Re: How to make money fast (in science fiction)

On Apr 9, 4:36 pm, Ric Locke <warlo...@[EMAIL PROTECTED]
> wrote:

> Yar. It hits an interesting point, i.e., what's really going on
> regardless of wavelength is photons exciting particles; so why does
> heat-engine theory /work/? More questions only the Anointed can answer.

The first answer that comes to mind is that radiant heat is emitted
over a broad range of wavelengths, and those wavelengths with photon
energies close to that of the photocell's temperature (times
Boltzmann's constant, to turn it into an energy) cannot be efficiently
utilized for energy.  The reason is that photons with less energy than
the band gap energy of the material cannot excite electrons which can
then be turned into a charge separation to create electric work, but
when the temperature gets close to the bandgap energy (or above it),
you get a lot of thermally activated charge carriers that keep the
device from working as a photocell.

On reflection, though, this can't be the whole answer, since you can
imagine taking a hot object and coating it in something with very low
emissivity at long wavelengths but high emissivity at shorter
wavelengths.  Now it will not be emitting photons with energies near
that of the temperature of the photocell, so the former argument does
not apply.  The emitted light still carries entropy, however, and that
absorbed entropy must still be discarded as heat, so you cannot use
all of the absorbed energy to create work.

Another possible explanation is that photons with an energy above the
band gap energy can only deliver the band gap energy as useful work,
all the rest is lost as heat.  Again, this cannot be the whole answer
because you can design a material with multiple layers of
semiconductors, with a continual gradation of band gap energies from
the highest at the top layers to the lowest at the bottom.
Semiconductors tend to be mostly transparent to photons with energies
below their band gap energy (I'm ignoring complications like indirect
band gap materials, here), so photons will go through the layers until
they hit the layer where they have just slightly more energy than the
band gap, where they are absorbed and deliver almost all their energy
as electrical work.

I'll need to think more on this subject ...

>
> <fx:places a drop of Jim Beam Black on forehead, just over "third eye">
>
> Nope, that didn't work.

Heh.  I'm sure you can find a good use for the rest of the Jim Beam,
though ...

Luke