Re: Heat vs IR

[David Shrader <davesh19@xxxxxxxxxxxx>]

Wayde Allen wrote:
> 
> On Tue, 26 Nov 1996, Tom Benedict wrote:
> 
> > The definition of "heat" is pretty fuzzy, so if you disagree with my
> > numbers, I'd probably agree with you (go figure).
> 
> No, heat is just another term for energy!  The definition of a calorie
> (measure of heat energy) is:
> 
>    1 calorie = 4.184 Joules (measure of energy)
> 
> Radiation of any kind (IR, visible light, radio) can therefore constitute
> radiative heat tranfer.
> 
> What tends to be confusing is the concept of temperature, since different
> materials require different amounts of energy to change temperature.  This
> is the concept of heat capacity (The amount of energy needed to raise the
> temperature of a body by 1 degree.).
> 
> When discussing radiation, one uses the purely theoretical construct of a
> fictitious body that absorbs all radiation incident on it (Black Body).
> If this body is at thermal equilibrium, meaning it isn't heating up or
> cooling off, then all of the incident radiation is being re-radiated.
> Using Planck's law you can compute the radiation spectrum of the black
> body if you know its equilibrium temperature.  This is how you get the
> term color temperature.  The color temperature of a light source is the
> temperature that a black body radiator would need to be in order to
> radiate the same spectrum of energy.
> 
> So...the radiation spectrum of something at a known temperature can be
> computed.  This will tell you how much IR is being radiated at that
> temperature.  However, the IR is not the temperature, but rather a
> transfer of heat energy.  This transfer depends on the absorbtivity
> (measure of how close to a black body it is)  of the object as well as its
> temperature!
> 
> I think I'd better quit!
> 
> - Wayde Allen
>   (allen@xxxxxxxxxxxxxxxx)Hey!!

Don't quit now!! For the non technical types why don't you summarize why wavelengths 
from approximately 10^5 microns to approximately 10^2 microns is considered infrared? 
My understanding is that electromagnetic wavelengths beyond millimeter microwaves and 
before the visible spectrum were (ca. 1960 AD) considered "infrared" (below red in the 
visible spectrum). Heated objects, i.e. black body, radiate electromagnetic energy in 
this frequency band and the sensation of "heat" depends upon the absorption cross 
section of the absorbing material.

+ Dave +

"Proclaim the gospel always. Use words if necessary"--St. Francis

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Topic No. 2