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What does electricity & magnetism travel through

  1. May 19, 2010 #1
    I understand that the electromagnetic field and light are tied together, and they all travel through big groups of photons and they all travel at the speed of light. And I get that light travels through empty space.

    But I am wondering what does electricity and magnetism travel through?

    Sound travels through air, light travels through empty space, but what about electricity and magnetism?


    Thanks!!
     
  2. jcsd
  3. May 19, 2010 #2
    Electromagnetic fields don´t require a medium to support a wave. This perplexing property puzzled brilliant minds for many years. They sought that medium and called it "ether". This medium was supposed to have extremely strange mechanical properties. In 1885 Michelson and Morley found ether may not exist. In 1905 Einstein killed its notion when he published the SR.
    The light you see coming from the sun has made a long journey through the vacuum. I still find "strange" this behavior, but if you focus on Maxwell´s third and fourth laws, you´ll find how the electric and magnetic fields interact in such a way to support the wave.
     
  4. May 19, 2010 #3
    I knew that was how it worked with light but I didn't realize it is the same way with electricity and magnetism. So none of them need a medium, they all travel through empty space.

    Which make sense since they are all part of the same field anyways.

    Thx!
     
  5. May 19, 2010 #4
    Light consists of a magnetic field and electric field. The photon is what carries light and magnetic fields. Because photons have zero mass it travels at the speed of light. Sound is not like or should be theorised anything like light. Sound isn’t a particle that travels.
     
  6. May 21, 2010 #5
    Hi,
    sound (wave) travel through any solid.
    Sound should be just waves!
    phonons are just sound wave.
     
  7. May 21, 2010 #6
    Yes, but unlike photons phonon's are not really actual particles. We treat them as such but there is no real phonon particle.
     
  8. May 21, 2010 #7
    Is a photon a real particle either? Just because we can attribute a momentum too it does not mean it is for certain a particle. The same way we can attribute a frequency to the electron but it does not make it for sure a wave.

    A photon could just be thought of as the smallest change in velocity in the electric field (for a given frequency). Where velocity is the change of position of the field perpendicular to the direction of travel, not the velocity c of the electric field.

    You get p = h/wavelength. It doesn't mean it is a particle, it just has relativistic mass because it has the potential to apply a force on an electron.
     
    Last edited: May 21, 2010
  9. May 21, 2010 #8
    I thought someone might bring that up. However at that point you're just being picky.

    You could make the argument is anything a real particle? The answer is of course in the definition.

    What I meant is that, comparatively, looking at the objects we typically label as particles it doesn't seem to far-fetched to see a lot of differences between phonon's and things we typically attribute to being particles.
     
  10. May 21, 2010 #9
    Well I don't know. Is a phonon not just the smallest change in the velocity of air for a given frequency?
     
  11. May 21, 2010 #10
    In a diode the hole is just as real as the electron. It's not a fundamental quantum particle, it's a "synthetic" one. But it's very real.

    As to the OP, there's no atomic medium that supports light the way atoms support sound waves. But it's oversimplifying to say there's no medium supporting electromagnetic waves.

    Space itself is the medium. The trajectory of light follows the curves of spacetime, the medium through which light travels.
     
  12. May 22, 2010 #11
    If you want to learn more i suggest you google the following

    mitopencourseware

    They have about 1900 lectures
     
  13. May 22, 2010 #12
    The OP, I believe, addressed the subject from a classical point of view.
    Then, the thread strayed away with the inclusion of some elements from QM. Many of those posts are confusing and do not clarify the original question because they trudge into complex questions.
    I´d like to clarify to points:
    A phonon isn't the smallest change in velocity of air.
    As far as i Know, neither classical nor QM theories requiere a medium tu support electromagnetic waves. If I say electromagnetic waves travel in space it doesn´t follow space is the supporting medium
     
  14. May 29, 2010 #13
    The theories don't require it but that's because those theories don't adress underlying mechanisms. And no it doesn't follow that space is the supporting medium of electromagetic waves just because you say it. You'd need to say something much more interesting like perhaps this; the equations of general relativity when formulated in 5 dimensions reduce to 4-dimensional spacetime together with Maxwell's equations.
     
  15. Aug 10, 2011 #14
    So...can electricity be made to travel along a sound wave?
     
  16. Aug 11, 2011 #15

    Drakkith

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    Staff: Mentor

    A sound wave is the result of a collective movement of many many particles. Since air is generally NOT a good conductor, the only way to make a current travel through the particles would be to ionize them, which would impart lots of energy into them and disrupt whatever sound wave happened to be propagating.

    Replace the air with a conductive fluid, and sure. If I make waves in my bathtub a current can still travel through the water.
     
  17. Aug 11, 2011 #16
    Hmmm...I thought air was a better conductive fluid than water...?
     
  18. Aug 11, 2011 #17

    Drakkith

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    Staff: Mentor

    Definitively not! Not only is the density of air very low, which hinders current, the molecules in the air don't easily support a current anyways. PURE water is not a good conductor either, but almost all water contains enough impurities to make it a decent conductor.
     
  19. Aug 23, 2011 #18
    Are photons a medium which sound waves may travel through?
     
  20. Aug 23, 2011 #19
    Photons aren't really a medium in that sense. They are better thought of as a type of energy than as a type of matter. Even if they weren't, the fact that photons travel at c means they are incapable of supporting a mechanical wave.

    On the subject of the OP, I almost think of it as the magnetic field being the medium of the electric field and visa versa. It is the existence of one (and the fact that it's time-changing) that supports the other in EM waves.
     
  21. Aug 26, 2011 #20

    Claude Bile

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    Science Advisor

    Light is electricity and magnetism.

    So in essence, you answered your own question.

    Claude.
     
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