Re: heat value in each color in sunlight - science demo doesn't work well

Chris L Peterson wrote:
>
>
> I think you are seeing a couple of effects. First, by definition a
> colored surface will absorb most of the photons striking it, since it
> reflects only a relatively narrow band. Second, the pigments involved in
> producing the colored papers are probably not very reflective at long
> wavelengths, and about half of the photons reaching your boxes are
> infrared. That is probably where most of your anomalous heating is
> coming from- all of the boxes are pretty good absorbers of IR.

someone wrote to me off-list saying the same thing - that all my
boxes were black at IR.

> It is probably impractical to do this experiment, except qualitatively
> with a black and white box. You just don't have enough control over the
> spectral characteristics of the absorbing materials.


> There are IR
> absorbing window tints- you could try using some to prefilter the
> sunlight.

a solution of Cu2+ ions is supposed to do it (from google). Other filters
are expensive. I was hoping for a cheap and simple demonstration
of a simple concept :-)


> A better experimental approach is probably to use a prism to disperse
> the light, and measure the temperature at different wavelengths. I did
> this once, long ago, with three prisms and three medical thermometers.
> Whatever you do, don't forget to allow for the fact that the temperature
> rise isn't simply proportional to the number of photons absorbed, but
> also to their energies, which are higher at shorter wavelengths.

I'd be happy for a "this is greater than that" demo right now.

As to your other posting -- my budget doesn't run to gold foil :-)
However I'll still try the Al foil to see what happens.


Thanks
Joe


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Joseph Mack NA3T EME(B,D), FM05lw North Carolina
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Relevant Pages

  • Re: heat value in each color in sunlight - science demo doesnt work well
    ... For example were the boxes covered with window glass. ... Window glass is a notorious for absorbing in the near IR. ... > temperature and the black box the most with the other ... > number of photons at each color. ...
    (sci.astro.amateur)
  • Re: heat value in each color in sunlight - science demo doesnt work well
    ... >up a panel of shallow boxes, ... >temperature and the black box the most with the other ... >number of photons at each color. ... spectral characteristics of the absorbing materials. ...
    (sci.astro.amateur)
  • Re: heat value in each color in sunlight - science demo doesnt work well
    ... Second, the pigments involved in producing the colored papers are probably not very reflective at long wavelengths, and about half of the photons reaching your boxes are infrared. ... coloured pigments are even remotely pure wavelength selectors. ... You really want coloured filters in front of identical boxes. ... You just don't have enough control over the spectral characteristics of the absorbing materials. ...
    (sci.astro.amateur)
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