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Question re: emf waves distance & speed

  1. Nov 22, 2014 #1
    I know this may seem a silly question, but i can't find the answer in searches, if 2 emf waves travel at the speed of light in a vacuum and one is a gamma ray and the other a radio wave which one would travel from point a to point b faster? if a radio wave is the size of a building and a gamma ray too small to comprehend wouldn't the gamma ray energy packet move in a direction faster than the radio wave energy packet? It would seem if both went from a and reach b at the same time then radio waves would be moving faster? Thanks for clarity on this.
     
  2. jcsd
  3. Nov 22, 2014 #2

    russ_watters

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    Welcome to PF!

    The speed of light (em radiation) is constant. It does not vary with frequency.
     
  4. Nov 22, 2014 #3
    So then the gamma wave will reach point b before the radio wave.
     
  5. Nov 22, 2014 #4

    russ_watters

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    What? No. How can the gamma wave reach point b faster if they are moving at the same speed?
     
  6. Nov 22, 2014 #5

    Drakkith

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    No, both travel at the same speed and will reach point b at the same time.

    It's important to understand that "wavelength" is not the same thing as "size". If we have two EM waves expanding out from a single point, the wavefront of each one forms a spherical shape around the point. The gamma ray wave has a much shorter wavelength, which means that the electromagnetic forces alternate in direction much faster and over a shorter distance than the radio wave, but both wavefronts are expanding outwards at "c", the speed of light.
     
  7. Nov 22, 2014 #6
    So if 2 air planes are traveling at the same speed and one is flying straight while the other is doing large zig zags they will both arrive at the same time?
     
  8. Nov 22, 2014 #7

    nsaspook

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    Caution bad analogy ahead.
    Think of two prop planes flying at the same maximum possible speed of a propeller plane. One has large propellers spinning at a slow speed/frequency to get to that flying speed the other has smaller propellers spinning at a higher speed/frequency to get that flying speed. They both arrive at the same time but the frequency of the propellers were different.
     
  9. Nov 22, 2014 #8

    sophiecentaur

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    Your picture of the "large zig zags" is not appropriate. Nothing "zig zags" in an EM wave. The fields are transverse and change in amplitude as the wave travels along but that doesn't involve any movement from side to side.
    As an aside, if the wave travels through a medium - like an ionised gas, the electrons will be stimulated to move from side to side and then the speed of the wave is affected and will always be slower than c. But it isn't the waves that are moving from side to side - it's just parts of the medium that move.
     
  10. Nov 22, 2014 #9
    Then its the description of radiowaves being the size of buildings that is throwing me off. You know on those nifty childrens emf charts to show where each area of the spectrum is like visible light etc etc. Each wave is a different size bit the wave is not the course a photon takes the wave is the photon but that leads to the idea of photons stretched out infinitely and deteriorates the idea of beaming out single photons one by one. The nature of photons i suppose is easier to understand as pure mathematics because it works for our applied purposes but to concieve it in our limited perception of reality is a little more difficult.
     
  11. Nov 22, 2014 #10
    Oh and thank you everyone for the input. And please forgive my ignorance
     
  12. Nov 22, 2014 #11

    sophiecentaur

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    Nothing to forgive - and you have less of it now. :)
     
  13. Nov 22, 2014 #12
    I was reading this thread https://www.physicsforums.com/threads/photons-as-waves.250920/
    which makes more sense of the subject that what we call a photon is an "oscillation?" Or maybe transition is a better term between electric and magnetic states which is alot clearer of an answer as to why it has wave qualities but not wave motion.
     
  14. Nov 25, 2014 #13
    i thought i had it for a moment thinking a photon wave was the change between magnetic and electric states but the magnetic field increases with the electric field so thats not right. Your saying amplitude is what gives us the wave pattern we use to measure (it doesnt move in a wave motion as u pointed out) so what does amplitude mean when it comes to photon? The number of them in a given volume?
     
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