An object that is a good radiator of electromagnetic waves is also a good...?

Question

-insulator of heat
-reflector of heat
-absorber of electromagnetic waves

Or

-refractor of electromagnetic energy.




Thank you and please explain why you chose the answer you did.

Answer 1

Absorbance and emission are quantum mechanically equally allowed so something that absorbs will be equally as good at emitting.

Answer 2

Is this some multiple choice question? If so, its very strange. The thermodynamic properties of a EM structure is a pretty arbitrary question. Aluminum is used extensively in constructing EM radiators, and is a very good conductor of heat.

Two things about the thermodynamic part of your question. A good heat insulator means very poor conduction of heat. A good heat 'reflector' is actually something that reflects infrared radiation in common parlance. Not a thermodynamic property per se.

What constitutes an object in this question? If you mean any molecule, then you need to look at this in term of quantum electrodynamics. Then the transfer of energy from one spectral band to the other can be quantified. With that you can discuss insulator, reflector, and absorber in terms that are on the same playing field.

If you mean general material properties or engineering structures, then we need more information. What are the objects that you speak of? Where in the EM spectrum are you interested? If it is radio waves, then there is a multitude of literature on antennas and materials used in constructing them. If you move to smaller wavelengths, there is a multitude of applicable examples.

Take microwaves. Or even a microwave oven. Glass is a good insulator of heat, but the microwaves cruise right by, hence the metal grate on the window. The metal grate conduct heat very well, but reflects microwave radiation. So you don't get burned or cooked when you look at you food on account of the combination of the two materials.

My point is that your question would need to be much more specific in order to answer to your liking. And we haven't even addressed refraction. Refraction assumes that EM propagation occurs, so obviously any material interface that you want to discuss in this light (sic.) does not reflect or absorb much (as opposed to the previous answer, which was misleading).

Hope this is of some help.

Answer 3

Thanx to Deflagrated's simple and correct answer. A quantum interaction has a time reversibility sense in that the absorption of a particular photon and subsequent electron jump is just the emission step run backwards, and is similarly favorable.

Karman sounds brilliant, but maybe has a little too much free time on her hands.

Edit: Pulled out my Process Heat Transfer book (Kern). At thermal equilibrium, the ratio of the emissive power to the absorptivity for all bodies is the same (Kirchhoff's law). So the two go hand in hand.

Answer 4

A radiator in this case is an emitter.

The heat answers are out 'cause dishes don't generate any, just the transmitters.

Emitters don't absorb electromagnetic waves.

Refractors, refect electromagnetic waves.

Karman: I believe its a multiple choice.