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A couple of basic questions about electromagnetic waves

  1. Aug 17, 2003 #1
    Hi, I'm new.

    From what I understand, radio waves are generated these days using alternating currents or mechanically moving charges. The highest frequencies that modern technology reaches is somewhere in the bottom of infrared.

    Theoretically speaking, is it possible to emit visible light using the same techniques? All we need is higher frequencies, right?

    Also, are all possible frequencies "charted"? That is, there's radio, micro, infrared, visible light, ultraviolet, gamma...
    But this can go on to infinity; so do we know what happens to extremely high frequencies of electromagnetic waves?

  2. jcsd
  3. Aug 17, 2003 #2
  4. Aug 18, 2003 #3
    I suspect that as one rises up through the infrared level of frequencies from below, overheating becomes a completely disruptive factor for a classic oscillator. Also, if the light range is entered from below, the behavior becomes more and more hard quantum-like rather than wavelike. Red light is still pretty wavelike, but getting on up into the ultraviolet range gets very quantum-like. By the time one gets to the range of xrays and gamma rays, quantum behavior totally dominates. For several years after gamma rays were distinguished from alpha and beta rays in radioactivity they were thought to be neutral mass particles, until someone managed to diffract them (with great difficulty). Cosmic rays hitting the earth atmosphere are sometimes said to produce ultragamma rays, but these should be very hard quanta and scarcely wavelike at all.
  5. Aug 18, 2003 #4


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    Staff: Mentor

    Hi. Welcome. Uh... We call these things "light bulbs." Or maybe I'm missing your question...

    EM radiation is created simply by exciting electrons. And there are lots of ways to do it, most of which can be achieved with electricity (since electricity moves around electrons, obviously). Incadescent lights work on the principle of hot objects give off heat. The electricity excites the electrons in the filament by heating up the filament. Flourescent lights work by the electricity exciting gas in the tube which gives off uv light, which is then converted to visible.
  6. Aug 18, 2003 #5


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    Staff Emeritus
    Science Advisor
    Gold Member

    ElectroMagnetic radiation of ALL energies has quantum and wavelike characteristics.
  7. Aug 18, 2003 #6
    , but manifests these through a widely variable range, from very-much so down to hardly-at-all so.
  8. Aug 18, 2003 #7
    Yeah, you don't hear people talking about 'photons of radio signals' because at (comparatively) low levels of energy like those used by radio, the wave-like properties of the spectrum are the dominant properties.
  9. Aug 18, 2003 #8
    Electrons can surf in long radio waves, but NOT in short gamma waves. There it is pretty much BAM or miss.

    I am not at all in disagreement with Integral's statement. I should remember xray diffraction and the work of Max von Laue and the Braggs; so should you. ----->

    von Laue's crystals

    Bragg's Law
    William Henry Bragg & William Lawrence Bragg

    The experiment that showed gamma rays to be EM waves was by Rutherford and Andrade, and it was written up in 1914. I can't find much stuff about it online.
  10. Aug 18, 2003 #9
    I am not in disagreement with either of you, I was just supporting your argument that certain wavelengths of electromagnetic radiation have tendencies to manifest themselves in different ways.
  11. Aug 19, 2003 #10
    I said: "so should you".

    I should have used 2nd person plural:

    "so should y'all".

    Sorry! :)
  12. Aug 19, 2003 #11
    So that wasn't really directed at me then? Just sorta... everyone?
  13. Aug 19, 2003 #12
    Yes-- just any reader--
    it balances the first clause.
  14. Aug 20, 2003 #13
    "...These two terms, x-rays and
    gamma rays, are used almost synonymously. Usually electromag-
    netic rays coming from nuclei are
    called gamma rays, while those of high energy from atoms are called x-rays, but at the same frequency
    they are indistinguishable physi-
    cally, no matter what their source. If we go to still higher
    frequenies, say to 10 (to the)24
    cycles per second, we find that we
    can make those waves artificially,
    for example with the synchrotron
    here at Caltech. We can find ele-
    ctromagnetic waves with stupendously high frequencies-with
    even a thousand times more rapid
    oscillation-in the waves found in
    cosmc rays. These waves
    cannot be controlled by us."

    -Richard Feynman
    Six Easy Pieces
    P.33, Basic Physics

    So, Cosmic Rays seem to be the
    highest frequency waves anyone
    has discovered.
  15. Aug 20, 2003 #14
    Feynman was a hell of a guy.
  16. Aug 20, 2003 #15
    I wonder what Feynman meant by "... If we go to ... 10 (to the)24 cycles per second ... we can make those waves artificially, for example with the synchrotron here at Caltech." If he meant they are made by the synchrotron itself and not from nuclear reactions inside it, then this would counter what I said and answer Atlas's last question.
  17. Aug 20, 2003 #16

    Here's a site about the synchrotron. What Feynman is
    talking about is obviously
    the radiation coming from
    the accelerated electrons
    as they pass by the magnets:

    Introduction to the SRS
    Address:http://www.srs.dl.ac.uk/TOP/intro.htm Changed:12:10 AM on Wednesday, August 9, 2000

  18. Aug 20, 2003 #17
    Thanks, Zoob! So the particle accelerating fields themselves are still in the RF (Radio Frequency) range?
  19. Aug 20, 2003 #18
    I don't see why there should be any extremes to the spectrum. I would assume that it would be infinite, or close to, with waves ranging from near zero energy to near infinite energy.
  20. Aug 20, 2003 #19
    I meant "particle accelerating fields of actual synchrotrons".
    CERN How does an accelerator work?

    It's RF cavities that accelerate the particle beams.

    The problem of the upper limit of accelerating frequencies in an operating synchrotron is probably a complex one, involving the bending and focusing fields also. That and matters of timing and synchronization come into play. Then comes my issue of overheating that I suggested earlier.
  21. Aug 21, 2003 #20
    Originally posted by Atlas:

    Theoretically speaking, is it possible to emit visible light using the same techniques? All we need is higher frequencies, right?

    In order to try this we need to
    be able to alternate the current
    at a frequency anywhere in the
    range of visible light, and also
    to put this through a conductor
    that we can prevent from over-

    I know that people who want very
    strong magnetic fields, such as
    in induction heating of metal for
    heat treatment, actually use cop-
    per tubing as the coil, and it is
    kept cool by pumping water through
    it to carry away the heat.

    For our experiment we wouldn't
    need a strong magnetic field, so
    I think the main obstacle would
    be generating the frequency we
    need with conventional electronic

    Here, my knowledge ends. I don't
    know what the limitations are or
    what problems to expect.

    Theoretically, though, all that
    needs to be done is to get current
    to alternate back and forth along
    a length of conductor somewhere in
    the frequency of visible light.

    For the conductor think along the
    lines of an inch long wire no
    thicker than a hair. Hardly any
    current but lots of voltage.

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