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What do electromagnetic waves look like in 3 dimensions?

  1. Jul 23, 2007 #1
    What do electromagnetic waves look like in 3 dimensions?

    In my textbooks etc. they are always represented as the standard sine wave. But what about actual 3 dimensions?

    Are there waves with smaller wavelengths than gamma waves?
     
  2. jcsd
  3. Jul 23, 2007 #2

    mgb_phys

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  4. Jul 23, 2007 #3

    xez

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    b) They call high energy photons gamma rays, though
    that's just a name. You could have arbitrarily high
    energy photons with arbitrarily high frequency and
    arbitrarily short wavelength. I don't recall that there's
    a limit as to how short the wavelength can be and have
    it still be something you could 'call' a gamma ray.
    The main thing is that past certain limits it becomes
    VERY difficult for gamma rays to be produced with any
    higher energies. Nuclear reactions often produce gamma
    rays. Matter and antimatter annihilations produce even
    higher energy gamma rays.
    And some very extreme cases involving things like
    black holes, supernovae, etc. can produce quite intense
    high energy gamma ray bursts:
    http://en.wikipedia.org/wiki/Gamma_ray_burst

    The practical 'limit' is essentially how high energy of
    a matter-anti-matter collision you could have in the
    universe, and above certain limits they just don't happen
    often in ways we can (or would want to directly!) observe.


    a) That gets 'complicated' well not really complicated, but
    it's a matter of interpretation. You can view an
    electromagnetic wave as a classical (classical physics E/M
    theory) wave. The wave has an electric field strength E,
    a magnetic field strength H, and the E vector is at right
    angles to the H vector in free space. Being a transverse
    wave E and H both are at right angles to the direction
    of propagation in free space.
    The E and H are just intensity vectors of field components,
    at any given point in space and time, though, and
    aren't really saying anything about the 'shape' of the
    overall field or photon unless you add additional
    equations or information to say how E and H vary in
    space to get the 'shape' of the field. How E and H vary
    in TIME and SPACE, though, in areas free of SOURCES
    of new EM waves is dictated by Maxwell's equations so
    they'll tell you how an EM wave, once created, will
    move in time and space.

    However you can also look at EM fields as composed of
    quantum particles called photons, and then you can use
    QED theory to look at the 'shape' of the photons in
    terms of their probability of having a given E or H
    field intensity and detection probability at any given
    point in space and time. There's no fixed 'shape' to
    a photon since that depends on its emission process and
    the environment it's traveling in. You could 'localize' a
    photon inside a 'box' and of course see wave functions
    and resonance type effects versus the size of the box and
    wavelength of the photon.

    Something like a low frequency manmade radio transmitter
    can produce something like a continuous coherent
    'plane wave' or almost 'spherical wave' of waves that
    have fields that look like your classical smooth amplitude
    perfectly coherent sine waves flowing outward forever.

    Something like an atom that emits a photon from
    spontaneous emission though will pretty much emit
    a photon with some relatively discrete direction and
    as a wave-train that is sort of like a damped sine wave,
    initially strong then decaying to zero after a few dozen
    sine cycles....


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  5. Jul 23, 2007 #4

    jtbell

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    Staff: Mentor

  6. Jul 23, 2007 #5
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