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EM waves

  1. May 28, 2003 #1


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    I have some general questions about EM waves since i am somewhat lost from reading and may have misuderstood what I read.

    1) does all EM waves travel through a vacuum? if so are they the same speeds/proportional/inporportional to their frequency.

    2) I now that EM waves are transverse, correct? but can they travel through pretty much anything?

    3) Lets say in a vacuum, the velocity of all EM waves are they nearly 3.00 x 10^8 m/s or what?

    Now for my homework question? An EM wave traveling to the east. AT one instant at a given point its E vector points straight up. what is the direction of its vector?

    my answer is south unless my right hand rule i am using is actually my left hand facing in some wierd direction. can you help me please or am i correct?

    Dx :wink:
  2. jcsd
  3. May 28, 2003 #2
    Really? How come then that a mathematician is the only one who finds the cat (=is always right)?
  4. May 28, 2003 #3


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    Re: Re: EM waves

    fair enough but how come you didn't answer my question? Please dont tell me your link is the answer to my question alexander. I wanted some better assistance but your has been appreciated, sir. Thank You!
  5. May 28, 2003 #4

    Tom Mattson

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    Come on, Dx, this is an easy one. When you listen to the radio in your car, the EM waves traveled through the air (not vacuum). When someone gets an X-Ray, the EM waves travel through their body (not vacuum).

    et cetera...

    Look up "index of refraction" in the chapter on EM waves. The explicit relationship should be there.


    See my answer to your first question.


    Yes, you got it right.
  6. May 28, 2003 #5


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    Well, technically they travel in the spaces between atoms in air, which are empty and hence vacuums. They all have the same speed, c in that vacuum. But when they travel through air, they are delayed by hitting stuff and being reemitted, so their overall speed is reduced.

    BUT by some variants of DSR, which is a new theory going around, photon energy does affect their speed. But this is only apparent in extreme circumstances.

    Yes, they are transverse. But when they travel through dense matter, they tend to get dissipated/lose their energy when they bump into the particles. Usually, high energy photons - eg. gamma rays get dissipated less, and penetrate further. It is possible to shield from low energy em radiation. Close your eyes, and there is your example.

    According to current theories, yes.
  7. May 28, 2003 #6


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    FZ+ and Tom, take a bow!

    Thanks for the clarification. Its much appreciated and clearer now.

    Dx :wink:
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