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Who carries EM radiation?

  1. Jun 16, 2011 #1
    If photons "carry" visible light, and light is just a specific frequency of EM radiation... who carries radio waves?

    [PLAIN]http://www.antonine-education.co.uk/physics_gcse/Unit_1/Topic_5/em_spectrum.jpg [Broken]

    And can an EM radiation at specific frequency be changed to a different frequency? I think a demodulator just extracts an existing sub-frequency from a carrier frequency, so although it "gets a low-frequency signal from an high frequency signal", it does not actually "convert" frequencies. Can a device change EM radiation frequency?
     
    Last edited by a moderator: May 5, 2017
  2. jcsd
  3. Jun 16, 2011 #2
    Photons don't "carry" visible light, they are visible light if they are in the right range. A photon doesn't have to be only visible light, it can be at any of the frequencies in the EM spectrum. The energy of a photon determines the frequency of light, E = hf, where f is the frequency, h is planck's constant, and E is the energy of the photon. So, at low enough energy, the photon can be a radio wave. Yes, it can change frequencies if it changes energy, see compton scattering.
     
  4. Jun 16, 2011 #3
    Electromagnetic radiation of all frequencies, including radio waves, consists of photons. Photons in visible-light frequencies aren't special. Human eyes are just adapted to visible frequencies because to take advantage of the fact that the sun shines so brightly at these frequencies. Snakes can see in the infrared and butterflies can see ultraviolet, so to them, these are also visible-light frequencies.

    EM radiation changes frequency when the observer is moving relative to the source. It's called the Doppler Effect or Redshift. EM radiation can also change frequency when it interacts with a material. For instance the phosphor coating on the inside of a standard fluorescent light bulb converts the ultraviolet radiation produced inside the bulb into the visible light we see.
     
  5. Jun 16, 2011 #4
    So radio waves are made up of photons? Or "photon" is the name used for an "EM wave at frequency between XXX and YYY values"?
     
  6. Jun 16, 2011 #5
  7. Jun 16, 2011 #6
    This gets into a discussion of the particle-wave duality. You can think of EM radiation as being a wave represented by oscillating electric and magnetic fields, or you can think of it as being particles, called photons. Check http://en.wikipedia.org/wiki/Particle_wave_duality" [Broken] page.
     
    Last edited by a moderator: May 5, 2017
  8. Jun 16, 2011 #7
    I know it, I was trying to understand if it works only at "visible light" frequencies, or if my satellite dish is collecting photons. :tongue:
     
    Last edited by a moderator: May 5, 2017
  9. Jun 16, 2011 #8
    Your satellite dish is indeed collecting photons.
     
  10. Jun 16, 2011 #9

    sophiecentaur

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    And so is the transformer in your mains power supply. It's just that each photon (@50Hz) has much less energy so there are proportionally more of them.
     
  11. Jun 16, 2011 #10
    Wouldn't they be electrons?
     
  12. Jun 16, 2011 #11

    sophiecentaur

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    Electrons are flowing in the primary and secondary coils but the energy is transferred as photons - there is no 'electrical' connection.
     
  13. Jun 16, 2011 #12
    Oh, I see, you're talking about electromagnetic induction.
     
  14. Jun 16, 2011 #13
    weird.
     
  15. Jun 16, 2011 #14

    sophiecentaur

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    That's how a transformer works, ain't it?
     
  16. Jun 16, 2011 #15
    Yea, I just wasn't paying enough attention to what you had said. My bad.
     
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