MadSci Network: Physics

Re: Infrared radiation and heat transfer?

Date: Mon Apr 30 11:46:33 2001
Posted By: Juan Cabanela, Faculty, Physics, Astronomy, & Engineering Science, Saint Cloud State University
Area of science: Physics
ID: 987633833.Ph

1. Will a body emit infrared radiation if it's surrounding environment is 
at a higher temperature?

Of course, all dense objects (a.k.a. bloackbodies, or at least good 
approximations to them) at temperatures higher than absolute zero 
will radiate infrared radiation (and other kinds too, depending on the 
temperature).  However, remember, that good blackbodies not only 
emit radiation, they absorb it too.  You are describing a situation here 
where the rate of energy absorption from the hotter environment will 
be higher than the rate of energy emission by the object.

2. Is radiant heat absorption only absorbed by free(unbound) 
electrons within a body?

No, there are all sorts of ways energy can be taken up into an object, 
including in the form of vibrational energy in molecules or in a crystal 
lattice, rotational energy in molecules, and so forth.  Energy can be 
absorbed into a body by many means.

3. Can bound electron photon absorption be converted to heat if the 
photon's energy is less than the ionization energy for that bound 

If a photon has less energy than necessary for the electron in your 
atom/molecule to be ionized, there are two possible outcomes of the 
interaction between that photon and the atom/molecule.  If the energy 
of the photon EXACTLY corresponds to an energy difference between 
electron orbital levels in the atom/molecule, the photon can be 
absorbed and the electron can jump up to a new orbital.  The other 
possibility, the photon energy doesn't correspond to the energy 
difference between orbitals and the photon passes through the 
atom/molecule.  However, that photon's energy can be converted into 
heat by other methods of converting its energy into heat including 
absorption of the photon into vibrational energy in the crystal lattice or 
an individual molecule or absorption by a free electron in the body.  
Note that these are not the only ways to have that photon's energy 
converted into heat, just some possibilties.

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