wavefront.

    It's hard to explain what this means in words. You can play around with this tool:
    http://www.ece.nus.edu.sg/stfpage/elehht/Teaching/EE2011/Animation/Polarization/polarization_3D_view.html [Broken]
    Last edited by a moderator: May 3, 2017
  4. Nov 15, 2008 #3
    I guess what do the field lines represent? Or what does the electric field vector look like in real life if that makes sense?

    Thanks for the reply. I understand that type of polarization is all about the phase relationship between the x and the y component...but the x & y component of "what" is what is confusing me. For example, take the applet you linked to. The axes given are E_x(t) and E_y(t). I take that to mean E_x(t) = red line = electric field and E_y(t) = blue line = magnetic field. But this must be wrong because I would imagine the axes would be labeled E(t) and H(t) instead. E_x(t) and E_y(t) makes me think that this is only talking about the electric field with no mention of magnetic field at all. Is the applet making any mention of the magnetic field?

    I would expect linear polarization to always have the values of one axes for all t to equal 0 (e.g. E_x(t) = sin wt , E_y(t) = 0 .... and vice versa).

    Hence the bottom line is this: I am confused as to what an electric field vector looks like, how that relates to the electric field lines, and which vectors or axes determine polarization. If I knew that E(t) = sin wt, what would the e-field vector look like, e-lines, and what type of polarization is it? That looks like a scalar value, so how do I get a vector in the first place?

    Sorry, I'm just really confused.
    Last edited by a moderator: May 3, 2017
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