Roy Lewallen wrote:
ut clearly different results in heat. . .
This illustrates a classical confusion between heat and temperature,
probably aggravated by our use of "hot" as a description of temperature
rather than heat. Heat is energy. Absorption or transfer of heat results
in a change in temperature. "Hot" (high temperature) objects radiate
more heat than cold objects. The more heat an object, such as a plate,
absorbs, the higher its temperature. Once this basic distinction is
clear, a lot of the mystery disappears.
There are, of course, other mechanisms of heat transfer other than
radiation, namely convection and conduction. But heat transfer has the
same effect on temperature regardless of the mechanism.
When doing experiments with the sun's rays, you sometimes get
non-intuitive results, because there's a lot of energy (heat) at
wavelengths we can't see, particularly at the ultraviolet end. The
reflective or absorptive properties of an object aren't necessarily the
same at infrared or ultraviolet wavelengths as they are at visible
wavelengths. For an example, you can't see the difference in my skin
when coated with sun block or not. But there's sure a difference in
energy (heat) absorption!
Roy Lewallen, W7EL
There are also complications about temperature when referring to solids,
liquids, and gases. The "temperature" of even a weekly ionized plasma
is quite high (e.g. 11000 K per eV), but that more to do with the
velocity of the ions and the mean free path. There's not much mass
there, so the "heat" is small. That is, even though the ionosphere is
"hot" in a temperature sense, it's not very "hot" in a sensible transfer
of heat sense.
BTW, I think the sunburn is not from thermal absorption, but from
photons with enough energy to make the reaction go. The total energy
in the UV of sunlight is MUCH lower than the total energy in the visible
range. The power spectrum of sunlight is pretty close to the spectral
sensitivity of your eyes (which evolved that way to match, I would think).
At least one reference says that sunburn is a direct reaction to DNA
damage from UV photons. Melanin protects because it absorbs the UV and
turns it into heat.
http://www.scientificamerican.com/ar...s-when-you-get