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Color and light

  1. Feb 23, 2014 #1
    I have a question which asks me to estimate the color of a compound in white light. I can easily get the wavelength (hc/dE) as 460nm, which agrees with the book. Looking at a spectrum list that would seem to fall in the blue range, but the book is saying it would be orange because blue is subtracted. What's going on here? I clearly am not understanding something fundamental about light.
     
  2. jcsd
  3. Feb 23, 2014 #2

    DrClaude

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    Staff: Mentor

    The wavelength of what? The wavelength at which the compound absorbs light?
     
  4. Feb 23, 2014 #3
    That's part of my comprehension problem; I'm not sure. All the example I'm working through states is "The wavelength 460nm corresponds to blue light; so the molecule is likely to appear orange in white light (since blue is subtracted)." I understand the first half of that sentence, but not the last half.
     
  5. Feb 23, 2014 #4

    DrClaude

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    My question was a genuine question (not one to make you think). I get the numerator hc, but what is dE?

    My guess is that it corresponds to the energy of a transition in the compound. Therefore, if you shine white light (i.e., the full visible spectrum), what happens to light at 460 nm?
     
  6. Feb 23, 2014 #5
    The dE is a delta-E (la-tex issues using a tablet computer); which is a change in energy.

    I think I follow you now though, if the molecule absorbs blue light it would reflect all other light and appear orange.

    Thanks!
     
  7. Feb 23, 2014 #6
    Absorbs might not be the correct word to use there, the frequency would cancel out between the compound and the white-light.
     
  8. Feb 23, 2014 #7

    DrClaude

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    Absorb is the right word. From of the point of view of the light, "blue is subtracted", as light in that part of the spectrum is absorbed.
     
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