Why do some em wavelengths get absorbed by electrons while others are not?

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Offline Nicholas Lee

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Why do some em waves get absorbed by electrons and some em waves do not, like visible light gets absorbed, but radio waves get transmission?
What is so unique about visible light photons, for electrons to absorb them, and other em waves.
But radio waves traverse solid matter.
What's the difference in photons of differences of EM waves to electrons.
Or has it to do with the wavelength, and frequency.
Also do some radio wave photons get absorbed, as they pass though a solid block of matter.
But the block of solid matter just consisted of only pure carbon atoms, no different atoms of any kind.
I am very grateful for your help, anything helps even a few words
« Last Edit: 01/05/2016 04:44:00 by chris »


Offline Arthur Geddes

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The question of transmission (refraction), absorption or, reflection has to do with both the frequency of the EM & where the electrons are in the incident medium.

A conductor like silver has electrons loose & distant from the nucleus; easily moved by an electric field.  That's why it reflects light: electric fields can't exist in the silver & sum to zero at its surface (approximately.)  The counter electric field produces a direction vector when summed with the magnetic field which results in reflection.  Metals generally have this property; to varying degrees.

A block of carbon has electrons held relatively tightly; if it's doped, it can become a semiconductor but, just a block of carbon will pass radio freq. EM fields.  Air passes visible light &, that's why the eye & chlorophyl are as they are; in between reflecting & passing is seeing & being colourful.  I suppose carbon is black because as the frequency is increased it becomes sufficient to move the electrons up an an orbital before it reaches the visible range; presumably, before the infrared.  The electrons jumping orbitals must somehow transmit their energy to the atoms themselves to heat things up; probably some harmonics of electron movement do & some don't.

I don't think the eye would work if the atmosphere with radiation belts (?) wasn't opaque to higher frequency EM radiation.