Unaffected by EM waves

[Jarryd]

Although i like to think i understand electromagnetic waves there is still something i don't understand:

Why in the case of light waves do some substances not reflect any light out at all (such as glass), i know its because it doesn't 'absorb' the frequencies and therefor photons aren't released, but what is it exactly which causes it to be unaffected by the electromagnetic wave?

 

In the same sense why doesn't all the radio waves and other waves shooting around us drastically effect our body?

[swansont]

Different materials have different resonances for absorption, depending on their molecular structure. Glass happens to be one that does not absorb strongly in the visible range.

 

Glass does reflect light, however. And transparent medium will reflect light according to the change in index of refraction, the polarization and the angle of incidence (the one instance where there is no reflection, for perpendicular polarization, is called Brewster's angle. So all reflected light is polarized parallel to the surface)

[Tom Mattson]

Why in the case of light waves do some substances not reflect any light out at all (such as glass)' date='

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You mean to tell me that you've never seen your reflection in window glass? :-O

[zebov]

Don't forget that photons are "absorbed" when they have enough energy to kick an electron from a lower energy state to a higher energy state. If there is not enough energy in the light to push electrons from one energy state to the next available one, then the light energy will pass through without being absorbed. Different materials have different energy states which the elctrons can inhabit. In semiconductors, the space between the lower energy level and the upper energy level is called the "bandgap." A material with a very wide bandgap will pass through more light than a smaller bandgap. See http://ece-www.colorado.edu/~bart/book/book/chapter4/ch4_6.htm for info on how this works in semiconductors.