On Tuesday 17 July 2007 17:04, Jack Teller wrote:
> Kathryn, actually if these 'somethings' are NOT energy emitters, we
> are talking about light reflection. Then there is the whole bit of
> energy *present in the different frequencies of the source) that is
> absorbed by a surface and re-emitted at a certain (few) wavelength(s)
> [that gives its characteristic color to our eyes], and the surface
> growing warmer as a result of all the other energy absorbed, until it
> reached some equilibrium... (01)
Reflection is rarely of just a "few" wavelengths (exceptions include
interferometric reflection such as that causing the color of butterfly
wings or of oil slicks). Rather, it is subject to an absorptivity or
reflectivity vs. wavelength function that is characteristic of the
material or materials comprising the reflecting matter. Fundamentally,
this is a statistical property of the material w.r.t. to a wavelength.
I.e., how likely it is that a given incident photon will be absorbed or
reflected based on its energy or characteristic wavelength. (02)
EM radiation passing through a gas will show absorption spectra
characteristic of the atoms or molecules comprising the gas. (03)
Likewise, non-black-body radiation (e.g., that caused by electrons
transitioning between excited orbitals or from an excited orbital to a
ground orbital) has specific emission wavelengths. This can happen in
gases or in solid state electronic materials, e.g., and is the physical
foundation for lasers. (04)
But otherwise, emission, absorption and reflection spectra are
continuous functions of wavelength. (05)
Nothing's simple, is it? (06)
> Jack (07)
Randall Schulz (08)
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