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Electro magnetic wave and light

  1. Apr 8, 2005 #1

    What is the difference between light (photons) and electromagnetic waves (eg radio waves)?
    According to some tables (like this ) the only difference is its wave length. But to me this doesen't make sense! i learned, that a photon just acts like a wave. furthermore a photon has got a mass (rest mass=0) , but i never heard this about em-waves.
    Uh, and it would be possible to slow down the speed of light if it were a 'normal' em-wave, wouldn't it? Urks...

    if it would be possible to compress the wavelength of a radio wave, till it has the same elongation as a light wave (about 500nm), what would happen?
    What would i see?

    Hmm, i hope you understand my question and hopefully it's not too silly. :)

    thanks for your help!
    Last edited: Apr 8, 2005
  2. jcsd
  3. Apr 8, 2005 #2
    Light behaves as a wave but also as a stream of incident particles. these particles are the photons. basically, a photon is a particle that corresponds to an energy-quantum : a little piece of EM-energy.

    So both visions (photons <-->waves) are dual. Just compare it as using two different languages to say the same....

    Indeed a photon has restmass = 0 and it always has velocity = c.

    The EM-energy is quantized, which means it can only have certain values and such an energy-unit really is a photon.



    (though, i don't know whether you will understand everything in this article, it gives a good image of what is goin on)
    Last edited: Apr 8, 2005
  4. Apr 8, 2005 #3


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    Light is just one kind of electromagnetic wave. Wavelength and frequency vary inversely with one another to describe different types of EM waves. If you're using the word 'photon' to describe light, you can equally use it to describe X-rays, microwaves and radio waves, all of which belong to the electromagnetic spectrum.

    A radio wave is exactly the same as a light wave, except that its frequency is a lot lower and its wavelength is a lot higher.
  5. Apr 8, 2005 #4
    Thanks brewnog.

    This means, the maxwell equations are valid for light-waves too; ok, that's not very surprising for me. But that an x-ray could be described as a photon stream is very interesting.
    Last edited: Apr 8, 2005
  6. Apr 8, 2005 #5


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    Just a terminological note here. In common usage, "light" usually means visible light, but in the astro literature I've seen, "light" can refer to electromagnetic radiation of any wavelength, including radio waves and x-rays. I don't know what the standards are in other fields. As for the difference between photons and classical waves, I think that was answered well by marlon.
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