Heat transfer by radiation and absorbion?

Question

A little confused here....
Could anyone explain, the relationship between the ability of one body (non-black) to absorve heat that is emitted by another body (non-black) and the spectrum of the emitted energy.
To make it more clear :
- one body emitts heat at a specific spectrum (at certain wavelengths) depending on the surface temperature. Can this spectrum be shifted or concetrated in a small band at a specific wavelength value?
- the ability of another body to absorb energy, can be characterised by specific wavelength ? E.g. is it correct to say, that a specific body absorbs (the most) at a specific wavelengh?

Thanks in advance.

Answer 1

To answer your first question. Take for example Hydrogen gas in a discharge tube. It's quite easy to verify that the atoms are emitting radiation at (actually it's more correct to say, around) specific wavelengths. Just pass the light through a prism of diffraction grating. Nonetheless, the intensity of the spectral lines emitted from a tube filled with hydrogen gas will be a function of the gas temperature. However, nothing can be done to the make the gas in the tube look like sunlight. The same is true of the opposite, that is an object whose spectrum is broad.

Answer 2

Wien's law does shift the peak frequency with changes in temperature of black and real bodies. However, higher temps result in higher spectral emissions at ALL frequencies so effectively the frequencies spread with higher temps instead of concentrating in small bands. It is a common error to think that all of the energy is being emitted at the one peak.

So for real bodies it depends on the specific emissivity and absorption characteristics, but whatever the specific parameters, the hotter body always transfers energy to the cooler. The greater the difference, the more energy gets transferred.

Answer 3

Hi. Good question. The heat will, of course, go from the higher heat containing body to the lessor. I think you're asking if a red object gets hotter if the frequencies are concentrated in the red part of the spectrum than if they are spread out. I really don't know, but my guess is that the TOTAL energy has more of an influence.