Material absorbing electromagnetic energy while ignoring another energy from other frequencies?

Question

What are the instances you can think of, where a material may absorb electromagnetic energy of a certain frequency (colour) range while ignoring energy coming at other frequencies?

Example:
Plants absorb electromagnetic energy in the form of visible light for photosynthesis, but may not do the same with radio waves or X-rays, which are also electromagnetic waves.

Answer 1

well, how about a microwave's affect on a potato, compared to visible light, or radio length waves.

with enough energy, you could get some heat-up (absorption) at most any frequency but not the inside out efficient heating that you get with microwaves.

Answer 2

All materials have different absorption/scattering properties. What are you asking? The microwave door is a good example. A metal grate that reflects microwaves, but obviously you can see through.

With your plant example, it's still just 'engineering', as a very large thick pile of leaves will block radio waves or X-rays. Although, if you go to very low frequency, the pile of leaves will need to be extremely large.

Take the ocean, it is permeable to blue light down to hundreds of meters, but even then, it eventually blocks the incoming radiation. And it blocks most other radiation quite well, but VLF radio propagates pretty well. That was the only way to talk to submarines when the were submerged.

So to answer your question, you can construct a filter out of numerous materials. And change the characteristics of the filter base on the construction. Take common glass. Additives in the crystalline matrix absorb various frequencies and scatter others. Hence, colored glass. Everything known to man has some of the same properties, except a pure vacuum.

Answer 3

The refractive index is the ratio (measure) of the speed of light in vacuum to the speed of light in the material.

Theory and experiment has confirmed that the refractive index of any material increases with the increase of frequency in the entire frequency range (with some exceptions).

This shows that the energy is not absorbed by any material.

But there are exceptions as already noted.

There is some region in the immediate vicinity of frequency called resonance absorption.

This region is called anomalous dispersion region.

A substance may have several resonance frequencies which correspond to the differences between its energy levels. Hence there will be a corresponding number of anomalous dispersion regions.

Thus, the index of refraction of a wave, and hence the velocity of propagation, greatly depends upon the value of the wave frequency relative to the natural frequencies OF THE MOLECULAR DIPOLES.

Energy is absorbed in the immediate vicinity of frequencies called resonance absorption frequencies.

Answer 4

The atmosphere is prone to absorbing blue light.

All kinds of different gases have certain frequencies that they are more likely to absorb and re-emit. This is part of the fundamental observations that lead to quantum mechanics.

The electrons can only switch their orbits between certain energy levels. Those energy levels correspond to the energy quanta that they atom can absorb. Different frequencies of light carry different amounts of energy.

This is also noticed in the photoelectric effect experiments of Enstein. He noticed that certain frequencies of light were more likely to be absorbed by the metal and thus eject an electron and cause a current in the metal.

Certain kinds of automotive glass are good at blocking UVB rays while letting everything else through. The same thing is true about Argon filled double pane windows. They let the visible light through and trap the InfraRed thus cutting heating bills.

Lots of things are RF transparent while completely stopping visible light. Examples of this includes most opaque plastics.

OH, ruby lasers, neon lasers, CO2 lasers, are all examples of using the absorption preferences of certain substances to take chaotic energy and turn it into coherent monochromatic energy. I hesitate to use the word light because CO2 lasers do not emit a visible beam.

Answer 5

Almost everything absorbs some frequencies and reflects others. Only a true black body will absorb all frequencies, and such a thing does not exist in nature; in particular, as the frequency decreases and the wavelength increases, the body will not absorb energy whose wavelenght is close to or longer than the size of the object.