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Posting-Version: version B 2.10.2 9/18/84; site rochester.UUCP
Path: utzoo!watmath!clyde!bonnie!akgua!mcnc!decvax!genrad!wjh12!harvard!seismo!rochester!nemo
From: nemo@rochester.UUCP (Wolfe)
Newsgroups: net.cooks,net.flame
Subject: Re: Truth in Advertising?
Message-ID: <3426@rochester.UUCP>
Date: Wed, 14-Nov-84 16:13:30 EST
Article-I.D.: rocheste.3426
Posted: Wed Nov 14 16:13:30 1984
Date-Received: Sun, 18-Nov-84 03:28:14 EST
References: <2559@dartvax.UUCP>, <642@watdcsu.UUCP> <216@pyuxt.UUCP>
Organization: U. of Rochester, CS Dept.
Lines: 29

> >I still can't believe the ignorance prevailing in journalism today!
> >For someone to draw the conclusion that since black cars get hot in
> >the sun, then black pots must radiate lots of waste heat is
> >incredulous!  This person should have at least consulted a basic
> >physics text.
> 
> >On the other hand, an object of colour x can only radiate light (read:
> >heat) of colour x (i.e. that wavelength).  Therefore, a 100% black pot
> >will radiate *no heat* at all.  It will be warm to the touch, though.
> 
> Is this why my physics book used to talk of "black body radiation"
> with the same reverence that it used for "perfectly elastic spheres."
> I think black is the *best* radiator.
> 
> 		Marcus Hand	(pyuxt!marcus)

I hope that all this is also making it to net.jokes!  The energy given
off by "black body" radiation is proportional to T^4 (where T is the
absolute temperature of the object).  The wavelength of the emitted
energy is inversely proportional to the frequency, which is in turn
proportional to the energy (remember "h nu"?).  That's why a black 
piece of steel will glow red when sufficiently heated, etc.  The point
is that the frequency of the emitted radiation has NOTHING to do with
the color of the object.  The color of an object, among other things,
does have an effect on (and is caused by) the frequencies of light that
it absorbs.  As I recall, the best color for absorbing the frequencies
of normal sunlight was found to be green, not black, by researchers
working on solar collectors.  
Nemo