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Question about color

  1. Aug 25, 2007 #1
    Basically, isn't it safe to say that a single atom is colorless, and that color can only be perceived once multiple atoms are arranged in a manner that will reflect and absorb certain wavelengths of visible light?
  2. jcsd
  3. Aug 25, 2007 #2


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    You're sort of half-right, but off base. Colour is simply the manner in which our brains interpret the optical input of various EM frequencies. Someone who is colour-blind sees the same things that the rest of us do, but in BW, like an old movie. Birds see the same thing as well, but with additional colours because their visual sensitivity extends into the UV range.
  4. Aug 26, 2007 #3
    uh uh, we've shone monochromatic lasers at isolated atoms and they do have color
  5. Aug 26, 2007 #4


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    again, "color" like "pitch" or "loudness" (regarding audio) are perceptual parameters that have a relationship to physical parameters like frequency and amplitude (as well as to our biological mechanism for perceiving such).

    certainly there is visible light that has some association to electro-magnetic absorbtion and radiation done by atoms. so there are certain natural and sorta resonant frequencies of isolated atoms and those frequencies can be interpreted as "color".
    Last edited: Aug 26, 2007
  6. Aug 26, 2007 #5
    I disagree. Individual atoms I think could have a color, as long as they were being irradiated. The frequencies that are emitted by the atom depend on the electrons being excited and falling from quantized energy levels. The spectra emitted would depend on these differences in energy levels. The energy of a photon is given by E=hf, where f is the frequency and h is Plank's constant. The amount of energy lost when an electron drops to a lower energy level is released via a photon with that energy, which is to say a photon of a particular frequency, i.e. color. The color might also depend on the amount of energy levels that are being excited.
  7. Aug 26, 2007 #6


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    Welcome to PF, Acidbath.
    I might be getting hung up on semantics. There's certainly no dispute that an electron returning to ground state emits at a certain frequency (hence lasers). My original response was based upon the fact that I don't consider it to be a colour until someone sees it. It's sort of like the difference between 'sound' and 'noise'. Since an individual atom is far too small to be seen optically, I think of it as colourless. This is purely a personal opinion, though.
  8. Aug 26, 2007 #7
    Thanks for the welcome, I hope to enjoy a long stay. I think this is more of a philosophical point than a physical one. I think it's comparable to the old saying, "If a tree falls in the woods and no one is around to hear it..." By having a color, I assume the poster means a certain radiation signature in the visible spectrum. Since each atom has a unique spectra (hence the study of spectrometry), I would think this is the same as saying each atom has a color. It would in no doubt be low in intensity, and more atoms would mean more photons, but it still remains that the atom emits photons of particular colors depending on the energy levels, among other things, like magnetic fields.
  9. Aug 26, 2007 #8


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    You're welcome, and I'm sure that you will. From your couple of posts that I've seen, you appear to be exactly the kind of person who makes this site so great.
    And that 'If Helen Keller fell over in the woods, would she make a sound?' is exactly what I was referring to as far as frequency vs. colour is concerned.
    I think that we're on the same page, but expressing it differently.
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